Highly sensitive and selective detection of Hg2+ ions and antibacterial activity using a Schiff-base derivative

Highly sensitive and selective detection of Hg2+ ions and antibacterial activity using a Schiff-base derivative | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Highly sensitive and selective detection of Hg2+ ions and antibacterial activity using a Schiff-base derivative Afnan M. Alnajeebi, Rana Yahya, Alaa Shafie, Amal Adnan Ashour, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5316414/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 22 Dec, 2024 Read the published version in Journal of Fluorescence → Version 1 posted 11 You are reading this latest preprint version Abstract A simple and highly effective Schiff-base fluorescent chemosensor ( S1 ) was synthesized and characterized by 1 HNMR and fluorescence spectroscopy. The synthesized chemosensor was applied for the selective and sensitive detection of Hg 2+ ions. The chemosensor exhibited a strong 'turn-on' fluorescence response in a CH 3 OH/H 2 O (1:9, v/v) solution due to complex formation ( S1-Hg 2+ ) which block photo induce electron transfer (PET). The chemosensor showed significant sensitivity with very low detection limit of 0.002 ppm, making it suitable for trace-level Hg 2+ detection. Furthermore, the S1-Hg 2+ complex demonstrated excellent antibacterial activity against various Gram-positive and Gram-negative bacterial strains, broadening its utility beyond sensing. This dual-functional system offers significant potential in environmental and biomedical applications. Schiff-base Chemosensor Turn-on PET Complex Biomedical applications Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction Schiff bases, characterized by the presence of an imine group (-C = N-), have gained significant attention in recent years due to their versatility in a wide range of applications, from material science to biomedical research. (Antony et al. 2019 ; Kaushik et al. 2023 ; Shekhar et al. 2021 ) These compounds are easily synthesized through the condensation of primary amines with aldehyde or ketone, and their structures can be readily modified to suit specific needs. (Qin et al. 2013 ) Among the numerous applications of Schiff bases, their use as fluorescence chemosensors for the detection of heavy metal ions, has garnered significant attention due to their sensitivity and selectivity. (Berhanu et al. 2019 ) Mercury is a highly toxic element known for its widespread environmental impact and severe health risks. It exists primarily in three forms: elemental mercury (Hg 0 ), inorganic mercury (Hg 2+ ), and organic mercury, particularly methylmercury (MeHg). Mercury pollution originates from both natural events, such as volcanic eruptions and forest fires, and human activities, including coal mining, fossil fuel combustion, and chemical manufacturing. Among these, industrial processes are significant contributors to the release of mercury into the atmosphere and water bodies. What makes mercury particularly dangerous is its ability to migrate easily through ecosystems, accumulate in living organisms, and target proteins in the human body due to its high affinity for thiol groups in proteins and enzymes. (Streets et al. 2005 ; Wang et al. 2004 ) Mercury can enter the human body through direct contact with the skin, inhalation, or ingestion, rapidly binding to thiol-containing proteins. This interaction disrupts essential physiological functions, leading to various health issues, including damage to the nervous, immune, and renal systems. In aquatic environments, elemental mercury and Hg 2+ can be transformed into methylmercury by microorganisms. Given the complexity of mercury behavior in biological systems and its profound health effects, there is a critical need for the development of effective chemosensor to monitor mercury contamination. (Bhardwaj et al. 2021 ; Carocci et al. 2014 ; Clarkson 1997 ) Schiff base fluorescence chemosensors have emerged as a promising solution for detecting Hg 2+ , providing a cost-effective and rapid method for Hg 2+ detection with excellent selectivity and sensitivity. One of the key advantages of Schiff base sensors is their ability to serve as turn-on fluorescence sensors for Hg 2+ . In a typical turn-on fluorescence chemosensor, the Schiff base itself exhibits little to no fluorescence in its free form. However, upon binding to Hg 2+ , a significant increase in fluorescence intensity is observed. This fluorescence "turn-on" effect is particularly advantageous for detecting Hg²⁺ in complex samples. (Behura et al. 2023 ; Musikavanhu et al. 2024 ; Su et al. 2016 ) Schiff bases containing specific functional groups, such as sulfur, nitrogen, or oxygen donors, exhibit high affinity for Hg 2+ due to the strong coordination between these atoms and the metal ion. This coordination alters the electronic distribution within the Schiff base, leading to the observed fluorescence enhancement. (Behura et al. 2023 ; Feng et al. 2016 ; Musikavanhu et al. 2024 ; Udhayakumari et al. 2014 ) Beyond their role as chemosensors, Schiff bases and their metal complexes have garnered considerable interest for their antibacterial activity. The growing threat of antibiotic resistance has spurred the search for new antimicrobial agents, and Schiff bases, particularly in complexation with metal ions, have emerged as promising candidates in this regard. The antibacterial properties of Schiff base-metal complexes are largely attributed to their ability to disrupt bacterial cell membranes, inhibit enzyme activity, and interfere with vital cellular processes such as DNA replication and protein synthesis. (Abu-Dief and Mohamed 2015 ; Ceramella et al. 2022 ) The coordination of metal ions to Schiff bases enhances the lipophilicity and stability of the resulting complexes, which facilitates their penetration into bacterial cells. Once inside the cell, Schiff base-metal complexes can interact with various biomolecules, leading to the inhibition of bacterial growth or cell death. (Al Zoubi et al. 2017 ; Mohamed et al. 2010 ; Naureen et al. 2021 ; Prashanthi et al. 2008 ; Saddam Hossain et al. 2018 ; Saroya et al. 2023 ) The Schiff bases complexes with Hg(II) have been shown to exhibit potent antibacterial activity, particularly against Gram-positive and Gram-negative bacteria. (Halli and Sumathi 2012 ; Pal et al. 2024 ) In this study, we synthesized a Schiff-base chemosensor S1 and thoroughly characterized it using 1 HNMR and fluorescence spectroscopy. Following its synthesis, we applied S1 for the selective and sensitive detection of Hg 2+ ions, observing a significant "turn-on" fluorescence response due to complex formation between S1 and Hg 2+ . In addition to its sensing capabilities, we also evaluated the antibacterial activity of S1 and S1-Hg 2+ complex against various Gram-positive and Gram-negative bacterial strains. This dual-functional approach showes the potential of S1 not only as an efficient chemosensor for trace-level detection of Hg 2+ but also as an antibacterial agent, expanding its application in both environmental monitoring and biomedical fields. Experimental Materials and methods The precursors used in the preparation of the Schiff-base were obtained from reliable commercial suppliers and used without further purification. These commercially available starting materials were carefully selected to ensure high purity and consistency in the synthesis process. Methanol, acetic acid and metal salts (HgCl 2 , NiCl 2 , MgCl 2 , AgNO 3 , KCl, CuCl 2 , CaCl 2 , CoCl 2 , NaCl, CdCl 2 , CrCl 3 , and ZnCl 2 ) used in this study were sourced from Sigma Aldrich and Alfa Aesar. Double-distilled water was employed in all tests. S1 was structurally characterized utilizing Agilent-400 DD2 NMR spectrometer (Agilent, Palo Alto, CA) to accurately analyze its functional groups and molecular composition. Fluorescence measurements were performed using a Cary Eclipse fluorescence spectrometer (Agilent Technologies, Inc., Santa Clara, California, USA) to evaluate the fluorimetric properties of S1 . Synthesis of S1 The Schiff base S1was prepared by combining 0.60 g (3.48 mmol) of 2-hydroxy-1-naphthaldehyde with 0.49 g (3.48 mmol) of 4-amino-6-hydroxy-2-mercaptopyrimidine in 20 mL of methanol (Scheme 1 ). The reaction mixture was refluxed for 20 hours, with its progress monitored by thin-layer chromatography (TLC) to ensure completion. After the reaction completed, the mixture was cooled to room temperature, leading to the formation of yellow precipitates. These precipitates were collected through filtration and washed several times with methanol to purify the compound. The synthesis process yielded an 90% recovery of the target product, confirming the efficiency of the method. 1 H-NMR (300 MHz, CDCl3, δ, ppm): 2.490 (s, 1H), 7.155 (d, 1H), 7.298 (s, 1 H), 7.468 (t, 1 H) 7.661 (t, 1 H), 7.849 (d, 1 H), 8.032 (d, 1 H), 8.403 (d,1 H), 9.506 (s, 1 H), 10.847 (s, 1 H), 13.191 (s, 1 H). Antibacterial activity The disc diffusion method was utilized to assess the antimicrobial properties of the synthesized compounds. To maintain consistency and accuracy, bacterial suspensions were standardized to a 0.5 McFarland standard. This standardization ensured uniform bacterial inoculation on agar plates, which is crucial for minimizing variability in the results. The compounds were dissolved in 1% dimethyl sulfoxide (DMSO). The low concentration of DMSO was selected to avoid any effects on bacterial growth. For each trial, 10 µL of the prepared solution was applied to 6 mm antimicrobial discs, which were then placed on the inoculated agar plates and incubated at 37°C for 24 hours. The antimicrobial efficacy was determined by measuring the zone of inhibition. To ensure reliable data, each test was conducted in triplicate, allowing for the calculation of the mean zone of inhibition and its standard deviation, thereby enhancing the statistical significance of the findings. Positive control discs, impregnated with known antibiotics (Penicillin-Streptomycin), were included to compare the activity of the synthesized compounds with established antimicrobial agents. Fluorescence Measurement The sensing response of S1 was evaluated against a variety of metal ions, including transition Hg 2+ , Cu 2+ , Co 2+ , K + , Ca 2+ , Cr 3+ , Mg 2+ , Zn 2+ , Ni 2+ , Cd 2+ , Ag + , and Na + . To establish a baseline for the sensing experiments, stock solutions of S1 and these metal ions were prepared at a consistent concentration of 100 ppm. This approach ensured that comparisons could be accurately made regarding the sensitivity and selectivity of S1 toward different metal ions. The experimental procedure involved transferring 0.20 mL of the S1 stock solution into a 10 ml volumetric flask, followed by the addition of 0.2 mL of the respective metal ion solution. The mixture was thoroughly shaken to promote interaction between S1 and the Hg 2+ . After allowing the solutions to equilibrate for 15 minutes at room temperature, fluorescence spectra were recorded. This incubation period was crucial, as it ensured that the systems reached a steady state, allowing for a reliable assessment of the sensing capabilities of the sensor Results and discussion Structural characterization The 1 H-NMR spectrum of the Schiff base S1 was recorded at 300 MHz in CDCl 3 , revealing several characteristic signals that confirm the successful formation of the target compound ( Fig. 1 ). Notably, a singlet at δ 9.506 ppm is observed, which corresponds to the proton of the imine group (CH = N), a key indicator of Schiff base formation. This signal confirms the condensation reaction between 2-hydroxy-1-naphthaldehyde and 4-amino-6-hydroxy-2-mercaptopyrimidine, resulting in the formation of the imine bond, which is a defining feature of Schiff bases. Additionally, the presence of a singlet at δ 13.191 ppm is assigned to the hydroxyl (OH) proton of the naphthol group. The downfield shift of this signal indicates strong intramolecular hydrogen bonding between the hydroxyl group and the imine nitrogen, which is commonly observed in Schiff bases. This hydrogen bonding stabilizes the molecular structure and influences the chemical environment of the hydroxyl proton, resulting in the observed shift. Additionally, the singlet at δ 10.847 ppm is attributed to the OH proton of the pyrimidine ring. The presence of this signal indicates that the hydroxyl group is attached to the pyrimidine moiety Other signals in the spectrum correspond to the aromatic protons of the naphthalene and pyrimidine ring. For example, doublets, triplets, and singlets between δ 7.155 and 8.403 ppm are assigned to these aromatic protons, reflecting the complex, conjugated structure of the Schiff base. Fluorescence response of S1 to metal ions The fluorescence properties of Schiff base S1 was studied toward various metal ions When excited at 350 nm, S1 exhibited a weak emission at 703 nm, which is attributed to the occurrence of PET within the Schiff base molecule. PET is a common mechanism in Schiff bases where the fluorescence emission is quenched due to electron transfer from the excited fluorophore to a nearby electron acceptor within the molecule, leading to low fluorescence output. This PET process is highly sensitive to external influences, such as metal ion binding, which can modulate the fluorescence response. To investigate the sensing capabilities of S1 , a variety of metal ions, including Hg 2+ , Cu 2+ , Co 2+ , K + , Ca 2+ , Cr 3+ , Mg 2+ , Zn 2+ , Ni 2+ , Cd 2+ , Ag + , and Na + , were tested for their effects on the fluorescence emission of the Schiff base. Remarkably, among all the tested metal ions, Hg 2+ ions caused a significant enhancement in fluorescence emission (Fig. 2 ). This marked increase in fluorescence was due to the inhibition of the PET process upon S1-Hg 2+ complex formation ( Scheme. 