Environment-friendly lead-free Cs3Bi2Br9 perovskite quantum dots as fluorescent probes for rapid detection of oxytetracycline via inner filter effect

Environment-friendly lead-free Cs3Bi2Br9 perovskite quantum dots as fluorescent probes for rapid detection of oxytetracycline via inner filter effect | 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 Environment-friendly lead-free Cs3Bi2Br9 perovskite quantum dots as fluorescent probes for rapid detection of oxytetracycline via inner filter effect Jiali Liu, Chen Li, Shen Zhang, Xinni Liu, Xiao Wei, Yue Gao, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4918535/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract All-inorganic perovskite quantum dots have sparked a research boom due to their excellent optical properties, however, their own strong ionicity and lead toxicity have hindered further development in the field of sensing. In this study, we have solved the toxicity problem of lead-based perovskite quantum dots by replacing lead with green metal bismuth. Meanwhile, due to the ligand-passivation effect of oleylamine and oleic acid, we successfully synthesized highly stable bismuth-based perovskite quantum dots(Cs 3 Bi 2 Br 9 PQDs)in ethanol, and constructed the environment-friendly fluorescence sensor for the quantitative detection of OTC for the first time. The results demonstrated that the fluorescence quenching degree of Cs 3 Bi 2 Br 9 PQDs showed a good linear relationship with the concentration of OTC within the range of 2.0 ~ 18 µM, and the detection limit was 0.432 µM. By studying fluorescence lifetime, absorption spectroscopy, and evaluation of internal filtration parameters., it was proved that the sensing mechanism is caused by the inner filter effect owing to the overlapping of fluorescence emission spectrum of Cs 3 Bi 2 Br 9 PQDs and UV absorption spectrum of OTC. Moreover, Cs 3 Bi 2 Br 9 PQDs fluorescent sensor had good selectivity and anti-interference ability. It is believed that this work will open up a new way for lead-free perovskite quantum dot fluorescence sensor in the field of analytical detection. bismuth perovskite quantum dots oxytetracycline fluorescence detection inner filter effect Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 1. Introduction Oxytetracycline (OTC), as an antimicrobial compound, is extensively utilized in medicine, animal husbandry and aquaculture due to its cost-effectiveness and broad spectrum [1, 2] . However, OTC is difficult to be adsorbed and degraded in the animal body, and most of it will enter into excreta (faeces, urine, etc.) and discharged wastes in the form of original and intermediate products, which causes serious pollution in the ecological environment [3] . In addition, excessive use of OTC can lead to high levels of residues in animal-derived food, posing a serious threat to human health by causing liver damage, bone disorders, gastrointestinal issues, and renal dysfunction [4, 5] . Studies have demonstrated that OTC has been detected in drinking water and food products (milk, meat and honey, etc.) [6, 7] . Therefore, it is crucial to monitor and detect residual OTC levels in animal-derived foods and aquatic environments for the sake of human health. Currently available methods for determining residual levels of OTC include high-performance liquid chromatography (HPLC) [8] , microbial [9] and electrochemical methods [10] . But these methods have the drawbacks including lengthy operation time, extensive pre-treatment steps, costliness and high reagent consumption [11–13] . Hence, it is imminent to develop a method with easy-to-operate, rapid, and highly selective to detect residual OTC. In recent years, fluorescent sensors prepared with quantum dots (QDs) as fluorescent groups have achieved the advantages of simple operation, low cost, good sensitivity and selectivity, and good stability. So far, QDs have been used for the detection of various pollutants, such as tetracycline [14] , dopamine [15] , sulfonamides [16] , organophosphorus pesticides [17] , etc. However, traditional quantum dots (CdTe QDs, Si QDs, ZnS QDs, etc.) mostly have defects including expensive reagents and weak luminous intensity. These limitations prevent them from meeting the requirements of highly sensitive analysis detection. Since the first report of perovskite quantum dots (PQDs), they have received extensive attention from researchers for their high photoluminescence quantum yield (PLQY > 90%), narrower full width at half-maximum (FWHM:12–25 nm) and tunable emission wavelength. PQDs have great development potential in solar energy [18] , light-emitting diode [19] , laser [20] , fluorescence