2 ). The binding of Hg 2+ to the Schiff base effectively blocked the electron transfer pathway, thereby restoring the fluorescence of S1 and leading to a "turn-on" fluorescence response. Upon the gradual addition of Hg 2+ ions from 0.01 ppm to 2 ppm, the fluorescence enhancement of the Schiff base S1 increased progressively (Fig. 3 ). As the concentration of Hg 2+ ions rises, more S1 molecules interact with Hg 2+ , leading to a greater inhibition of PET and thus a stronger fluorescence response. The stepwise enhancement of fluorescence demonstrates the high sensitivity of S1 towards Hg 2+ detection, allowing it to accurately sense even trace amounts of Hg 2+ ions. This concentration-dependent fluorescence "turn-on" response confirms the potential of S1 as a reliable and sensitive probe for monitoring Hg 2+ levels in environmental and biological samples. Limit of detection To assess its sensitivity, fluorescence titration experiments were performed over a concentration range of 0.01 to 2.0 ppm of Hg 2+ (Fig. 4 ). The fluorescence response of S1 to increasing concentrations of Hg 2+ showed a distinct "turn-on" effect, attributed to the inhibition of PET upon complexation with Hg 2+ ion. This interaction led to a significant enhancement in fluorescence intensity, which was measured to construct a calibration plot demonstrating a direct correlation between fluorescence intensity and Hg 2+ concentration. The sensitivity of S1 was further evaluated by calculating the limit of detection (LOD) and limit of quantification (LOQ), important parameters that define the sensor ability to detect and quantify trace amounts of analyte. The LOD, determined to be 0.002 ppm and the LOQ, calculated to be 0.008 ppm, indicate the exceptional sensitivity of the Schiff base sensor. These values were derived using the standard formula LOD = 3σ/S and LOQ = 10σ/S, where σ represents the standard deviation of the blank measurements, and S is the slope of the calibration curve. The low LOD and LOQ demonstrate that S1 can detect Hg 2+ at trace levels, making it a powerful tool for environmental monitoring and analytical applications. Effect of Foreign Metal Ions The accurate detection of specific metal ions in complex environments is a key challenge in analytical chemistry, particularly when other metal ions are present that could interfere with the sensing process. Many metal ions coexist in natural waters, biological systems, and industrial wastes, making it essential for chemosensor to distinguish their target ion amidst various potential interferences. In this context, evaluating the effect of foreign metal ions on the performance of a chemosensor is crucial to ensure its selectivity and reliability in real-world applications. For the selective detection of Hg 2+ , the chemosensor was tested in the presence of a wide range of other metal ions, including Cu 2+ , Co 2+ , K + , Ca 2+ , Cr 3+ , Mg 2+ , Zn 2+ , Ni 2+ , Cd 2+ , Ag + , and Na + . These metal ions are commonly found in various environmental and biological samples and could potentially interfere with the detection of Hg 2+ . However, despite the introduction of these competing ions, the fluorescence response of S1 toward Hg 2+ remained unaffected, indicating a high degree of selectivity. The S1 sensor demonstrated a significant fluorescence enhancement upon interaction with Hg 2+ , whereas the presence of other metal ions resulted in negligible changes in fluorescence intensity (Fig. 5 ). This selectivity toward Hg 2+ suggests that S1 can function effectively in complex mixtures. It can reliably detect Hg 2+ without interference from other metal ions, making it suitable for practical applications in environmental monitoring, water quality analysis, and biological studies. Job plot analysis The study of metal-ligand interactions is fundamental in the design of selective chemosensors for metal ion detection, and understanding the binding stoichiometry between a chemosensor and its target ion is crucial for elucidating the nature of their complexation. Schiff base chemosensors, known for their versatile coordination capabilities, often exhibit selective and strong binding with specific metal ions, leading to distinct optical or fluorescence responses. For the detection of Hg 2+ , determining the precise stoichiometry of the sensor-metal complex helps in understanding the sensor binding mechanism and enhancing its practical applications. The binding stoichiometry between S1 and Hg 2+ was investigated using the Job plot method. This method involves varying the molar ratio of the chemosensor to the metal ion while keeping the total concentration constant and measuring the corresponding changes in fluorescence. In the case of S1 and Hg 2+ , the Job plot exhibited a maximum value at a molar ratio of 0.5, indicating the formation of a 1:1 complex between the chemosensor and Hg 2+ (Fig. 6 ). This 1:1 stoichiometric ratio suggests that a single molecule of S1 binds to one Hg 2+ , forming a stable complex that is responsible for the observed fluorescence "turn-on" effect. pH study The effect of pH on the metal-binding capabilities of chemosensors, particularly Schiff base sensors, is profound. Schiff base sensors rely on functional groups such as hydroxyl and nitrogen atoms, which act as key sites for metal ion coordination. The protonation state of these groups is highly dependent on the pH of the environment, directly influencing their ability to bind metal ions. The ability of these functional groups to effectively coordinate with metal ions like is highly dependent on the pH of the solution, as the protonation or deprotonation of these sites can either facilitate or hinder binding. The fluorescence response of S1 to Hg 2+ ions was therefore studied across a wide pH range (2 to 12) to understand how pH impacts the sensor’s performance and binding efficiency. At lower pH levels (2 to 6), the fluorescence response of the SBS in the presence of Hg²⁺ was minimal. This reduction in fluorescence intensity can be attributed to the protonation of the Schiff base functional groups, particularly the nitrogen atoms, which reduces their availability for coordinating with Hg 2+ ions. Protonated nitrogen atoms cannot effectively bind metal ions, thus hindering the formation of the sensor-metal complex. As a result, little to no fluorescence enhancement is observed at these acidic conditions. However, as the pH increases toward neutral levels (7 to 10), a significant enhancement in fluorescence is observed (Fig. 7 ). This behavior suggests that at neutral pH, the protonation is alleviated, allowing the Schiff base to efficiently coordinate with Hg 2+ . The deprotonated hydroxyl and nitrogen groups are now free to interact with the metal ions, forming a stable complex that results in a strong "turn-on" fluorescence response. This pH-dependent fluorescence enhancement reflects the optimal binding of Hg 2+ to the Schiff base at neutral or slightly alkaline conditions, where the metal-ligand interactions are most favorable. Interestingly, at very basic pH levels (above 10), the fluorescence intensity begins to decrease again. This drop in fluorescence can be explained by several factors. First, the competition between hydroxide ions (OH⁻) and the Schiff base for Hg 2+ ions becomes more pronounced at higher pH values. Hydroxide ions can bind to Hg 2+ , reducing the availability of free metal ions for complex formation with the Schiff base sensor. Additionally, the formation of Hg(OH) 2 precipitates at high pH levels further limits the concentration of free Hg 2+ ions in solution. This competition and potential precipitation reduce the efficiency of the chemosensor, leading to a decrease in fluorescence intensity. (Sidana et al. 2022 ) Effect of Time The effect of time on the fluorescence response of the Schiff base chemosensor S1 to Hg 2+ ions was evaluated to determine the optimal duration for achieving maximum fluorescence intensity. Upon the addition of Hg 2+ ions to the S1 solution, the fluorescence intensity gradually increased with time, reaching a maximum after 15 minutes (Fig. 8 ). This indicates that the interaction between S1 and Hg 2+ ions, leading to the inhibition of PET and the subsequent fluorescence enhancement, occurs relatively quickly. After the 15-minute mark, the fluorescence intensity stabilized, suggesting that equilibrium between S1 and Hg 2+ had been reached, and no further increase in fluorescence was observed. This rapid response time highlights the efficiency of S1 as a chemosensor for detecting Hg 2+ ions, making it suitable for real-time monitoring applications where timely detection is crucial. Furthermore, the quick achievement of maximum fluorescence intensity ensures that the sensor can be utilized effectively in practical situations without the need for prolonged incubation times. Reversibility study The reversibility study of the chemosensor provides significant insights into its potential for practical applications in metal ions detection. Reusability is a key criterion for the long-term use of chemosensor, especially in environmental and industrial settings where continuous monitoring is essential. The reversible interaction between S1 and Hg 2+ ions was evaluated by alternating the addition of Hg 2+ ions and the chelating agent EDTA. Initially, the fluorescence intensity of S1 was recorded, showing weak emission at 703 nm. The addition of Hg 2+ ions led to a marked increase in fluorescence intensity due to the formation of the S1-Hg 2+ complex. This fluorescence enhancement is attributed to the binding of Hg 2+ ions to the functional groups within S1 , which likely stabilizes the chemosensor structure and improves its emission properties. To test the reversibility of this sensing process, EDTA was introduced into the solution containing the S1-Hg 2+ complex. EDTA, a well-known chelating agent with a strong affinity for metal ions, effectively stripped Hg 2+ from the S1 complex. This dissociation was reflected in a notable decrease in fluorescence intensity, indicating the successful removal of Hg 2+ ions from the complex. The ability of EDTA to reverse the metal binding process highlights the dynamic nature of the S1-Hg 2+ interaction and the stability of the chemosensor structure during the binding and dissociation processes. The reversibility of the system was further confirmed when additional Hg 2+ ions were reintroduced into the solution after EDTA treatment. The fluorescence intensity was restored to a level comparable to the initial Hg 2+ addition, indicating that S1 retained its binding capacity even after seven cycles of Hg 2+ complexation and dissociation (Fig. 9 ). This reversible behavior demonstrates that S1 can be used for multiple detection cycles without significant loss of performance, which is crucial for cost-effective and sustainable sensing applications. Sensing mechanism The sensing mechanism of S1 as a chemosensor for Hg 2+ ions can be explained by the PET process, which plays a key role in modulating the fluorescence response upon metal ion binding. Initially, in the absence of Hg 2+ ions, the fluorescence of S1 is weak. This weak emission is due to the PET process, where the lone pair electrons of nitrogen in the Schiff base moiety interact with the excited state of the fluorophore. In this unbound state, the nitrogen atom donates electrons to the excited fluorophore, resulting in non-radiative decay of the excited state. This quenching mechanism prevents the fluorophore from emitting fluorescence efficiently, leading to the observed weak fluorescence. When Hg 2+ ions are introduced, they bind to the sulfur, nitrogen and hydroxyl groups of the Schiff base. This binding effectively suppresses the PET process because the lone pair of electrons on the nitrogen is now involved in coordination with the Hg²⁺ ions, making them unavailable for electron transfer to the fluorophore. The inhibition of PET restores the fluorophore ability to emit fluorescence, leading to a significant increase in fluorescence intensity upon Hg²⁺ binding. This PET-based "turn-on" mechanism is commonly observed in chemosensors, where the metal ion binding prevents electron transfer and thus allows fluorescence emission. The fluorescence enhancement observed in S1 upon Hg²⁺ binding is a direct result of the suppression of the PET process, indicating the formation of a stable S1 -Hg²⁺ complex ( Scheme. 2 ). Job plot analysis further confirms that the binding stoichiometry between S1 and Hg²⁺ is 1:1, meaning that one S1 molecule coordinates with one Hg²⁺. This strong metal-ligand interaction stabilizes the chemosensor structure, reducing vibrational and rotational motions that would otherwise lead to non-radiative decay, thereby enhancing the fluorescence intensity. Practical applications The percent recovery results for Hg 2+ ions in real water samples, including tap, pond, and river water, demonstrate the practicality and reliability of the S1 chemosensor in detecting mercury in various environmental matrices. The recovery range, between 90.0 ± 0.27% and 104.0 ± 0.38%, reflects the chemosensor ability to accurately detect and quantify Hg 2+ ions under different real-world conditions, highlighting its sensitivity and selectivity. The recovery rates close to or slightly above 100% indicate that the S1 chemosensor performs well across different water samples. The slight variations in recovery values ranging from 90–104% are within acceptable limits for environmental and analytical studies. These variations can be attributed to the natural complexity of environmental water samples, where factors such as pH, ionic strength, and the presence of natural organic matter may slightly influence the binding efficiency of S1 with Hg 2+ ions. Table 1 % Recovery of Hg2+ form various water samples Samples Concentration of Hg 2+ (µg mL − 1 ) % Recovery Added Found Tap water 0.5 1.0 1.5 0.45 0.95 1.48 90.0 ± 0.27 95.0 ± 0.11 98.6 ± 0.34 River water 0.5 1.0 1.5 0.46 0.97 1.52 92.0 ± 0.43 97.0 ± 0.25 101.3 ± 0.39 Pond water 0.5 1.0 1.5 0.48 1.02 1.56 96.0 ± 0.18 102.0 ± 0.54 104.0 ± 0.38 Comparison of the Sensitivity of S1 with Reported Chemosensors The Schiff base chemosensor S1 was compared with various reported chemosensors in terms of sensitivity for Hg 2+ detection. As shown in Table 2, S1 demonstrated superior sensitivity, outperforming many previously reported chemosensors. Table 1 Compression the sensing performances of chemosensors S1 with different reported chemosensors Methods Colour change Mechanism LOD (µM) pH Medium References Colorimetric & Fluorimetric Yellow to purple PET 0.02 7 Aqueous medium (Kumar et al. 2022 ) Colorimetric & Fluorimetric Colorless to pink ICT 0.05 7.4 NaH 2 PO 4 -Na 2 HPO 4 buffered solution (containing 15% methanol v/v) (Ma et al. 2014 ) Colorimetric & Fluorimetric Colorless to pink ICT 0.01 7 MeCN-HEPES buffer (Dong et al. 2013 ) Colorimetric & Fluorimetric Deep sky blue to blue ICT 0.096 4.5–7.4 Aqueous (Neupane et al. 2012 ) Colorimetric & Fluorimetric Yellow to green TICT 0.25 6.5 NaH 2 PO 4 -Na 2 HPO 4 buffered solution (containing 15% methanol v/v) (Ma et al. 2014 ) Fluorimetric - CHEQ 0.084 - DMSO: H 2 O (1:1, v/v). (Bhanja et al. 2024 ) Fluorimetric - ICT 0.017 - Ethanol-Water (6:4) (Vengaian et al. 2016 ) Colorimetric & Fluorimetric Colorless to pink PET 0.0134 7–13 DMSO/H 2 O (7:3, v/v, 10 µM) (Zhong et al. 2020 ) Colorimetric & Fluorimetric Green to blue ICT & FRET 0.02 - H 2 O/EtOH(1:1) (Srivastava et al. 2013 ). Colorimetric & Fluorimetric Colorless to pink Ring-opening 0.0107 6–9 HEPES buffer (Choudhury et al. 2020 ). Fluorimetric - PET 0.01 7–10 CH 3 OH/H 2 O (1:9, v/v) Present work The detection limit was notably lower, with a value of 0.002 ppm (0.01 µM), indicating its ability to detect trace levels of Hg 2+ ions with high precision. The enhanced sensitivity of S1 can be attributed to its strong binding affinity for Hg 2+ ions, which effectively inhibits PET and leads to a pronounced "turn-on" fluorescence response. Additionally, S1 ability to operate in an aqueous environment, as well as its fast response time, further emphasizes its practical advantages over other sensors that may require more complex conditions or show slower responses. This improvement in sensitivity makes S1 an ideal candidate for applications requiring ultra-sensitive detection of Hg 2+ ions, particularly in environmental monitoring and biomedical fields. Antibacterial activity The data presented in the Table. 3 provides a comparative analysis of the antibacterial activities of S1 and its complex S1-Hg 2+ , and the commonly used antibiotic combination of Penicillin-Streptomycin, against a range of bacterial strains. The bacterial strains include both Gram-negative and Gram-positive organisms, with varying susceptibilities to antibacterial agents. By analyzing the data, we can observe the performance of the S1 compound and its complex S1-Hg 2+ , as well as their potential for enhancing antibacterial efficacy compared to conventional antibiotics. The inhibition zones recorded for each bacterial strain are expressed in millimeters (mm), with larger zones indicating stronger antibacterial activity. Penicillin-Streptomycin, a broad-spectrum antibiotic, generally serves as the control and benchmark for comparison. The performance of S1 and the S1-Hg 2+ complex is evaluated by comparing their inhibition zones with those produced by Penicillin-Streptomycin. Starting with Pseudomonas fluorescens , the inhibition zone for Penicillin-Streptomycin is 19.06 ± 0.69 mm, while S1 shows a lower inhibition zone of 13.77 ± 0.43 mm, indicating moderate antibacterial activity. However, its complex S1-Hg 2+ , increases the inhibition zone to 16.22 ± 0.78 mm. This suggests that the S1-Hg 2+ complex exhibits improved antibacterial efficacy against Pseudomonas fluorescens compared to S1 . For Escherichia coli ATCC 25922 , a similar trend is observed. The inhibition zone for Penicillin-Streptomycin is 18.12 ± 0.89 mm, while S1 shows a lower inhibition zone of 12.34 ± 0.60 mm. However, the S1-Hg 2+ complex increases the inhibition zone to 15.96 ± 0.48 mm, again demonstrating that the complexation improves the antibacterial efficacy of S1 . Although the S1-Hg 2+ complex performs better than S1 , it remains slightly less effective than Penicillin-Streptomycin. Table 3 Antibacterial activity of S1 and S1-Hg2+ against various bacterial strains Zone of inhibition (nm) Bacterial Strains Penicillin-Streptomycin S1 S1-Hg 2+ Pseudomonas fluorescens 19.06 ± 0.69 13.77 ± 0.43 16.22 ± 0.78 Escherichia coli ATCC 25922 18.12 ± 0.89 12.34 ± 0.60 15.96 ± 0.48 Bacillus cereus EMC 19 19.66 ± 0.61 14.28 ± 1.06 16.88 ± 0.86 Pseudomonas aeruginosa DSM 50071 19.22 ± 0.56 13.98 ± 0.76 15.74 ± 0.38 Bacillus subtilis IM 622 20.12 ± 0.70 14.24 ± 0.57 17.82 ± 0.76 Brevibacillus brevis 19.34 ± 0.66 13.58 ± 0.46 15.72 ± 0.72 Proteus vulgaris FMC II 17.32 ± 0.61 10.51 ± 0.41 13.51 ± 0.55 Salmonella typhimurium NRRLE 4413 18.11 ± 0.29 11.73 ± 0.87 14.48 ± 0.98 Klebsiella pneumoniae EMCS 17.75 ± 0.62 10.44 ± 0.70 15.72 ± 0.69 Salmonella enterica ATCC 13311 17.82 ± 0.22 11.63 ± 0.59 13.43 ± 0.71 Enterobacter aerogenes CCM 2531 19.38 ± 0.61 12.74 ± 0.11 15.75 ± 0.60 Staphylococcus aureus 6538 P 18.86 ± 0.46 13.62 ± 0.49 14.63 ± 0.27 Bacillus megaterium DSM 32 18.99 ± 0.92 12.83 ± 0.77 15.84 ± 0.58 In the case of Bacillus cereus EMC 19 , Penicillin-Streptomycin produces an inhibition zone of 19.66 ± 0.61 mm. S1 shows moderate activity with an inhibition zone of 14.28 ± 1.06 mm, but this increases significantly to 16.88 ± 0.86 mm when S1 is complexed with Hg(II). This represents a notable improvement in antibacterial activity, suggesting that the S1-Hg 2+ complex is more potent against Bacillus cereus than S1 alone. For Pseudomonas aeruginosa DSM 50071 , the inhibition zone for Penicillin-Streptomycin is 19.22 ± 0.56 mm. S1 has an inhibition zone of 13.98 ± 0.76 mm, which increases to 15.74 ± 0.38 mm with the S1-Hg 2+ complex. Similar to previous observations, the S1-Hg 2+ complex enhances the antibacterial activity compared to S1 , though it does not exceed the effectiveness of Penicillin-Streptomycin. For Bacillus subtilis IM 622 , the inhibition zone for Penicillin-Streptomycin is 20.12 ± 0.70 mm. S1 shows relatively strong activity with an inhibition zone of 14.24 ± 0.57 mm, but this increases to 17.82 ± 0.76 mm when complexed with Hg(II). In the case of Brevibacillus brevis , Penicillin-Streptomycin shows an inhibition zone of 19.34 ± 0.66 mm. The inhibition zone for S1 is 13.58 ± 0.46 mm, which increases to 15.72 ± 0.72 mm with the S1-Hg 2+ complex. For Proteus vulgaris FMC II , Penicillin-Streptomycin produces an inhibition zone of 17.32 ± 0.61 mm. S1 exhibits relatively weak activity with an inhibition zone of 10.51 ± 0.41 mm, but this increases to 13.51 ± 0.55 mm when S1 form complex. For Salmonella typhimurium NRRLE 4413 , Penicillin-Streptomycin produces an inhibition zone of 18.11 ± 0.29 mm. S1 shows moderate activity with an inhibition zone of 11.73 ± 0.87 mm, which increases to 14.48 ± 0.98 mm with the S1-Hg 2+ complex. For Klebsiella pneumoniae EMCS , the inhibition zone for Penicillin-Streptomycin is 17.75 ± 0.62 mm. S1 shows weak activity with an inhibition zone of 10.44 ± 0.70 mm, but the S1-Hg 2+ complex improves this to 15.72 ± 0.69 mm. This significant increase in inhibition zone indicates that the S1-Hg 2+ complex is much more effective than S1 alone against Klebsiella pneumoniae . For Salmonella enterica ATCC 13311 , Penicillin-Streptomycin produces an inhibition zone of 17.82 ± 0.22 mm. S1 has an inhibition zone of 11.63 ± 0.59 mm, which increases to 13.43 ± 0.71 mm with the S1-Hg 2+ complex. The improvement in antibacterial activity following complexation is modest but notable. For Enterobacter aerogenes CCM 2531 , Penicillin-Streptomycin produces an inhibition zone of 19.38 ± 0.61 mm. S1 shows moderate activity with an inhibition zone of 12.74 ± 0.11 mm, which increases to 15.75 ± 0.60 mm with the S1-Hg 2+ complex. This represents a significant enhancement in antibacterial activity, suggesting that the S1-Hg 2+ complex could be a promising candidate for further development in targeting Enterobacter aerogenes . For Staphylococcus aureus 6538 P , Penicillin-Streptomycin shows an inhibition zone of 18.86 ± 0.46 mm. S1 exhibits moderate activity with an inhibition zone of 13.62 ± 0.49 mm, but this only increases slightly to 14.63 ± 0.27 mm with the S1-Hg 2+ complex. Finally, for Bacillus megaterium DSM 32 , Penicillin-Streptomycin produces an inhibition zone of 18.99 ± 0.92 mm. S1 shows moderate activity with an inhibition zone of 12.83 ± 0.77 mm, which increases to 15.84 ± 0.58 mm with the S1-Hg 2+ complex. This significant improvement suggests that the S1-Hg 2+ complex is more effective than S1 alone. Conclusion Schiff-base chemosensor S1 synthesized in this study has proven to be a highly selective and sensitive tool for detecting Hg 2+ ions. Its 'turn-on' fluorescence response, attributed to the suppression of PET upon complex formation with Hg 2+ , enabled efficient detection at trace levels with a remarkably low detection limit of 0.002 ppm. The simplicity of its design and the high sensitivity make S1 a valuable candidate for practical applications in monitoring Hg 2+ contamination, especially in environmental settings where detecting trace amounts of toxic metals is crucial for public health and safety. Additionally, the S1-Hg 2+ complex exhibited excellent antibacterial activity against both Gram-positive and Gram-negative bacterial strains, demonstrating its potential as a multifunctional system. This dual capability not only enhances the utility of S1 in Hg 2+ detection but also extends its applications into the biomedical field, where antibacterial agents are in demand. The combination of environmental sensing and antibacterial activity positions S1 as a promising candidate for future developments in environmental monitoring and biomedical technologies, providing a platform for further exploration of Schiff-base chemosensors in multifunctional systems. Declarations Acknowledgement The authors extend their appreciation to Taif University, Saudi Arabia for supporting this work through project number (TU-DSPP-2024-58)”. Funding The research was funded by Taif University, Saudi Arabia, Project Number (TU-DSPP-2024-58) Data Availability : All data generated or analyzed during this study are included in this published article Code Availability: ChemDraw Ethical Approval : This article does not contain any studies with human participants or animals, clinical trial registration, or plant reproducibility performed by any authors. Consent to Publish: The authors have approved the paper and agree with its publication. Consent to participate : No applicable. Authors’ Contributions: Afnan M. Alnajeebi: Conceptualization-Equal, Editing-Equal, Rana Yahya, Editing-Equal, Formal analysis-Equal, Dr Alaa Shafie: Supervision-Equal, Writing Original Draft-Equal, Dr Amal Adnan Ashour: Data Curation-Equal, Visualization-Equal, Dr Mohammed Fareed Felemban: Data Curation-Equal, Editing-Equal, Dr Faris J. Tayeb: Visualization-Equal, Formal analysis-Equal, Conflict of Interest: The authors declare that they have no conflicts of interest. References Abu-Dief, A. M., & Mohamed, I. M. A. (2015). A review on versatile applications of transition metal complexes incorporating Schiff bases. Beni-Suef University Journal of Basic and Applied Sciences , 4 (2), 119–133. https://doi.org/10.1016/J.BJBAS.2015.05.004 Al Zoubi, W., Al-Hamdani, A. A. S., Putu Widiantara, I., Hamoodah, R. G., & Ko, Y. G. (2017). Theoretical studies and antibacterial activity for Schiff base complexes. Journal of Physical Organic Chemistry , 30 (12), e3707. https://doi.org/10.1002/POC.3707 Antony, R., Arun, T., & Manickam, S. T. D. (2019). A review on applications of chitosan-based Schiff bases. International Journal of Biological Macromolecules , 129 , 615–633. https://doi.org/10.1016/J.IJBIOMAC.2019.02.047 Behura, R., Mohanty, P., Sahu, G., Dash, P. P., Behera, S., Dinda, R., et al. (2023). A highly selective Schiff base fluorescent sensor for Zn2+, Cd2+ and Hg2+ based on 2,4-dinitrophenylhydrazine derivative. Inorganic Chemistry Communications , 154 , 110959. https://doi.org/10.1016/J.INOCHE.2023.110959 Berhanu, A. L., Gaurav, Mohiuddin, I., Malik, A. K., Aulakh, J. S., Kumar, V., & Kim, K. H. A review of the applications of Schiff bases as optical chemical sensors. , 116 TrAC - Trends in Analytical Chemistry 74–91 (2019). Elsevier B.V. https://doi.org/10.1016/j.trac.2019.04.025 Bhanja, A., Pandey, P., & Murugavel, R. (2024). Carbazole based Schiff base ligand: An efficient “Turn-on/off” sensor for the detection of Al3+ and F− ions and “Turn-off” sensor for Hg2+ ion. Journal of Photochemistry and Photobiology A: Chemistry , 447 , 115269. https://doi.org/10.1016/J.JPHOTOCHEM.2023.115269 Bhardwaj, V., Nurchi, V. M., & Sahoo, S. K. (2021). Mercury Toxicity and Detection Using Chromo-Fluorogenic Chemosensors. Pharmaceuticals 2021, Vol. 14, Page 123 , 14 (2), 123. https://doi.org/10.3390/PH14020123 Carocci, A., Rovito, N., Sinicropi, M. S., & Genchi, G. (2014). Mercury toxicity and neurodegenerative effects. Reviews of Environmental Contamination and Toxicology , 229 , 1–18. https://doi.org/10.1007/978-3-319-03777-6_1/COVER Ceramella, J., Iacopetta, D., Catalano, A., Cirillo, F., Lappano, R., & Sinicropi, M. S. (2022). A Review on the Antimicrobial Activity of Schiff Bases: Data Collection and Recent Studies. Antibiotics 2022, Vol. 11, Page 191 , 11 (2), 191. https://doi.org/10.3390/ANTIBIOTICS11020191 Choudhury, N., Ruidas, B., Mukhopadhyay, C. Das, & De, P. (2020). Rhodamine-Appended Polymeric Probe: An Efficient Colorimetric and Fluorometric Sensing Platform for Hg2+in Aqueous Medium and Living Cells. ACS Applied Polymer Materials , 2 (11), 5077–5085. https://doi.org/10.1021/ACSAPM.0C00878/SUPPL_FILE/AP0C00878_SI_001.PDF Clarkson, T. W. (1997). The Toxicology of Mercury. Critical Reviews in Clinical Laboratory Sciences , 34 (4), 369–403. https://doi.org/10.3109/10408369708998098 Dong, Z., Tian, X., Chen, Y., Hou, J., Guo, Y., Sun, J., & Ma, J. (2013). A highly selective fluorescent chemosensor for Hg2+ based on rhodamine B and its application as a molecular logic gate. Dyes and Pigments , 97 (2), 324–329. https://doi.org/10.1016/J.DYEPIG.2013.01.002 Feng, L., Shi, W., Ma, J., Chen, Y., Kui, F., Hui, Y., & Xie, Z. (2016, December 1). A novel thiosemicarbazone Schiff base derivative with aggregation-induced emission enhancement characteristics and its application in Hg2+ detection. Sensors and Actuators, B: Chemical . Elsevier B.V. https://doi.org/10.1016/j.snb.2016.06.129 Halli, M. B., & Sumathi, R. B. (2012). Synthesis, spectroscopic, antimicrobial and DNA cleavage studies of new Co(II), Ni(II), Cu(II), Cd(II), Zn(II) and Hg(II) complexes with naphthofuran-2-carbohydrazide Schiff base. Journal of Molecular Structure , 1022 , 130–138. https://doi.org/10.1016/J.MOLSTRUC.2012.05.003 Kaushik, S., Paliwal, S. K., Iyer, M. R., & Patil, V. M. (2023). Promising Schiff bases in antiviral drug design and discovery. Medicinal Chemistry Research 2023 32:6 , 32 (6), 1063–1076. https://doi.org/10.1007/S00044-023-03068-0 Kumar, A., Hur, W., Seong, G. H., Kumar, S., & Chae, P. S. (2022). Chromofluorogenic naphthoquinolinedione-based probes for sensitive detection and removal of Hg2+ in aqueous solutions. Dyes and Pigments , 198 , 110025. https://doi.org/10.1016/J.DYEPIG.2021.110025 Ma, L. J., Liu, J., Deng, L., Zhao, M., Deng, Z., Li, X., et al. (2014). Selective and sensitive fluorescence-shift probes based on two dansyl groups for mercury(II) ion detection. Photochemical & Photobiological Sciences , 13 (11), 1521–1528. https://doi.org/10.1039/C4PP00094C Mohamed, G. G., Zayed, M. A., & Abdallah, S. M. (2010). Metal complexes of a novel Schiff base derived from sulphametrole and varelaldehyde. Synthesis, spectral, thermal characterization and biological activity. Journal of Molecular Structure , 979 (1–3), 62–71. https://doi.org/10.1016/j.molstruc.2010.06.002 Musikavanhu, B., Pan, T., Ma, Q., Liang, Y., Xue, Z., Feng, L., & Zhao, L. (2024). Dual detection of Hg2+ and Pb2+ by a coumarin-functionalized Schiff base in environmental and biosystems. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy , 313 , 124101. https://doi.org/10.1016/J.SAA.2024.124101 Naureen, B., Miana, G. A., Shahid, K., Asghar, M., Tanveer, S., & Sarwar, A. (2021). Iron (III) and zinc (II) monodentate Schiff base metal complexes: Synthesis, characterisation and biological activities. Journal of Molecular Structure , 1231 , 129946. https://doi.org/10.1016/J.MOLSTRUC.2021.129946 Neupane, L. N., Kim, J. M., Lohani, C. R., & Lee, K. H. (2012). Selective and sensitive ratiometric detection of Hg2+ in 100% aqueous solution with triazole-based dansyl probe. Journal of Materials Chemistry , 22 (9), 4003–4008. https://doi.org/10.1039/C2JM15664D Pal, A. K., Ravi, R., Yadav, K. K., Jaiswal, A., Sahu, D. K., Singh, M., & Kumar, R. (2024). Novel Macrocyclic Bidentate Schiff’s base Hg (II) Complexes, Hirshfeld surface analysis, NCI analysis, and Antimicrobial activity studies. Polyhedron , 264 , 117194. https://doi.org/10.1016/J.POLY.2024.117194 Prashanthi, Y., Kiranmai, K., Subhashini, N. J. P., & Shivaraj. (2008). Synthesis, potentiometric and antimicrobial studies on metal complexes of isoxazole Schiff bases. Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy , 70 (1), 30–35. https://doi.org/10.1016/j.saa.2007.07.028 Qin, W., Long, S., Panunzio, M., Biondi, S., Molecules, S. B.-, & 2013, undefined. (2013). Schiff bases: A short survey on an evergreen chemistry tool. mdpi.com , 18 (10), 12264–12289. https://doi.org/10.3390/molecules181012264 Saddam Hossain, M., Md Zakaria, C., Kanti Roy, P., Kudrat-E-Zahan, M., Md Kudrat-E-Zahan, C., & Zakaria, C. (2018). Selected Schiff base coordination complexes and their microbial application: A review Studies on the Synthesis, Characterization and Biological Applications of Metal Schiff Base Complexes View project Synthesis and characterization of some nano-materials and investigation of their catalytic activity View project Selected Schiff base coordination complexes and their microbial application: A review. International Journal of Chemical Studies , 6 (1), 19–31. https://www.researchgate.net/publication/322202143. Accessed 12 March 2021 Saroya, S., Asija, S., Deswal, Y., Kumar, N., & Devi, J. (2023). Synthesis, Characterization, and In Vitro Antimicrobial and Antioxidant Study of the Pentacoordinated Organotin(IV) Complexes Based on Acid Hydrazide Schiff Base Ligands. Pharmaceutical Chemistry Journal , 57 (9), 1372–1383. https://doi.org/10.1007/S11094-023-03000-1 Shekhar, S., Khan, A. M., Sharma, S., Sharma, B., & Sarkar, A. (2021, June 1). Schiff base metallodrugs in antimicrobial and anticancer chemotherapy applications: a comprehensive review. Emergent Materials . Springer Nature. https://doi.org/10.1007/s42247-021-00234-1 Sidana, N., Devi, P., & Kaur, H. (2022). Thiophenol amine-based Schiff base for colorimetric detection of Cu2+ and Hg2+ ions. Optical Materials , 124 , 111985. https://doi.org/10.1016/J.OPTMAT.2022.111985 Srivastava, P., Ali, R., Razi, S. S., Shahid, M., & Misra, A. (2013). Thiourea based molecular dyad (ANTU): Fluorogenic Hg2+ selective chemodosimeter exhibiting blue-green fluorescence in aqueous-ethanol environment. Sensors and Actuators, B: Chemical , 181 , 584–595. https://doi.org/10.1016/j.snb.2013.01.080 Streets, D. G., Hao, J., Wu, Y., Jiang, J., Chan, M., Tian, H., & Feng, X. (2005). Anthropogenic mercury emissions in China. Atmospheric Environment , 39 (40), 7789–7806. https://doi.org/10.1016/J.ATMOSENV.2005.08.029 Su, Q., Niu, Q., Sun, T., & Li, T. (2016). A simple fluorescence turn-on chemosensor based on Schiff-base for Hg2+-selective detection. Tetrahedron Letters , 57 (38), 4297–4301. https://doi.org/10.1016/j.tetlet.2016.08.031 Udhayakumari, D., Suganya, S., Velmathi, S., & MubarakAli, D. (2014). Naked eye sensing of toxic metal ions in aqueous medium using thiophene-based ligands and its application in living cells. Journal of Molecular Recognition , 27 (3), 151–159. https://doi.org/10.1002/JMR.2343 Vengaian, K. M., Britto, C. D., Sekar, K., Sivaraman, G., & Singaravadivel, S. (2016). Phenothiazine-diaminomalenonitrile based Colorimetric and Fluorescence “Turn-off-on” Sensing of Hg2+ and S2−. Sensors and Actuators B: Chemical , 235 , 232–240. https://doi.org/10.1016/J.SNB.2016.04.180 Wang, Q., Kim, D., Dionysiou, D. D., Sorial, G. A., & Timberlake, D. (2004). Sources and remediation for mercury contamination in aquatic systems—a literature review. Environmental Pollution , 131 (2), 323–336. https://doi.org/10.1016/J.ENVPOL.2004.01.010 Zhong, W., Wang, L., Qin, D., Zhou, J., & Duan, H. (2020). Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg2+. ACS Omega , 5 (38), 24285–24295. https://doi.org/10.1021/ACSOMEGA.0C02481/ASSET/IMAGES/LARGE/AO0C02481_0016.JPEG Schemes Schemes 1 and 2 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Scheme1.jpg Scheme. 1Synthesis of Schiff base sensor S1. Scheme2.jpg Scheme.2 Proposed binding mode of chemosensor S1 with Hg 2+ . Cite Share Download PDF Status: Published Journal Publication published 22 Dec, 2024 Read the published version in Journal of Fluorescence → Version 1 posted Editorial decision: Revision requested 19 Nov, 2024 Reviews received at journal 18 Nov, 2024 Reviews received at journal 15 Nov, 2024 Reviewers agreed at journal 07 Nov, 2024 Reviews received at journal 07 Nov, 2024 Reviewers agreed at journal 06 Nov, 2024 Reviewers agreed at journal 05 Nov, 2024 Reviewers invited by journal 05 Nov, 2024 Editor assigned by journal 31 Oct, 2024 Submission checks completed at journal 31 Oct, 2024 First submitted to journal 23 Oct, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5316414","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":375533941,"identity":"05317178-5c1a-48f2-8012-305cb2197c2e","order_by":0,"name":"Afnan M. Alnajeebi","email":"","orcid":"","institution":"University of Jeddah","correspondingAuthor":false,"prefix":"","firstName":"Afnan","middleName":"M.","lastName":"Alnajeebi","suffix":""},{"id":375533942,"identity":"2ebc99fe-feef-497c-ac56-4364002103ee","order_by":1,"name":"Rana Yahya","email":"","orcid":"","institution":"University of Jeddah","correspondingAuthor":false,"prefix":"","firstName":"Rana","middleName":"","lastName":"Yahya","suffix":""},{"id":375533943,"identity":"eb2ceb4d-3d2d-47b3-8089-b87848b9a460","order_by":2,"name":"Alaa Shafie","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1klEQVRIie3NoQvCQBTH8SeDWU5W31B2/8KNwRT0j3kWrSajCsJWBqv7N0QwnwxmEbPNpSWDcUHBK4JpN5vhvnDwwn34AZhM/5kNMEFwPndLMkNwox8JgCjaEmfTrcqaRl5wSwQ8ljnwWDYTlGzoJ4RBWDDRyS45iDNpZiSzsVfj9KCI1YsUAQ3hslu5T8L1PlLkpQhPy2YiJIR9RkjCVqSjCFw1K37Owv6A0M+K2eKYXOZMXDUr3imu3DutuLPNd2W9HHs81ayA9XVL9Zjmv8lkMpna9AZmnjuQuEdWaAAAAABJRU5ErkJggg==","orcid":"","institution":"Taif University","correspondingAuthor":true,"prefix":"","firstName":"Alaa","middleName":"","lastName":"Shafie","suffix":""},{"id":375533944,"identity":"6e0acc07-888b-4288-aab3-0ccd71651db3","order_by":3,"name":"Amal Adnan Ashour","email":"","orcid":"","institution":"Taif University","correspondingAuthor":false,"prefix":"","firstName":"Amal","middleName":"Adnan","lastName":"Ashour","suffix":""},{"id":375533945,"identity":"6fcfc2f2-a6fc-4949-be68-bd157704928e","order_by":4,"name":"Mohammed Fareed Felemban","email":"","orcid":"","institution":"Taif University","correspondingAuthor":false,"prefix":"","firstName":"Mohammed","middleName":"Fareed","lastName":"Felemban","suffix":""},{"id":375533946,"identity":"b8807263-e800-40d9-a191-17b24483b6d5","order_by":5,"name":"Faris J Tayeb","email":"","orcid":"","institution":"University of Tabuk","correspondingAuthor":false,"prefix":"","firstName":"Faris","middleName":"J","lastName":"Tayeb","suffix":""}],"badges":[],"createdAt":"2024-10-23 07:08:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5316414/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5316414/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10895-024-04070-4","type":"published","date":"2024-12-22T15:58:05+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":69446437,"identity":"298bc0a5-30d4-45eb-a974-31fd931c29b9","added_by":"auto","created_at":"2024-11-20 12:05:51","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":48773,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eHNMR spectra of the synthesized Schiff base chemosensor \u003cstrong\u003eS1\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/a13407cc7844ac6e1502e054.jpg"},{"id":69448158,"identity":"b45cbbc7-bed3-4a64-a824-bc00e5ec316e","added_by":"auto","created_at":"2024-11-20 12:21:51","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":58947,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescence sensing response of \u003cstrong\u003eS1\u003c/strong\u003e toward different metal ions.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/a690513b386845e44c89d94d.jpg"},{"id":69446445,"identity":"42804af6-3561-4c28-aff8-a64ee26c5915","added_by":"auto","created_at":"2024-11-20 12:05:51","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":101162,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescence enhancement of \u003cstrong\u003eS1\u003c/strong\u003e upon addition of various concentration of Hg\u003csup\u003e2+\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/75676e2a9d4b92e8bd4efb1e.jpg"},{"id":69448159,"identity":"4c685fbb-cc79-4a94-853f-0fa5900859e4","added_by":"auto","created_at":"2024-11-20 12:21:51","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":27281,"visible":true,"origin":"","legend":"\u003cp\u003eCalibration curve of Hg\u003csup\u003e2+\u003c/sup\u003e concentration versus the fluorescence intensity of\u003cstrong\u003e S1\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/b9b2e7e9d0e32f2bbe85f8c9.jpg"},{"id":69447810,"identity":"c963cefa-61a0-425c-ad99-99c94517dbad","added_by":"auto","created_at":"2024-11-20 12:13:51","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":75584,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of different metal ions on the detection of Hg\u003csup\u003e2+\u003c/sup\u003e ions.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/ac747884e228790f0285e598.jpg"},{"id":69446446,"identity":"e6385217-9228-4a58-8eca-d5460fb308b8","added_by":"auto","created_at":"2024-11-20 12:05:51","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":24308,"visible":true,"origin":"","legend":"\u003cp\u003eJob's plot for the complex formed between \u003cstrong\u003eS1\u003c/strong\u003e and Hg\u003csup\u003e2+\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/2953234a907aa656b119b962.jpg"},{"id":69447809,"identity":"53f81662-bfb6-4f60-98c8-63c847f8e988","added_by":"auto","created_at":"2024-11-20 12:13:51","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":25171,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of pH on the performance of \u003cstrong\u003eS1\u003c/strong\u003e for sensing Hg\u003csup\u003e2+\u003c/sup\u003e ions.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/1926710e2a5818ef5c2e5286.jpg"},{"id":69446442,"identity":"1e0fa8ce-5f14-420a-b1c8-c6edf9dd636b","added_by":"auto","created_at":"2024-11-20 12:05:51","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":26363,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of time on the performance of \u003cstrong\u003eS1\u003c/strong\u003e for sensing Hg\u003csup\u003e2+\u003c/sup\u003e ions.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/60f41b6bbb8fe23e1d48904e.jpg"},{"id":69447808,"identity":"1f821604-f320-4b0f-b1f1-4b47e3d7b3ab","added_by":"auto","created_at":"2024-11-20 12:13:51","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":41349,"visible":true,"origin":"","legend":"\u003cp\u003eThe fluorescence response of \u003cstrong\u003eS1\u003c/strong\u003e upon the sequential addition of Hg\u003csup\u003e2+\u003c/sup\u003e and EDTA.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/81d5e8d41e1adcd45ea055f5.jpg"},{"id":72202561,"identity":"933c5301-769a-4d28-a2ba-74ac4e55b535","added_by":"auto","created_at":"2024-12-23 16:14:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1352202,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/bda1a3d1-717b-4df3-abfd-ff619099c4d3.pdf"},{"id":69446439,"identity":"c305357b-84fa-404a-8292-56795985110c","added_by":"auto","created_at":"2024-11-20 12:05:51","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":18683,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme. 1\u003c/strong\u003eSynthesis of Schiff base sensor \u003cstrong\u003eS1\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"Scheme1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/69d683383c2f977a7c8f4d66.jpg"},{"id":69447805,"identity":"852de3a6-e6ab-4008-bad6-efe2d439b013","added_by":"auto","created_at":"2024-11-20 12:13:51","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":36032,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme.2\u003c/strong\u003e Proposed binding mode of chemosensor S1 with Hg\u003csup\u003e2+\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"Scheme2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5316414/v1/bcba80236bb9ba89398e38ca.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Highly sensitive and selective detection of Hg2+ ions and antibacterial activity using a Schiff-base derivative","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSchiff bases, characterized by the presence of an imine group (-C\u0026thinsp;=\u0026thinsp;N-), have gained significant attention in recent years due to their versatility in a wide range of applications, from material science to biomedical research. (Antony et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kaushik et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Shekhar et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) These compounds are easily synthesized through the condensation of primary amines with aldehyde or ketone, and their structures can be readily modified to suit specific needs. (Qin et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) Among the numerous applications of Schiff bases, their use as fluorescence chemosensors for the detection of heavy metal ions, has garnered significant attention due to their sensitivity and selectivity. (Berhanu et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) Mercury is a highly toxic element known for its widespread environmental impact and severe health risks. It exists primarily in three forms: elemental mercury (Hg\u003csup\u003e0\u003c/sup\u003e), inorganic mercury (Hg\u003csup\u003e2+\u003c/sup\u003e), and organic mercury, particularly methylmercury (MeHg). Mercury pollution originates from both natural events, such as volcanic eruptions and forest fires, and human activities, including coal mining, fossil fuel combustion, and chemical manufacturing. Among these, industrial processes are significant contributors to the release of mercury into the atmosphere and water bodies. What makes mercury particularly dangerous is its ability to migrate easily through ecosystems, accumulate in living organisms, and target proteins in the human body due to its high affinity for thiol groups in proteins and enzymes. (Streets et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) Mercury can enter the human body through direct contact with the skin, inhalation, or ingestion, rapidly binding to thiol-containing proteins. This interaction disrupts essential physiological functions, leading to various health issues, including damage to the nervous, immune, and renal systems. In aquatic environments, elemental mercury and Hg\u003csup\u003e2+\u003c/sup\u003e can be transformed into methylmercury by microorganisms. Given the complexity of mercury behavior in biological systems and its profound health effects, there is a critical need for the development of effective chemosensor to monitor mercury contamination. (Bhardwaj et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Carocci et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Clarkson \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1997\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eSchiff base fluorescence chemosensors have emerged as a promising solution for detecting Hg\u003csup\u003e2+\u003c/sup\u003e, providing a cost-effective and rapid method for Hg\u003csup\u003e2+\u003c/sup\u003e detection with excellent selectivity and sensitivity. One of the key advantages of Schiff base sensors is their ability to serve as turn-on fluorescence sensors for Hg\u003csup\u003e2+\u003c/sup\u003e. In a typical turn-on fluorescence chemosensor, the Schiff base itself exhibits little to no fluorescence in its free form. However, upon binding to Hg\u003csup\u003e2+\u003c/sup\u003e, a significant increase in fluorescence intensity is observed. This fluorescence \"turn-on\" effect is particularly advantageous for detecting Hg\u0026sup2;⁺ in complex samples. (Behura et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Musikavanhu et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Su et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) Schiff bases containing specific functional groups, such as sulfur, nitrogen, or oxygen donors, exhibit high affinity for Hg\u003csup\u003e2+\u003c/sup\u003e due to the strong coordination between these atoms and the metal ion. This coordination alters the electronic distribution within the Schiff base, leading to the observed fluorescence enhancement. (Behura et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Feng et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Musikavanhu et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Udhayakumari et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eBeyond their role as chemosensors, Schiff bases and their metal complexes have garnered considerable interest for their antibacterial activity. The growing threat of antibiotic resistance has spurred the search for new antimicrobial agents, and Schiff bases, particularly in complexation with metal ions, have emerged as promising candidates in this regard. The antibacterial properties of Schiff base-metal complexes are largely attributed to their ability to disrupt bacterial cell membranes, inhibit enzyme activity, and interfere with vital cellular processes such as DNA replication and protein synthesis. (Abu-Dief and Mohamed \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ceramella et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) The coordination of metal ions to Schiff bases enhances the lipophilicity and stability of the resulting complexes, which facilitates their penetration into bacterial cells. Once inside the cell, Schiff base-metal complexes can interact with various biomolecules, leading to the inhibition of bacterial growth or cell death. (Al Zoubi et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Mohamed et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Naureen et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Prashanthi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Saddam Hossain et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Saroya et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) The Schiff bases complexes with Hg(II) have been shown to exhibit potent antibacterial activity, particularly against Gram-positive and Gram-negative bacteria. (Halli and Sumathi \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Pal et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eIn this study, we synthesized a Schiff-base chemosensor \u003cb\u003eS1\u003c/b\u003e and thoroughly characterized it using \u003csup\u003e1\u003c/sup\u003eHNMR and fluorescence spectroscopy. Following its synthesis, we applied \u003cb\u003eS1\u003c/b\u003e for the selective and sensitive detection of Hg\u003csup\u003e2+\u003c/sup\u003e ions, observing a significant \"turn-on\" fluorescence response due to complex formation between \u003cb\u003eS1\u003c/b\u003e and Hg\u003csup\u003e2+\u003c/sup\u003e. In addition to its sensing capabilities, we also evaluated the antibacterial activity of \u003cb\u003eS1\u003c/b\u003e and \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex against various Gram-positive and Gram-negative bacterial strains. This dual-functional approach showes the potential of \u003cb\u003eS1\u003c/b\u003e not only as an efficient chemosensor for trace-level detection of Hg\u003csup\u003e2+\u003c/sup\u003e but also as an antibacterial agent, expanding its application in both environmental monitoring and biomedical fields.