detection [21] and other fields. In recent years, fluorescent sensors constructed with PQDs as fluorescent groups have been used for the detection of heavy metal ions [22] , organics [23] , gases [24] and anions [25] . Nevertheless, most of these detections were performed in non-polar solvents, because the strong ionic nature of PQDs renders them extremely sensitive to the external environment [26] . Additionally, lead-based PQDs contain lead element which is one of the three major heavy metal pollutants, it accumulates through food chains due to its bioaccumulation ability and non-degradability thereby polluting the environment. When the lead content in human body reaches a certain level, it can cause fatigue, muscle weakness, clumsiness, and confusion [27] . Therefore, how to overcome the stability and toxicity problems has become a must for the green and sustainable development of PQDs. At present, in order to effectively reduce the impact of PQDs toxicity on the environment, it is an effective strategy to encapsulate Pb 2+ into a tightly structured polymer matrix to reduce the diffusion of Pb 2+ in the environment. Zhang et al. [28] synthesized a stable CsPbBr 3 /polypyrrole (PPy) composite by photocatalytic polymerization, and PQDs were encapsulated in the PPy protective layer to reduce the environmental impact of Pb 2+ toxicity to a certain extent. However, this method cannot essentially eliminate the environmental hazards of lead-based PQDs. In addition to this, it has been mentioned in the literature to prepare environmentally friendly perovskite quantum dots using non-toxic metals such as tin (Sn) instead of lead (Pb) [29] , CsSnX 3 prepared using divalent tin was highly susceptible to conditions such as light and temperature, which is due to the fact that Sn(II) can be oxidized very easily to Sn(IV). The PLQY of CsSnX 3 is much lower than Pb-based analogues [30] . Trivalent bismuth is harmless to human body and is a kind of "green metal" that shares many similar properties with lead, such as isoelectronic structure (6s 2 6p 0 ) and similar ionic radius(Bi 3+ :1.03Å, Pb 2+ :1.19Å), and is more stable than tin. So bismuth is the best candidate material for preparing non-toxic perovskite materials. Herein, environment-friendly lead-free Cs 3 Bi 2 Br 9 PQDs were synthesized as a fluorescent sensor by using ligand-assisted reprecipitation method with OA and OAm as ligands, which achieves high sensitivity detection of trace OTC in ethanol based on the inner filter effect. The synthesized Cs 3 Bi 2 Br 9 PQDs can not only be stably dispersed in the ethanol phase, but we used the green metal-bismuth element to replace the lead element, effectively avoiding the secondary pollution to the environment. In addition, the structure, properties, detection conditions and quenching mechanism of Cs 3 Bi 2 Br 9 PQDs were characterized and studied in detail, and the obtained fluorescence sensor was successfully used for OTC detection of soil samples. 2. Experimental section 2.1 Chemicals and materials All chemicals were analytical reagent grade and used as received without any further purification. Bismuth bromide (BiBr 3 ), cesium bromide (CsBr), dimethyl sulfoxide (DMSO), polyethylene glycol 200 (PEG), ethyl acetate (EAC), 2,4,6-trichlorophenol (2,4,6-TCP), o-phenylenediamine (OPD), sulphamethoxazole (SMZ), and sulphamethoxazole (SMR) were purchased from Aladdin Bio-Chem Technology Co., Ltd. Oleic acid (OA), oleylamine (OAm), N,N-dimethylformamide (DMF), anhydrous ethanol, n-hexane and dichloromethane were purchased from Tianjin Daimao Chemical Reagent Factory. Acrylamide (AM) and sulphadoxine-pyrimethamine (SD) were purchased from Nanjing Dulai Bio-technology Co., Ltd. Oxytetracycline was purchased from Shanghai Yuanye Biotechnology Co., Ltd. Toluene was purchased from Henan Haohua Chemical Reagent Co., Ltd. 2.2. Instruments The UV–visible absorption spectra were recorded on Evolution 220 UV–vis spectrophotometer (Thermofisher, America). Transmission electron microscopy (TEM) was performed with Tecnai G2 F20 TEM machine (FEI America). The fluorescence measurements were obtained by F97 XP fluorescence spectrometer (lengguang, China). Fourier transform infrared (FT-IR) spectra were recorded in the range of 500–4000 cm − 1 at Spectrum TWO FT-IR (Shimadzu, Japan). X-ray Photoelectron Spectroscopies (XPS) were recorded on Thermo SCIENTIFIC ESCALAB 250Xi XPS instrument. The X-ray diffraction (XRD) spectra were collected on XRD-6100 Lab X-ray diffractometer (Shimadzu, Japan). Fluorescence decay curves were measured with the FLS1000 transient steady state fluorescence spectrometer (Edinburgh, England). 