\u003c/p\u003e"},{"header":"Experimental","content":"\u003ch3\u003eMaterials and methods\u003c/h3\u003e\n\u003cp\u003eThe precursors used in the preparation of the Schiff-base were obtained from reliable commercial suppliers and used without further purification. These commercially available starting materials were carefully selected to ensure high purity and consistency in the synthesis process. Methanol, acetic acid and metal salts (HgCl\u003csub\u003e2\u003c/sub\u003e, NiCl\u003csub\u003e2\u003c/sub\u003e, MgCl\u003csub\u003e2\u003c/sub\u003e, AgNO\u003csub\u003e3\u003c/sub\u003e, KCl, CuCl\u003csub\u003e2\u003c/sub\u003e, CaCl\u003csub\u003e2\u003c/sub\u003e, CoCl\u003csub\u003e2\u003c/sub\u003e, NaCl, CdCl\u003csub\u003e2\u003c/sub\u003e, CrCl\u003csub\u003e3\u003c/sub\u003e, and ZnCl\u003csub\u003e2\u003c/sub\u003e) used in this study were sourced from Sigma Aldrich and Alfa Aesar. Double-distilled water was employed in all tests. \u003cb\u003eS1\u003c/b\u003e was structurally characterized utilizing Agilent-400 DD2 NMR spectrometer (Agilent, Palo Alto, CA) to accurately analyze its functional groups and molecular composition. Fluorescence measurements were performed using a Cary Eclipse fluorescence spectrometer (Agilent Technologies, Inc., Santa Clara, California, USA) to evaluate the fluorimetric properties of \u003cb\u003eS1\u003c/b\u003e.\u003c/p\u003e\n\u003ch3\u003eSynthesis of S1\u003c/h3\u003e\n\u003cp\u003eThe Schiff base S1was prepared by combining 0.60 g (3.48 mmol) of 2-hydroxy-1-naphthaldehyde with 0.49 g (3.48 mmol) of 4-amino-6-hydroxy-2-mercaptopyrimidine in 20 mL of methanol (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The reaction mixture was refluxed for 20 hours, with its progress monitored by thin-layer chromatography (TLC) to ensure completion. After the reaction completed, the mixture was cooled to room temperature, leading to the formation of yellow precipitates. These precipitates were collected through filtration and washed several times with methanol to purify the compound. The synthesis process yielded an 90% recovery of the target product, confirming the efficiency of the method. \u003csup\u003e1\u003c/sup\u003eH-NMR (300 MHz, CDCl3, δ, ppm): 2.490 (s, 1H), 7.155 (d, 1H), 7.298 (s, 1 H), 7.468 (t, 1 H) 7.661 (t, 1 H), 7.849 (d, 1 H), 8.032 (d, 1 H), 8.403 (d,1 H), 9.506 (s, 1 H), 10.847 (s, 1 H), 13.191 (s, 1 H).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eAntibacterial activity\u003c/h3\u003e\n\u003cp\u003eThe disc diffusion method was utilized to assess the antimicrobial properties of the synthesized compounds. To maintain consistency and accuracy, bacterial suspensions were standardized to a 0.5 McFarland standard. This standardization ensured uniform bacterial inoculation on agar plates, which is crucial for minimizing variability in the results. The compounds were dissolved in 1% dimethyl sulfoxide (DMSO). The low concentration of DMSO was selected to avoid any effects on bacterial growth. For each trial, 10 \u0026micro;L of the prepared solution was applied to 6 mm antimicrobial discs, which were then placed on the inoculated agar plates and incubated at 37\u0026deg;C for 24 hours. The antimicrobial efficacy was determined by measuring the zone of inhibition. To ensure reliable data, each test was conducted in triplicate, allowing for the calculation of the mean zone of inhibition and its standard deviation, thereby enhancing the statistical significance of the findings. Positive control discs, impregnated with known antibiotics (Penicillin-Streptomycin), were included to compare the activity of the synthesized compounds with established antimicrobial agents.\u003c/p\u003e\n\u003ch3\u003eFluorescence Measurement\u003c/h3\u003e\n\u003cp\u003eThe sensing response of \u003cb\u003eS1\u003c/b\u003e was evaluated against a variety of metal ions, including transition Hg\u003csup\u003e2+\u003c/sup\u003e, Cu\u003csup\u003e2+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, Cr\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e, Cd\u003csup\u003e2+\u003c/sup\u003e, Ag\u003csup\u003e+\u003c/sup\u003e, and Na\u003csup\u003e+\u003c/sup\u003e. To establish a baseline for the sensing experiments, stock solutions of \u003cb\u003eS1\u003c/b\u003e and these metal ions were prepared at a consistent concentration of 100 ppm. This approach ensured that comparisons could be accurately made regarding the sensitivity and selectivity of \u003cb\u003eS1\u003c/b\u003e toward different metal ions. The experimental procedure involved transferring 0.20 mL of the \u003cb\u003eS1\u003c/b\u003e stock solution into a 10 ml volumetric flask, followed by the addition of 0.2 mL of the respective metal ion solution. The mixture was thoroughly shaken to promote interaction between \u003cb\u003eS1\u003c/b\u003e and the Hg\u003csup\u003e2+\u003c/sup\u003e. After allowing the solutions to equilibrate for 15 minutes at room temperature, fluorescence spectra were recorded. This incubation period was crucial, as it ensured that the systems reached a steady state, allowing for a reliable assessment of the sensing capabilities of the sensor\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStructural characterization\u003c/h2\u003e \u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH-NMR spectrum of the Schiff base \u003cb\u003eS1\u003c/b\u003e was recorded at 300 MHz in CDCl\u003csub\u003e3\u003c/sub\u003e, revealing several characteristic signals that confirm the successful formation of the target compound (\u003cb\u003eFig.\u0026nbsp;1\u003c/b\u003e). Notably, a singlet at δ 9.506 ppm is observed, which corresponds to the proton of the imine group (CH\u0026thinsp;=\u0026thinsp;N), a key indicator of Schiff base formation. This signal confirms the condensation reaction between 2-hydroxy-1-naphthaldehyde and 4-amino-6-hydroxy-2-mercaptopyrimidine, resulting in the formation of the imine bond, which is a defining feature of Schiff bases. Additionally, the presence of a singlet at δ 13.191 ppm is assigned to the hydroxyl (OH) proton of the naphthol group. The downfield shift of this signal indicates strong intramolecular hydrogen bonding between the hydroxyl group and the imine nitrogen, which is commonly observed in Schiff bases. This hydrogen bonding stabilizes the molecular structure and influences the chemical environment of the hydroxyl proton, resulting in the observed shift. Additionally, the singlet at δ 10.847 ppm is attributed to the OH proton of the pyrimidine ring. The presence of this signal indicates that the hydroxyl group is attached to the pyrimidine moiety\u003c/p\u003e \u003cp\u003eOther signals in the spectrum correspond to the aromatic protons of the naphthalene and pyrimidine ring. For example, doublets, triplets, and singlets between δ 7.155 and 8.403 ppm are assigned to these aromatic protons, reflecting the complex, conjugated structure of the Schiff base. \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFluorescence response of S1 to metal ions\u003c/h3\u003e\n\u003cp\u003eThe fluorescence properties of Schiff base \u003cb\u003eS1\u003c/b\u003e was studied toward various metal ions When excited at 350 nm, \u003cb\u003eS1\u003c/b\u003e exhibited a weak emission at 703 nm, which is attributed to the occurrence of PET within the Schiff base molecule. PET is a common mechanism in Schiff bases where the fluorescence emission is quenched due to electron transfer from the excited fluorophore to a nearby electron acceptor within the molecule, leading to low fluorescence output. This PET process is highly sensitive to external influences, such as metal ion binding, which can modulate the fluorescence response. To investigate the sensing capabilities of \u003cb\u003eS1\u003c/b\u003e, a variety of metal ions, including Hg\u003csup\u003e2+\u003c/sup\u003e, Cu\u003csup\u003e2+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, Cr\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e, Cd\u003csup\u003e2+\u003c/sup\u003e, Ag\u003csup\u003e+\u003c/sup\u003e, and Na\u003csup\u003e+\u003c/sup\u003e, were tested for their effects on the fluorescence emission of the Schiff base. Remarkably, among all the tested metal ions, Hg\u003csup\u003e2+\u003c/sup\u003e ions caused a significant enhancement in fluorescence emission (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This marked increase in fluorescence was due to the inhibition of the PET process upon \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex formation (\u003cb\u003eScheme. 2\u003c/b\u003e). The binding of Hg\u003csup\u003e2+\u003c/sup\u003e to the Schiff base effectively blocked the electron transfer pathway, thereby restoring the fluorescence of \u003cb\u003eS1\u003c/b\u003e and leading to a \"turn-on\" fluorescence response.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUpon the gradual addition of Hg\u003csup\u003e2+\u003c/sup\u003e ions from 0.01 ppm to 2 ppm, the fluorescence enhancement of the Schiff base \u003cb\u003eS1\u003c/b\u003e increased progressively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e). As the concentration of Hg\u003csup\u003e2+\u003c/sup\u003e ions rises, more \u003cb\u003eS1\u003c/b\u003e molecules interact with Hg\u003csup\u003e2+\u003c/sup\u003e, leading to a greater inhibition of PET and thus a stronger fluorescence response. The stepwise enhancement of fluorescence demonstrates the high sensitivity of \u003cb\u003eS1\u003c/b\u003e towards Hg\u003csup\u003e2+\u003c/sup\u003e detection, allowing it to accurately sense even trace amounts of Hg\u003csup\u003e2+\u003c/sup\u003e ions. This concentration-dependent fluorescence \"turn-on\" response confirms the potential of \u003cb\u003eS1\u003c/b\u003e as a reliable and sensitive probe for monitoring Hg\u003csup\u003e2+\u003c/sup\u003e levels in environmental and biological samples.\u003c/p\u003e\n\u003ch3\u003eLimit of detection\u003c/h3\u003e\n\u003cp\u003eTo assess its sensitivity, fluorescence titration experiments were performed over a concentration range of 0.01 to 2.0 ppm of Hg\u003csup\u003e2+\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The fluorescence response of \u003cb\u003eS1\u003c/b\u003e to increasing concentrations of Hg\u003csup\u003e2+\u003c/sup\u003e showed a distinct \"turn-on\" effect, attributed to the inhibition of PET upon complexation with Hg\u003csup\u003e2+\u003c/sup\u003e ion. This interaction led to a significant enhancement in fluorescence intensity, which was measured to construct a calibration plot demonstrating a direct correlation between fluorescence intensity and Hg\u003csup\u003e2+\u003c/sup\u003e concentration.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe sensitivity of \u003cb\u003eS1\u003c/b\u003e was further evaluated by calculating the limit of detection (LOD) and limit of quantification (LOQ), important parameters that define the sensor ability to detect and quantify trace amounts of analyte. The LOD, determined to be 0.002 ppm and the LOQ, calculated to be 0.008 ppm, indicate the exceptional sensitivity of the Schiff base sensor. These values were derived using the standard formula LOD\u0026thinsp;=\u0026thinsp;3σ/S and LOQ\u0026thinsp;=\u0026thinsp;10σ/S, where σ represents the standard deviation of the blank measurements, and S is the slope of the calibration curve. The low LOD and LOQ demonstrate that \u003cb\u003eS1\u003c/b\u003e can detect Hg\u003csup\u003e2+\u003c/sup\u003e at trace levels, making it a powerful tool for environmental monitoring and analytical applications.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eEffect of Foreign Metal Ions\u003c/h2\u003e \u003cp\u003eThe accurate detection of specific metal ions in complex environments is a key challenge in analytical chemistry, particularly when other metal ions are present that could interfere with the sensing process. Many metal ions coexist in natural waters, biological systems, and industrial wastes, making it essential for chemosensor to distinguish their target ion amidst various potential interferences.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn this context, evaluating the effect of foreign metal ions on the performance of a chemosensor is crucial to ensure its selectivity and reliability in real-world applications. For the selective detection of Hg\u003csup\u003e2+\u003c/sup\u003e, the chemosensor was tested in the presence of a wide range of other metal ions, including Cu\u003csup\u003e2+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, Cr\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e, Cd\u003csup\u003e2+\u003c/sup\u003e, Ag\u003csup\u003e+\u003c/sup\u003e, and Na\u003csup\u003e+\u003c/sup\u003e. These metal ions are commonly found in various environmental and biological samples and could potentially interfere with the detection of Hg\u003csup\u003e2+\u003c/sup\u003e. However, despite the introduction of these competing ions, the fluorescence response of \u003cb\u003eS1\u003c/b\u003e toward Hg\u003csup\u003e2+\u003c/sup\u003e remained unaffected, indicating a high degree of selectivity. The \u003cb\u003eS1\u003c/b\u003e sensor demonstrated a significant fluorescence enhancement upon interaction with Hg\u003csup\u003e2+\u003c/sup\u003e, whereas the presence of other metal ions resulted in negligible changes in fluorescence intensity (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e). This selectivity toward Hg\u003csup\u003e2+\u003c/sup\u003e suggests that \u003cb\u003eS1\u003c/b\u003e can function effectively in complex mixtures. It can reliably detect Hg\u003csup\u003e2+\u003c/sup\u003e without interference from other metal ions, making it suitable for practical applications in environmental monitoring, water quality analysis, and biological studies.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eJob plot analysis\u003c/h2\u003e \u003cp\u003eThe study of metal-ligand interactions is fundamental in the design of selective chemosensors for metal ion detection, and understanding the binding stoichiometry between a chemosensor and its target ion is crucial for elucidating the nature of their complexation. Schiff base chemosensors, known for their versatile coordination capabilities, often exhibit selective and strong binding with specific metal ions, leading to distinct optical or fluorescence responses. For the detection of Hg\u003csup\u003e2+\u003c/sup\u003e, determining the precise stoichiometry of the sensor-metal complex helps in understanding the sensor binding mechanism and enhancing its practical applications. The binding stoichiometry between \u003cb\u003eS1\u003c/b\u003e and Hg\u003csup\u003e2+\u003c/sup\u003e was investigated using the Job plot method. This method involves varying the molar ratio of the chemosensor to the metal ion while keeping the total concentration constant and measuring the corresponding changes in fluorescence. In the case of \u003cb\u003eS1\u003c/b\u003e and Hg\u003csup\u003e2+\u003c/sup\u003e, the Job plot exhibited a maximum value at a molar ratio of 0.5, indicating the formation of a 1:1 complex between the chemosensor and Hg\u003csup\u003e2+\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e). This 1:1 stoichiometric ratio suggests that a single molecule of \u003cb\u003eS1\u003c/b\u003e binds to one Hg\u003csup\u003e2+\u003c/sup\u003e, forming a stable complex that is responsible for the observed fluorescence \"turn-on\" effect.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003epH study\u003c/h2\u003e \u003cp\u003eThe effect of pH on the metal-binding capabilities of chemosensors, particularly Schiff base sensors, is profound. Schiff base sensors rely on functional groups such as hydroxyl and nitrogen atoms, which act as key sites for metal ion coordination. The protonation state of these groups is highly dependent on the pH of the environment, directly influencing their ability to bind metal ions. The ability of these functional groups to effectively coordinate with metal ions like is highly dependent on the pH of the solution, as the protonation or deprotonation of these sites can either facilitate or hinder binding. The fluorescence response of \u003cb\u003eS1\u003c/b\u003e to Hg\u003csup\u003e2+\u003c/sup\u003e ions was therefore studied across a wide pH range (2 to 12) to understand how pH impacts the sensor\u0026rsquo;s performance and binding efficiency. At lower pH levels (2 to 6), the fluorescence response of the SBS in the presence of Hg\u0026sup2;⁺ was minimal. This reduction in fluorescence intensity can be attributed to the protonation of the Schiff base functional groups, particularly the nitrogen atoms, which reduces their availability for coordinating with Hg\u003csup\u003e2+\u003c/sup\u003e ions. Protonated nitrogen atoms cannot effectively bind metal ions, thus hindering the formation of the sensor-metal complex. As a result, little to no fluorescence enhancement is observed at these acidic conditions. However, as the pH increases toward neutral levels (7 to 10), a significant enhancement in fluorescence is observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e). This behavior suggests that at neutral pH, the protonation is alleviated, allowing the Schiff base to efficiently coordinate with Hg\u003csup\u003e2+\u003c/sup\u003e. The deprotonated hydroxyl and nitrogen groups are now free to interact with the metal ions, forming a stable complex that results in a strong \"turn-on\" fluorescence response. This pH-dependent fluorescence enhancement reflects the optimal binding of Hg\u003csup\u003e2+\u003c/sup\u003e to the Schiff base at neutral or slightly alkaline conditions, where the metal-ligand interactions are most favorable. Interestingly, at very basic pH levels (above 10), the fluorescence intensity begins to decrease again. This drop in fluorescence can be explained by several factors. First, the competition between hydroxide ions (OH⁻) and the Schiff base for Hg\u003csup\u003e2+\u003c/sup\u003e ions becomes more pronounced at higher pH values. Hydroxide ions can bind to Hg\u003csup\u003e2+\u003c/sup\u003e, reducing the availability of free metal ions for complex formation with the Schiff base sensor. Additionally, the formation of Hg(OH)\u003csub\u003e2\u003c/sub\u003e precipitates at high pH levels further limits the concentration of free Hg\u003csup\u003e2+\u003c/sup\u003e ions in solution. This competition and potential precipitation reduce the efficiency of the chemosensor, leading to a decrease in fluorescence intensity. (Sidana et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eEffect of Time\u003c/h2\u003e \u003cp\u003eThe effect of time on the fluorescence response of the Schiff base chemosensor \u003cb\u003eS1\u003c/b\u003e to Hg\u003csup\u003e2+\u003c/sup\u003e ions was evaluated to determine the optimal duration for achieving maximum fluorescence intensity. Upon the addition of Hg\u003csup\u003e2+\u003c/sup\u003e ions to the \u003cb\u003eS1\u003c/b\u003e solution, the fluorescence intensity gradually increased with time, reaching a maximum after 15 minutes (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e). This indicates that the interaction between \u003cb\u003eS1\u003c/b\u003e and Hg\u003csup\u003e2+\u003c/sup\u003e ions, leading to the inhibition of PET and the subsequent fluorescence enhancement, occurs relatively quickly. After the 15-minute mark, the fluorescence intensity stabilized, suggesting that equilibrium between \u003cb\u003eS1\u003c/b\u003e and Hg\u003csup\u003e2+\u003c/sup\u003e had been reached, and no further increase in fluorescence was observed. This rapid response time highlights the efficiency of \u003cb\u003eS1\u003c/b\u003e as a chemosensor for detecting Hg\u003csup\u003e2+\u003c/sup\u003e ions, making it suitable for real-time monitoring applications where timely detection is crucial. Furthermore, the quick achievement of maximum fluorescence intensity ensures that the sensor can be utilized effectively in practical situations without the need for prolonged incubation times.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eReversibility study\u003c/h2\u003e \u003cp\u003eThe reversibility study of the chemosensor provides significant insights into its potential for practical applications in metal ions detection. Reusability is a key criterion for the long-term use of chemosensor, especially in environmental and industrial settings where continuous monitoring is essential. The reversible interaction between \u003cb\u003eS1\u003c/b\u003e and Hg\u003csup\u003e2+\u003c/sup\u003e ions was evaluated by alternating the addition of Hg\u003csup\u003e2+\u003c/sup\u003e ions and the chelating agent EDTA. Initially, the fluorescence intensity of \u003cb\u003eS1\u003c/b\u003e was recorded, showing weak emission at 703 nm. The addition of Hg\u003csup\u003e2+\u003c/sup\u003e ions led to a marked increase in fluorescence intensity due to the formation of the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. This fluorescence enhancement is attributed to the binding of Hg\u003csup\u003e2+\u003c/sup\u003e ions to the functional groups within \u003cb\u003eS1\u003c/b\u003e, which likely stabilizes the chemosensor structure and improves its emission properties. To test the reversibility of this sensing process, EDTA was introduced into the solution containing the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. EDTA, a well-known chelating agent with a strong affinity for metal ions, effectively stripped Hg\u003csup\u003e2+\u003c/sup\u003e from the \u003cb\u003eS1\u003c/b\u003e complex. This dissociation was reflected in a notable decrease in fluorescence intensity, indicating the successful removal of Hg\u003csup\u003e2+\u003c/sup\u003e ions from the complex. The ability of EDTA to reverse the metal binding process highlights the dynamic nature of the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e interaction and the stability of the chemosensor structure during the binding and dissociation processes. The reversibility of the system was further confirmed when additional Hg\u003csup\u003e2+\u003c/sup\u003e ions were reintroduced into the solution after EDTA treatment. The fluorescence intensity was restored to a level comparable to the initial Hg\u003csup\u003e2+\u003c/sup\u003e addition, indicating that \u003cb\u003eS1\u003c/b\u003e retained its binding capacity even after seven cycles of Hg\u003csup\u003e2+\u003c/sup\u003e complexation and dissociation (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e). This reversible behavior demonstrates that \u003cb\u003eS1\u003c/b\u003e can be used for multiple detection cycles without significant loss of performance, which is crucial for cost-effective and sustainable sensing applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eSensing mechanism\u003c/h2\u003e \u003cp\u003eThe sensing mechanism of \u003cb\u003eS1\u003c/b\u003e as a chemosensor for Hg\u003csup\u003e2+\u003c/sup\u003e ions can be explained by the PET process, which plays a key role in modulating the fluorescence response upon metal ion binding. Initially, in the absence of Hg\u003csup\u003e2+\u003c/sup\u003e ions, the fluorescence of \u003cb\u003eS1\u003c/b\u003e is weak. This weak emission is due to the PET process, where the lone pair electrons of nitrogen in the Schiff base moiety interact with the excited state of the fluorophore. In this unbound state, the nitrogen atom donates electrons to the excited fluorophore, resulting in non-radiative decay of the excited state. This quenching mechanism prevents the fluorophore from emitting fluorescence efficiently, leading to the observed weak fluorescence. When Hg\u003csup\u003e2+\u003c/sup\u003e ions are introduced, they bind to the sulfur, nitrogen and hydroxyl groups of the Schiff base. This binding effectively suppresses the PET process because the lone pair of electrons on the nitrogen is now involved in coordination with the Hg\u0026sup2;⁺ ions, making them unavailable for electron transfer to the fluorophore. The inhibition of PET restores the fluorophore ability to emit fluorescence, leading to a significant increase in fluorescence intensity upon Hg\u0026sup2;⁺ binding. This PET-based \"turn-on\" mechanism is commonly observed in chemosensors, where the metal ion binding prevents electron transfer and thus allows fluorescence emission. The fluorescence enhancement observed in \u003cb\u003eS1\u003c/b\u003e upon Hg\u0026sup2;⁺ binding is a direct result of the suppression of the PET process, indicating the formation of a stable \u003cb\u003eS1\u003c/b\u003e-Hg\u0026sup2;⁺ complex (\u003cb\u003eScheme. 2\u003c/b\u003e). Job plot analysis further confirms that the binding stoichiometry between \u003cb\u003eS1\u003c/b\u003e and Hg\u0026sup2;⁺ is 1:1, meaning that one \u003cb\u003eS1\u003c/b\u003e molecule coordinates with one Hg\u0026sup2;⁺. This strong metal-ligand interaction stabilizes the chemosensor structure, reducing vibrational and rotational motions that would otherwise lead to non-radiative decay, thereby enhancing the fluorescence intensity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003ePractical applications\u003c/h2\u003e \u003cp\u003eThe percent recovery results for Hg\u003csup\u003e2+\u003c/sup\u003e ions in real water samples, including tap, pond, and river water, demonstrate the practicality and reliability of the \u003cb\u003eS1\u003c/b\u003e chemosensor in detecting mercury in various environmental matrices. The recovery range, between 90.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27% and 104.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38%, reflects the chemosensor ability to accurately detect and quantify Hg\u003csup\u003e2+\u003c/sup\u003e ions under different real-world conditions, highlighting its sensitivity and selectivity. The recovery rates close to or slightly above 100% indicate that the \u003cb\u003eS1\u003c/b\u003e chemosensor performs well across different water samples. The slight variations in recovery values ranging from 90\u0026ndash;104% are within acceptable limits for environmental and analytical studies. These variations can be attributed to the natural complexity of environmental water samples, where factors such as pH, ionic strength, and the presence of natural organic matter may slightly influence the binding efficiency of \u003cb\u003eS1\u003c/b\u003e with Hg\u003csup\u003e2+\u003c/sup\u003e ions.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e% Recovery of Hg2+ form various water samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eConcentration of Hg\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(\u0026micro;g mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e% Recovery\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAdded\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFound\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTap water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003cp\u003e1.0\u003c/p\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003cp\u003e0.95\u003c/p\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e90.0 \u0026plusmn; 0.27\u003c/p\u003e \u003cp\u003e95.0 \u0026plusmn; 0.11\u003c/p\u003e \u003cp\u003e98.6 \u0026plusmn; 0.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRiver water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003cp\u003e1.0\u003c/p\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.46\u003c/p\u003e \u003cp\u003e0.97\u003c/p\u003e \u003cp\u003e1.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e92.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43\u003c/p\u003e \u003cp\u003e97.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e \u003cp\u003e101.3 \u0026plusmn; 0.39\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePond water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003cp\u003e1.0\u003c/p\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.48\u003c/p\u003e \u003cp\u003e1.02\u003c/p\u003e \u003cp\u003e1.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e96.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e \u003cp\u003e102.0 \u0026plusmn; 0.54\u003c/p\u003e \u003cp\u003e104.0 \u0026plusmn; 0.38\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eComparison of the Sensitivity of S1 with Reported Chemosensors\u003c/h2\u003e \u003cp\u003eThe Schiff base chemosensor \u003cb\u003eS1\u003c/b\u003e was compared with various reported chemosensors in terms of sensitivity for Hg\u003csup\u003e2+\u003c/sup\u003e detection. As shown in \u003cb\u003eTable\u0026nbsp;2, S1\u003c/b\u003e demonstrated superior sensitivity, outperforming many previously reported chemosensors.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCompression the sensing performances of chemosensors S1 with different reported chemosensors\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMethods\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eColour change\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMechanism\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLOD (\u0026micro;M)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYellow to purple\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePET\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAqueous medium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Kumar et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eColorless to pink\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eICT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e-Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e buffered solution (containing 15% methanol v/v)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Ma et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eColorless to pink\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eICT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMeCN-HEPES buffer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Dong et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2013\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDeep sky blue to blue\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eICT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.096\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.5\u0026ndash;7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAqueous\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Neupane et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2012\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYellow to green\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTICT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e-Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e buffered solution (containing 15% methanol v/v)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Ma et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCHEQ\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.084\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDMSO: H\u003csub\u003e2\u003c/sub\u003eO (1:1, v/v).\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Bhanja et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eICT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEthanol-Water (6:4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Vengaian et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2016\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eColorless to pink\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePET\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7\u0026ndash;13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDMSO/H\u003csub\u003e2\u003c/sub\u003eO (7:3, v/v, 10 \u0026micro;M)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Zhong et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGreen to blue\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eICT \u0026amp; FRET\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO/EtOH(1:1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Srivastava et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColorimetric \u0026amp; Fluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eColorless to pink\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRing-opening\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6\u0026ndash;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHEPES buffer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e(Choudhury et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFluorimetric\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePET\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCH\u003csub\u003e3\u003c/sub\u003eOH/H\u003csub\u003e2\u003c/sub\u003eO (1:9, v/v)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003ePresent work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe detection limit was notably lower, with a value of 0.002 ppm (0.01 \u0026micro;M), indicating its ability to detect trace levels of Hg\u003csup\u003e2+\u003c/sup\u003e ions with high precision. The enhanced sensitivity of \u003cb\u003eS1\u003c/b\u003e can be attributed to its strong binding affinity for Hg\u003csup\u003e2+\u003c/sup\u003e ions, which effectively inhibits PET and leads to a pronounced \"turn-on\" fluorescence response. Additionally, \u003cb\u003eS1\u003c/b\u003e ability to operate in an aqueous environment, as well as its fast response time, further emphasizes its practical advantages over other sensors that may require more complex conditions or show slower responses. This improvement in sensitivity makes \u003cb\u003eS1\u003c/b\u003e an ideal candidate for applications requiring ultra-sensitive detection of Hg\u003csup\u003e2+\u003c/sup\u003e ions, particularly in environmental monitoring and biomedical fields.