2.3 Synthesis of Cs 3 Bi 2 Br 9 QDs Firstly, 0.3 mmol CsBr was added to a mixture of 2.8 mL DMF, 0.2 mL DMSO, and 1.0 mL PEG, and sonicated for 30min at 60°C to dissolve it completely. 0.2 mmol of BiBr 3 was added to 2.0 mL of EAC and sonicated for 10min to dissolve it. The above two solutions were mixed and 50 µL of OAm was added to form a light-yellow precursor solution. Then 5.5mL OA was added to 5.0mL anhydrous ethanol, and 0.75mL precursor solution was added to the above mixed solution. After stirring for 1min, the solution was centrifuged at 10000 rpm for 5min, the precipitate was discarded, and the supernatant was the Cs 3 Bi 2 Br 9 PQDs solution. 2.4 Fluorescence detection In the detection process, all the instrument conditions of fluorescence measurement were unified conditions, the slit width of excitation and emission were fixed at 10 nm, the excitation wavelength was 320 nm, the recorded emission wavelength was 340 ~ 430 nm, and the photomultiplier voltage was 750 V. The standard solution of OTC (1.0 mmol L − 1 ) was prepared and stored at 4°C. 63 µL of Cs 3 Bi 2 Br 9 PQDs solution was added to a 10 mL standard colorimetric tube with different amounts of OTC standard solution. The volume was made up to 10 mL with anhydrous ethanol and mixed evenly. After 1min, a portion of the solution was transferred to a fluorescence cuvette to measure its fluorescence value. 2.5 Application in actual samples The Weihe River bank soil was selected as the actual sample. After drying and screening, 1.0 g of soil was added to 10 mL of ethanol and sonicated for 30min, and the supernatant was retained after centrifugation. The centrifuged soil sediment was again sonicated and dispersed in 10 mL of ethanol, the supernatant was retained after centrifugation, and the supernatant from both times was mixed and set aside as soil sample solution. 3. Results and discussion 3.1 Preparation of Cs 3 Bi 2 Br 9 PQDs In this study, a green synthesis method was designed to prepare Cs 3 Bi 2 Br 9 PQDs. In terms of solvents, DMF, DMSO and EAC were selected as low toxicity and high solubility solvents, which could dissolve most of the precursors in perovskite system. Ethanol was selected as low solubility solvent due to its low toxicity, high miscibility and cost-effectiveness. In addition, the environmentally friendly non-toxic Bi element instead of Pb element made the synthesis process more green and environmental protection, and effectively avoided secondary pollution to the environment. The synthesis process of Cs 3 Bi 2 Br 9 PQDs is shown in Fig. 1 , CsBr was first dissolved in a mixture of DMF and DMSO, and BiBr 3 was dissolved in EAC, after which the two solutions were mixed and added to OAm for stirring. Finally, the precursor solution was added to the rapidly agitated low solubility solvent ethanol containing OA, and the Cs 3 Bi 2 Br 9 crystallized out. With the presence of OAm and OA, Cs 3 Bi 2 Br 9 PQDs were stably dispersed in ethanol solvent, and the surface defects of Cs 3 Bi 2 Br 9 were filled to make them have sufficient stability and optical properties. In order to optimize the experimental conditions, the effects of different reaction temperatures, OA dosages, OAm dosages and centrifugal reaction times on the optical properties of Cs 3 Bi 2 Br 9 PQDs were examined. The results are shown in Fig. 2 . As the temperature increased from room temperature (RT = 25°C) to 80°C, the fluorescence intensities of the quantum dots had slight ups and downs, but they were all generally maintained at a relatively equilibrium level, indicating that the reaction temperature did not have much effect on the fluorescence intensity of the PQDs. From the fluorescence intensity change trend of Cs 3 Bi 2 Br 9 PQDs, it can be seen that the fluorescence intensity decreased slightly with the continuous increase of OA dosage, and then increased continuously and finally leveled off. Next, the effect of OAm dosage on the fluorescence properties of Cs 3 Bi 2 Br 9 PQDs was investigated, and the fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs reached the maximum when the OAm dosage was 50 µL, and then had a large degree of decrease. Finally, the fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs had a slight decrease with the increase of centrifugation time. Therefore, in order to ensure the fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs, simplify the experimental conditions and ensure the adequacy of the reaction, 5 min was selected as the centrifugal reaction time, 25℃ was selected as the reaction temperature of the preparation process, 50 µL of OAm addition was selected as the amount of OAm required for the preparation process, and 5.5 mL of OA addition was selected as the amount of OA required for the preparation process. 