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eAntibacterial activity\u003c/h2\u003e \u003cp\u003eThe data presented in the \u003cb\u003eTable. 3\u003c/b\u003e provides a comparative analysis of the antibacterial activities of \u003cb\u003eS1\u003c/b\u003e and its complex \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e, and the commonly used antibiotic combination of Penicillin-Streptomycin, against a range of bacterial strains. The bacterial strains include both Gram-negative and Gram-positive organisms, with varying susceptibilities to antibacterial agents. By analyzing the data, we can observe the performance of the \u003cb\u003eS1\u003c/b\u003e compound and its complex \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e, as well as their potential for enhancing antibacterial efficacy compared to conventional antibiotics. The inhibition zones recorded for each bacterial strain are expressed in millimeters (mm), with larger zones indicating stronger antibacterial activity. Penicillin-Streptomycin, a broad-spectrum antibiotic, generally serves as the control and benchmark for comparison. The performance of \u003cb\u003eS1\u003c/b\u003e and the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex is evaluated by comparing their inhibition zones with those produced by Penicillin-Streptomycin. Starting with \u003cem\u003ePseudomonas fluorescens\u003c/em\u003e, the inhibition zone for \u003cem\u003ePenicillin-Streptomycin\u003c/em\u003e is 19.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69 mm, while \u003cb\u003eS1\u003c/b\u003e shows a lower inhibition zone of 13.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43 mm, indicating moderate antibacterial activity. However, its complex \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e, increases the inhibition zone to 16.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.78 mm. This suggests that the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex exhibits improved antibacterial efficacy against \u003cem\u003ePseudomonas fluorescens\u003c/em\u003e compared to \u003cb\u003eS1\u003c/b\u003e. For \u003cem\u003eEscherichia coli ATCC 25922\u003c/em\u003e, a similar trend is observed. The inhibition zone for Penicillin-Streptomycin is 18.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.89 mm, while \u003cb\u003eS1\u003c/b\u003e shows a lower inhibition zone of 12.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.60 mm. However, the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex increases the inhibition zone to 15.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48 mm, again demonstrating that the complexation improves the antibacterial efficacy of \u003cb\u003eS1\u003c/b\u003e. Although the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex performs better than \u003cb\u003eS1\u003c/b\u003e, it remains slightly less effective than Penicillin-Streptomycin.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAntibacterial activity of S1 and S1-Hg2+ against various bacterial strains\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eZone of inhibition (nm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eBacterial Strains\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePenicillin-Streptomycin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003eS1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003ePseudomonas fluorescens\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.78\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eEscherichia coli\u003c/em\u003e ATCC 25922\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eBacillus cereus\u003c/em\u003e EMC 19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.28\u0026thinsp;\u0026plusmn;\u0026thinsp;1.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003ePseudomonas aeruginosa\u003c/em\u003e DSM 50071\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eBacillus subtilis\u003c/em\u003e IM 622\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eBrevibacillus brevis\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eProteus vulgaris\u003c/em\u003e FMC II\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.32 \u0026plusmn; 0.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eSalmonella typhimurium\u003c/em\u003e NRRLE 4413\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eKlebsiella pneumoniae\u003c/em\u003e EMCS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eSalmonella enterica\u003c/em\u003e ATCC 13311\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eEnterobacter aerogenes\u003c/em\u003e CCM 2531\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eStaphylococcus aureus\u003c/em\u003e 6538 P\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eBacillus megaterium\u003c/em\u003e DSM 32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the case of \u003cem\u003eBacillus cereus EMC 19\u003c/em\u003e, Penicillin-Streptomycin produces an inhibition zone of 19.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61 mm. \u003cb\u003eS1\u003c/b\u003e shows moderate activity with an inhibition zone of 14.28\u0026thinsp;\u0026plusmn;\u0026thinsp;1.06 mm, but this increases significantly to 16.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.86 mm when \u003cb\u003eS1\u003c/b\u003e is complexed with Hg(II). This represents a notable improvement in antibacterial activity, suggesting that the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex is more potent against \u003cem\u003eBacillus cereus\u003c/em\u003e than \u003cb\u003eS1\u003c/b\u003e alone. For \u003cem\u003ePseudomonas aeruginosa DSM 50071\u003c/em\u003e, the inhibition zone for Penicillin-Streptomycin is 19.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56 mm. \u003cb\u003eS1\u003c/b\u003e has an inhibition zone of 13.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76 mm, which increases to 15.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38 mm with the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. Similar to previous observations, the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex enhances the antibacterial activity compared to \u003cb\u003eS1\u003c/b\u003e, though it does not exceed the effectiveness of Penicillin-Streptomycin. For \u003cem\u003eBacillus subtilis IM 622\u003c/em\u003e, the inhibition zone for Penicillin-Streptomycin is 20.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.70 mm. \u003cb\u003eS1\u003c/b\u003e shows relatively strong activity with an inhibition zone of 14.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57 mm, but this increases to 17.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76 mm when complexed with Hg(II). In the case of \u003cem\u003eBrevibacillus brevis\u003c/em\u003e, Penicillin-Streptomycin shows an inhibition zone of 19.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66 mm. The inhibition zone for \u003cb\u003eS1\u003c/b\u003e is 13.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46 mm, which increases to 15.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.72 mm with the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. For \u003cem\u003eProteus vulgaris FMC II\u003c/em\u003e, Penicillin-Streptomycin produces an inhibition zone of 17.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61 mm. \u003cb\u003eS1\u003c/b\u003e exhibits relatively weak activity with an inhibition zone of 10.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41 mm, but this increases to 13.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55 mm when \u003cb\u003eS1\u003c/b\u003e form complex. For \u003cem\u003eSalmonella typhimurium NRRLE 4413\u003c/em\u003e, Penicillin-Streptomycin produces an inhibition zone of 18.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29 mm. \u003cb\u003eS1\u003c/b\u003e shows moderate activity with an inhibition zone of 11.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.87 mm, which increases to 14.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.98 mm with the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. For \u003cem\u003eKlebsiella pneumoniae EMCS\u003c/em\u003e, the inhibition zone for Penicillin-Streptomycin is 17.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62 mm. \u003cb\u003eS1\u003c/b\u003e shows weak activity with an inhibition zone of 10.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.70 mm, but the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex improves this to 15.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69 mm. This significant increase in inhibition zone indicates that the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex is much more effective than \u003cb\u003eS1\u003c/b\u003e alone against \u003cem\u003eKlebsiella pneumoniae\u003c/em\u003e. For \u003cem\u003eSalmonella enterica ATCC 13311\u003c/em\u003e, Penicillin-Streptomycin produces an inhibition zone of 17.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22 mm. \u003cb\u003eS1\u003c/b\u003e has an inhibition zone of 11.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59 mm, which increases to 13.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.71 mm with the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. The improvement in antibacterial activity following complexation is modest but notable. For \u003cem\u003eEnterobacter aerogenes CCM 2531\u003c/em\u003e, Penicillin-Streptomycin produces an inhibition zone of 19.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61 mm. \u003cb\u003eS1\u003c/b\u003e shows moderate activity with an inhibition zone of 12.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11 mm, which increases to 15.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.60 mm with the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. This represents a significant enhancement in antibacterial activity, suggesting that the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex could be a promising candidate for further development in targeting \u003cem\u003eEnterobacter aerogenes\u003c/em\u003e. For \u003cem\u003eStaphylococcus aureus 6538 P\u003c/em\u003e, Penicillin-Streptomycin shows an inhibition zone of 18.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46 mm. \u003cb\u003eS1\u003c/b\u003e exhibits moderate activity with an inhibition zone of 13.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49 mm, but this only increases slightly to 14.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27 mm with the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. Finally, for \u003cem\u003eBacillus megaterium DSM 32\u003c/em\u003e, Penicillin-Streptomycin produces an inhibition zone of 18.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.92 mm. \u003cb\u003eS1\u003c/b\u003e shows moderate activity with an inhibition zone of 12.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77 mm, which increases to 15.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58 mm with the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex. This significant improvement suggests that the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex is more effective than \u003cb\u003eS1\u003c/b\u003e alone.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eSchiff-base chemosensor \u003cb\u003eS1\u003c/b\u003e synthesized in this study has proven to be a highly selective and sensitive tool for detecting Hg\u003csup\u003e2+\u003c/sup\u003e ions. Its 'turn-on' fluorescence response, attributed to the suppression of PET upon complex formation with Hg\u003csup\u003e2+\u003c/sup\u003e, enabled efficient detection at trace levels with a remarkably low detection limit of 0.002 ppm. The simplicity of its design and the high sensitivity make \u003cb\u003eS1\u003c/b\u003e a valuable candidate for practical applications in monitoring Hg\u003csup\u003e2+\u003c/sup\u003e contamination, especially in environmental settings where detecting trace amounts of toxic metals is crucial for public health and safety. Additionally, the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex exhibited excellent antibacterial activity against both Gram-positive and Gram-negative bacterial strains, demonstrating its potential as a multifunctional system. This dual capability not only enhances the utility of \u003cb\u003eS1\u003c/b\u003e in Hg\u003csup\u003e2+\u003c/sup\u003e detection but also extends its applications into the biomedical field, where antibacterial agents are in demand. The combination of environmental sensing and antibacterial activity positions \u003cb\u003eS1\u003c/b\u003e as a promising candidate for future developments in environmental monitoring and biomedical technologies, providing a platform for further exploration of Schiff-base chemosensors in multifunctional systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors extend their appreciation to Taif University, Saudi Arabia for supporting this work through project number (TU-DSPP-2024-58)\u0026rdquo;.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research was funded by Taif University, Saudi Arabia, Project Number (TU-DSPP-2024-58)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e: All data generated or analyzed during this study are included in this published article\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode Availability:\u003c/strong\u003e ChemDraw\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e: This article does not contain any studies with human participants or animals, clinical trial registration, or plant reproducibility performed by any authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish:\u003c/strong\u003e The authors have approved the paper and agree with its publication.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e: \u0026nbsp;No applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contributions:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAfnan M. Alnajeebi: Conceptualization-Equal, Editing-Equal,\u0026nbsp;Rana Yahya, Editing-Equal, Formal analysis-Equal,\u0026nbsp;Dr Alaa Shafie:\u0026nbsp;Supervision-Equal, Writing Original Draft-Equal,\u0026nbsp;Dr Amal Adnan Ashour:\u0026nbsp;Data Curation-Equal, Visualization-Equal,\u0026nbsp;Dr Mohammed Fareed Felemban:\u0026nbsp;Data Curation-Equal, Editing-Equal,\u0026nbsp;Dr Faris J. Tayeb:\u0026nbsp;Visualization-Equal, Formal analysis-Equal,\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest:\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no conflicts of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbu-Dief, A. M., \u0026amp; Mohamed, I. M. A. (2015). A review on versatile applications of transition metal complexes incorporating Schiff bases. \u003cem\u003eBeni-Suef University Journal of Basic and Applied Sciences\u003c/em\u003e, \u003cem\u003e4\u003c/em\u003e(2), 119\u0026ndash;133. https://doi.org/10.1016/J.BJBAS.2015.05.004\u003c/li\u003e\n\u003cli\u003eAl Zoubi, W., Al-Hamdani, A. A. S., Putu Widiantara, I., Hamoodah, R. G., \u0026amp; Ko, Y. G. (2017). Theoretical studies and antibacterial activity for Schiff base complexes. \u003cem\u003eJournal of Physical Organic Chemistry\u003c/em\u003e, \u003cem\u003e30\u003c/em\u003e(12), e3707. https://doi.org/10.1002/POC.3707\u003c/li\u003e\n\u003cli\u003eAntony, R., Arun, T., \u0026amp; Manickam, S. T. D. (2019). A review on applications of chitosan-based Schiff bases. \u003cem\u003eInternational Journal of Biological Macromolecules\u003c/em\u003e, \u003cem\u003e129\u003c/em\u003e, 615\u0026ndash;633. https://doi.org/10.1016/J.IJBIOMAC.2019.02.047\u003c/li\u003e\n\u003cli\u003eBehura, R., Mohanty, P., Sahu, G., Dash, P. P., Behera, S., Dinda, R., et al. (2023). A highly selective Schiff base fluorescent sensor for Zn2+, Cd2+ and Hg2+ based on 2,4-dinitrophenylhydrazine derivative. \u003cem\u003eInorganic Chemistry Communications\u003c/em\u003e, \u003cem\u003e154\u003c/em\u003e, 110959. https://doi.org/10.1016/J.INOCHE.2023.110959\u003c/li\u003e\n\u003cli\u003eBerhanu, A. L., Gaurav, Mohiuddin, I., Malik, A. K., Aulakh, J. S., Kumar, V., \u0026amp; Kim, K. H. A review of the applications of Schiff bases as optical chemical sensors. , 116 TrAC - Trends in Analytical Chemistry 74\u0026ndash;91 (2019). Elsevier B.V. https://doi.org/10.1016/j.trac.2019.04.025\u003c/li\u003e\n\u003cli\u003eBhanja, A., Pandey, P., \u0026amp; Murugavel, R. (2024). Carbazole based Schiff base ligand: An efficient \u0026ldquo;Turn-on/off\u0026rdquo; sensor for the detection of Al3+ and F\u0026minus; ions and \u0026ldquo;Turn-off\u0026rdquo; sensor for Hg2+ ion. \u003cem\u003eJournal of Photochemistry and Photobiology A: Chemistry\u003c/em\u003e, \u003cem\u003e447\u003c/em\u003e, 115269. https://doi.org/10.1016/J.JPHOTOCHEM.2023.115269\u003c/li\u003e\n\u003cli\u003eBhardwaj, V., Nurchi, V. M., \u0026amp; Sahoo, S. K. (2021). Mercury Toxicity and Detection Using Chromo-Fluorogenic Chemosensors. \u003cem\u003ePharmaceuticals 2021, Vol. 14, Page 123\u003c/em\u003e, \u003cem\u003e14\u003c/em\u003e(2), 123. https://doi.org/10.3390/PH14020123\u003c/li\u003e\n\u003cli\u003eCarocci, A., Rovito, N., Sinicropi, M. S., \u0026amp; Genchi, G. (2014). Mercury toxicity and neurodegenerative effects. \u003cem\u003eReviews of Environmental Contamination and Toxicology\u003c/em\u003e, \u003cem\u003e229\u003c/em\u003e, 1\u0026ndash;18. https://doi.org/10.1007/978-3-319-03777-6_1/COVER\u003c/li\u003e\n\u003cli\u003eCeramella, J., Iacopetta, D., Catalano, A., Cirillo, F., Lappano, R., \u0026amp; Sinicropi, M. S. (2022). A Review on the Antimicrobial Activity of Schiff Bases: Data Collection and Recent Studies. \u003cem\u003eAntibiotics 2022, Vol. 11, Page 191\u003c/em\u003e, \u003cem\u003e11\u003c/em\u003e(2), 191. https://doi.org/10.3390/ANTIBIOTICS11020191\u003c/li\u003e\n\u003cli\u003eChoudhury, N., Ruidas, B., Mukhopadhyay, C. Das, \u0026amp; De, P. (2020). Rhodamine-Appended Polymeric Probe: An Efficient Colorimetric and Fluorometric Sensing Platform for Hg2+in Aqueous Medium and Living Cells. \u003cem\u003eACS Applied Polymer Materials\u003c/em\u003e, \u003cem\u003e2\u003c/em\u003e(11), 5077\u0026ndash;5085. https://doi.org/10.1021/ACSAPM.0C00878/SUPPL_FILE/AP0C00878_SI_001.PDF\u003c/li\u003e\n\u003cli\u003eClarkson, T. W. (1997). The Toxicology of Mercury. \u003cem\u003eCritical Reviews in Clinical Laboratory Sciences\u003c/em\u003e, \u003cem\u003e34\u003c/em\u003e(4), 369\u0026ndash;403. https://doi.org/10.3109/10408369708998098\u003c/li\u003e\n\u003cli\u003eDong, Z., Tian, X., Chen, Y., Hou, J., Guo, Y., Sun, J., \u0026amp; Ma, J. (2013). A highly selective fluorescent chemosensor for Hg2+ based on rhodamine B and its application as a molecular logic gate. \u003cem\u003eDyes and Pigments\u003c/em\u003e, \u003cem\u003e97\u003c/em\u003e(2), 324\u0026ndash;329. https://doi.org/10.1016/J.DYEPIG.2013.01.002\u003c/li\u003e\n\u003cli\u003eFeng, L., Shi, W., Ma, J., Chen, Y., Kui, F., Hui, Y., \u0026amp; Xie, Z. (2016, December 1). A novel thiosemicarbazone Schiff base derivative with aggregation-induced emission enhancement characteristics and its application in Hg2+ detection. \u003cem\u003eSensors and Actuators, B: Chemical\u003c/em\u003e. Elsevier B.V. https://doi.org/10.1016/j.snb.2016.06.129\u003c/li\u003e\n\u003cli\u003eHalli, M. B., \u0026amp; Sumathi, R. B. (2012). Synthesis, spectroscopic, antimicrobial and DNA cleavage studies of new Co(II), Ni(II), Cu(II), Cd(II), Zn(II) and Hg(II) complexes with naphthofuran-2-carbohydrazide Schiff base. \u003cem\u003eJournal of Molecular Structure\u003c/em\u003e, \u003cem\u003e1022\u003c/em\u003e, 130\u0026ndash;138. https://doi.org/10.1016/J.MOLSTRUC.2012.05.003\u003c/li\u003e\n\u003cli\u003eKaushik, S., Paliwal, S. K., Iyer, M. R., \u0026amp; Patil, V. M. (2023). Promising Schiff bases in antiviral drug design and discovery. \u003cem\u003eMedicinal Chemistry Research 2023 32:6\u003c/em\u003e, \u003cem\u003e32\u003c/em\u003e(6), 1063\u0026ndash;1076. https://doi.org/10.1007/S00044-023-03068-0\u003c/li\u003e\n\u003cli\u003eKumar, A., Hur, W., Seong, G. H., Kumar, S., \u0026amp; Chae, P. S. (2022). Chromofluorogenic naphthoquinolinedione-based probes for sensitive detection and removal of Hg2+ in aqueous solutions. \u003cem\u003eDyes and Pigments\u003c/em\u003e, \u003cem\u003e198\u003c/em\u003e, 110025. https://doi.org/10.1016/J.DYEPIG.2021.110025\u003c/li\u003e\n\u003cli\u003eMa, L. J., Liu, J., Deng, L., Zhao, M., Deng, Z., Li, X., et al. (2014). Selective and sensitive fluorescence-shift probes based on two dansyl groups for mercury(II) ion detection. \u003cem\u003ePhotochemical \u0026amp; Photobiological Sciences\u003c/em\u003e, \u003cem\u003e13\u003c/em\u003e(11), 1521\u0026ndash;1528. https://doi.org/10.1039/C4PP00094C\u003c/li\u003e\n\u003cli\u003eMohamed, G. G., Zayed, M. A., \u0026amp; Abdallah, S. M. (2010). Metal complexes of a novel Schiff base derived from sulphametrole and varelaldehyde. Synthesis, spectral, thermal characterization and biological activity. \u003cem\u003eJournal of Molecular Structure\u003c/em\u003e, \u003cem\u003e979\u003c/em\u003e(1\u0026ndash;3), 62\u0026ndash;71. https://doi.org/10.1016/j.molstruc.2010.06.002\u003c/li\u003e\n\u003cli\u003eMusikavanhu, B., Pan, T., Ma, Q., Liang, Y., Xue, Z., Feng, L., \u0026amp; Zhao, L. (2024). Dual detection of Hg2+ and Pb2+ by a coumarin-functionalized Schiff base in environmental and biosystems. \u003cem\u003eSpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy\u003c/em\u003e, \u003cem\u003e313\u003c/em\u003e, 124101. https://doi.org/10.1016/J.SAA.2024.124101\u003c/li\u003e\n\u003cli\u003eNaureen, B., Miana, G. A., Shahid, K., Asghar, M., Tanveer, S., \u0026amp; Sarwar, A. (2021). Iron (III) and zinc (II) monodentate Schiff base metal complexes: Synthesis, characterisation and biological activities. \u003cem\u003eJournal of Molecular Structure\u003c/em\u003e, \u003cem\u003e1231\u003c/em\u003e, 129946. https://doi.org/10.1016/J.MOLSTRUC.2021.129946\u003c/li\u003e\n\u003cli\u003eNeupane, L. N., Kim, J. M., Lohani, C. R., \u0026amp; Lee, K. H. (2012). Selective and sensitive ratiometric detection of Hg2+ in 100% aqueous solution with triazole-based dansyl probe. \u003cem\u003eJournal of Materials Chemistry\u003c/em\u003e, \u003cem\u003e22\u003c/em\u003e(9), 4003\u0026ndash;4008. https://doi.org/10.1039/C2JM15664D\u003c/li\u003e\n\u003cli\u003ePal, A. K., Ravi, R., Yadav, K. K., Jaiswal, A., Sahu, D. K., Singh, M., \u0026amp; Kumar, R. (2024). Novel Macrocyclic Bidentate Schiff\u0026rsquo;s base Hg (II) Complexes, Hirshfeld surface analysis, NCI analysis, and Antimicrobial activity studies. \u003cem\u003ePolyhedron\u003c/em\u003e, \u003cem\u003e264\u003c/em\u003e, 117194. https://doi.org/10.1016/J.POLY.2024.117194\u003c/li\u003e\n\u003cli\u003ePrashanthi, Y., Kiranmai, K., Subhashini, N. J. P., \u0026amp; Shivaraj. (2008). Synthesis, potentiometric and antimicrobial studies on metal complexes of isoxazole Schiff bases. \u003cem\u003eSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy\u003c/em\u003e, \u003cem\u003e70\u003c/em\u003e(1), 30\u0026ndash;35. https://doi.org/10.1016/j.saa.2007.07.028\u003c/li\u003e\n\u003cli\u003eQin, W., Long, S., Panunzio, M., Biondi, S., Molecules, S. B.-, \u0026amp; 2013, undefined. (2013). Schiff bases: A short survey on an evergreen chemistry tool. \u003cem\u003emdpi.com\u003c/em\u003e, \u003cem\u003e18\u003c/em\u003e(10), 12264\u0026ndash;12289. https://doi.org/10.3390/molecules181012264\u003c/li\u003e\n\u003cli\u003eSaddam Hossain, M., Md Zakaria, C., Kanti Roy, P., Kudrat-E-Zahan, M., Md Kudrat-E-Zahan, C., \u0026amp; Zakaria, C. (2018). Selected Schiff base coordination complexes and their microbial application: A review Studies on the Synthesis, Characterization and Biological Applications of Metal Schiff Base Complexes View project Synthesis and characterization of some nano-materials and investigation of their catalytic activity View project Selected Schiff base coordination complexes and their microbial application: A review. \u003cem\u003eInternational Journal of Chemical Studies\u003c/em\u003e, \u003cem\u003e6\u003c/em\u003e(1), 19\u0026ndash;31. https://www.researchgate.net/publication/322202143. Accessed 12 March 2021\u003c/li\u003e\n\u003cli\u003eSaroya, S., Asija, S., Deswal, Y., Kumar, N., \u0026amp; Devi, J. (2023). Synthesis, Characterization, and In Vitro Antimicrobial and Antioxidant Study of the Pentacoordinated Organotin(IV) Complexes Based on Acid Hydrazide Schiff Base Ligands. \u003cem\u003ePharmaceutical Chemistry Journal\u003c/em\u003e, \u003cem\u003e57\u003c/em\u003e(9), 1372\u0026ndash;1383. https://doi.org/10.1007/S11094-023-03000-1\u003c/li\u003e\n\u003cli\u003eShekhar, S., Khan, A. M., Sharma, S., Sharma, B., \u0026amp; Sarkar, A. (2021, June 1). Schiff base metallodrugs in antimicrobial and anticancer chemotherapy applications: a comprehensive review. \u003cem\u003eEmergent Materials\u003c/em\u003e. Springer Nature. https://doi.org/10.1007/s42247-021-00234-1\u003c/li\u003e\n\u003cli\u003eSidana, N., Devi, P., \u0026amp; Kaur, H. (2022). Thiophenol amine-based Schiff base for colorimetric detection of Cu2+ and Hg2+ ions. \u003cem\u003eOptical Materials\u003c/em\u003e, \u003cem\u003e124\u003c/em\u003e, 111985. https://doi.org/10.1016/J.OPTMAT.2022.111985\u003c/li\u003e\n\u003cli\u003eSrivastava, P., Ali, R., Razi, S. S., Shahid, M., \u0026amp; Misra, A. (2013). Thiourea based molecular dyad (ANTU): Fluorogenic Hg2+ selective chemodosimeter exhibiting blue-green fluorescence in aqueous-ethanol environment. \u003cem\u003eSensors and Actuators, B: Chemical\u003c/em\u003e, \u003cem\u003e181\u003c/em\u003e, 584\u0026ndash;595. https://doi.org/10.1016/j.snb.2013.01.080\u003c/li\u003e\n\u003cli\u003eStreets, D. G., Hao, J., Wu, Y., Jiang, J., Chan, M., Tian, H., \u0026amp; Feng, X. (2005). Anthropogenic mercury emissions in China. \u003cem\u003eAtmospheric Environment\u003c/em\u003e, \u003cem\u003e39\u003c/em\u003e(40), 7789\u0026ndash;7806. https://doi.org/10.1016/J.ATMOSENV.2005.08.029\u003c/li\u003e\n\u003cli\u003eSu, Q., Niu, Q., Sun, T., \u0026amp; Li, T. (2016). A simple fluorescence turn-on chemosensor based on Schiff-base for Hg2+-selective detection. \u003cem\u003eTetrahedron Letters\u003c/em\u003e, \u003cem\u003e57\u003c/em\u003e(38), 4297\u0026ndash;4301. https://doi.org/10.1016/j.tetlet.2016.08.031\u003c/li\u003e\n\u003cli\u003eUdhayakumari, D., Suganya, S., Velmathi, S., \u0026amp; MubarakAli, D. (2014). Naked eye sensing of toxic metal ions in aqueous medium using thiophene-based ligands and its application in living cells. \u003cem\u003eJournal of Molecular Recognition\u003c/em\u003e, \u003cem\u003e27\u003c/em\u003e(3), 151\u0026ndash;159. https://doi.org/10.1002/JMR.2343\u003c/li\u003e\n\u003cli\u003eVengaian, K. M., Britto, C. D., Sekar, K., Sivaraman, G., \u0026amp; Singaravadivel, S. (2016). Phenothiazine-diaminomalenonitrile based Colorimetric and Fluorescence \u0026ldquo;Turn-off-on\u0026rdquo; Sensing of Hg2+ and S2\u0026minus;. \u003cem\u003eSensors and Actuators B: Chemical\u003c/em\u003e, \u003cem\u003e235\u003c/em\u003e, 232\u0026ndash;240. https://doi.org/10.1016/J.SNB.2016.04.180\u003c/li\u003e\n\u003cli\u003eWang, Q., Kim, D., Dionysiou, D. D., Sorial, G. A., \u0026amp; Timberlake, D. (2004). Sources and remediation for mercury contamination in aquatic systems\u0026mdash;a literature review. \u003cem\u003eEnvironmental Pollution\u003c/em\u003e, \u003cem\u003e131\u003c/em\u003e(2), 323\u0026ndash;336. https://doi.org/10.1016/J.ENVPOL.2004.01.010\u003c/li\u003e\n\u003cli\u003eZhong, W., Wang, L., Qin, D., Zhou, J., \u0026amp; Duan, H. (2020). Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg2+. \u003cem\u003eACS Omega\u003c/em\u003e, \u003cem\u003e5\u003c/em\u003e(38), 24285\u0026ndash;24295. https://doi.org/10.1021/ACSOMEGA.0C02481/ASSET/IMAGES/LARGE/AO0C02481_0016.JPEG\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eSchemes 1 and 2 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Schiff-base, Chemosensor, Turn-on, PET, Complex, Biomedical applications","lastPublishedDoi":"10.21203/rs.3.rs-5316414/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5316414/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA simple and highly effective Schiff-base fluorescent chemosensor (\u003cb\u003eS1\u003c/b\u003e) was synthesized and characterized by \u003csup\u003e1\u003c/sup\u003eHNMR and fluorescence spectroscopy. The synthesized chemosensor was applied for the selective and sensitive detection of Hg\u003csup\u003e2+\u003c/sup\u003e ions. The chemosensor exhibited a strong 'turn-on' fluorescence response in a CH\u003csub\u003e3\u003c/sub\u003eOH/H\u003csub\u003e2\u003c/sub\u003eO (1:9, v/v) solution due to complex formation (\u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e) which block photo induce electron transfer (PET). The chemosensor showed significant sensitivity with very low detection limit of 0.002 ppm, making it suitable for trace-level Hg\u003csup\u003e2+\u003c/sup\u003e detection. Furthermore, the \u003cb\u003eS1-Hg\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex demonstrated excellent antibacterial activity against various Gram-positive and Gram-negative bacterial strains, broadening its utility beyond sensing. This dual-functional system offers significant potential in environmental and biomedical applications.\u003c/p\u003e","manuscriptTitle":"Highly sensitive and selective detection of Hg2+ ions and antibacterial activity using a Schiff-base derivative","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-20 12:05:46","doi":"10.21203/rs.3.rs-5316414/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-11-19T13:27:07+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-18T14:47:20+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-15T16:10:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8887014051668238571276481651372053945","date":"2024-11-08T02:23:37+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-07T21:04:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"76678282823454917776411580938351398060","date":"2024-11-06T07:55:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"277032869694603692171802687057745122185","date":"2024-11-05T17:41:51+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-05T17:31:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-31T12:07:32+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-31T12:04:01+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Fluorescence","date":"2024-10-23T06:54:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5ca9214b-89b8-4604-b4bc-8c3880bdcb5a","owner":[],"postedDate":"November 20th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-23T16:08:18+00:00","versionOfRecord":{"articleIdentity":"rs-5316414","link":"https://doi.org/10.1007/s10895-024-04070-4","journal":{"identity":"journal-of-fluorescence","isVorOnly":false,"title":"Journal of Fluorescence"},"publishedOn":"2024-12-22 15:58:05","publishedOnDateReadable":"December 22nd, 2024"},"versionCreatedAt":"2024-11-20 12:05:46","video":"","vorDoi":"10.1007/s10895-024-04070-4","vorDoiUrl":"https://doi.org/10.1007/s10895-024-04070-4","workflowStages":[]},"version":"v1","identity":"rs-5316414","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5316414","identity":"rs-5316414","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}