3.2 Characterization of Cs 3 Bi 2 Br 9 PQDs The spectroscopic properties of the Cs 3 Bi 2 Br 9 PQDs were studied. Different excitation wavelengths will have a large impact on the emission spectra of quantum dots, which will affect the sensitive detection of OTC by the sensor. Figure 3 shows the emission spectra of Cs 3 Bi 2 Br 9 PQDs at different excitation wavelengths. When the excitation wavelength was 290 ~ 320 nm, the emission peak of Cs 3 Bi 2 Br 9 PQDs gradually redshifts with the increase of excitation wavelength, and the fluorescence intensity was gradually enhanced and reached the maximum value at 320 nm, when the wavelength was larger than 320 nm, its fluorescence intensity gradually decreased with the increase of the excitation wavelength. Therefore, 320 nm was selected as the optimal excitation wavelength for the subsequent detection experiments. We analyzed the microscopic morphology and size of the Cs 3 Bi 2 Br 9 PQDs by TEM, as shown in Fig. 4 (a), and the Cs 3 Bi 2 Br 9 PQDs were uniformly distributed in a spherical shape, with a particle size of about 5.0 nm. The lattice spacing of the Cs 3 Bi 2 Br 9 PQDs is shown in the inset of Fig. 4 (a) to be 0.338 nm, which corresponds to the Cs 3 Bi 2 Br 9 (200) crystalline facet. The results of the analysis of the XRD (Fig. 4 (b)) had also proved the presence of the crystalline facet. Subsequently, the functional group structure of Cs 3 Bi 2 Br 9 PQDs was analyzed by FT-IR to prove the successful synthesis of PQDs, as shown in Fig. 5 . The results show that the absorption peak at 3328.75 cm − 1 was attributed to the tensile vibration of N-H, the absorption peak at 2924.40 cm − 1 and 2855.13 cm − 1 originated from the vibrations of the C-H, and the absorption peak at 1709.51 cm − 1 represented the vibration of C = O. The peak position at 1668.64 cm − 1 was attributed to the vibration of C = C, the absorption peak at 1247.29 cm − 1 was attributed to the vibration of C-C, the absorption peak at 1046.40 cm − 1 represented the vibration of C-N, and the absorption peak at 664.10 cm − 1 was attributed to the vibration of O-H. The peaks at the above locations all proved the existence of OA and OAm, which greatly improved the stability and fluorescence properties of Cs 3 Bi 2 Br 9 PQDs. In addition, the elemental composition of Cs 3 Bi 2 Br 9 PQDs was further analyzed by XPS. As shown in Fig. 6 , Cs, Bi, Br, N elements can be detected. 3.3 Stability of Cs 3 Bi 2 Br 9 PQDs Since the dispersion and stability of quantum dots are affected by the nature of the solvent, the fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs dispersed in different solvents were examined (Fig. 7 (a)). At the excitation wavelength of 320 nm, it can be found that the emission peaks and fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs have large changes with the change of solvents. Cs 3 Bi 2 Br 9 PQDs had highest fluorescence intensities in toluene, comparatively high fluorescence intensities in dichloromethane and ethanol, a little weaker in n-hexane, and the weakest in aqueous solution. In addition, the stability of Cs 3 Bi 2 Br 9 PQDs in five solvents, namely, ethanol, dichloromethane, toluene, hexane and water, was further investigated in this experiment. The results, as shown in Fig. 7 (b), show that the fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs can remain stable in ethanol within 60 min. PQDs have a certain fluorescence intensity in the weakly polar toluene, dichloromethane and the non-polar solvent hexane, and even remain stable in highly polar aqueous solutions after a certain time. Thereby, considering the stability of Cs 3 Bi 2 Br 9 PQDs in solution, the solubility of OTC in solution and the toxicity of the solvent, ethanol was chosen as the detection solvent for the subsequent experiments. 3.4 Optimization of detection conditions for Cs 3 Bi 2 Br 9 PQDs The selection of the sensor solution concentration is a critical step in the detection of OTC, as it significantly impacts the sensitivity and linear range of the sensor. The optimal detection concentration was determined by studying the relative relationship between the fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs and the relative quenching quantity of 5.0 µM OTC across different concentration ranges (Fig. 8). When the concentration of Cs 3 Bi 2 Br 9 PQDs is low, exhibited high sensitivity but a narrower linear range due to easy fluorescence quenching by trace amounts of OTC. Conversely, at higher concentrations of Cs 3 Bi 2 Br 9 PQDs, there was an increase in fluorescence intensity but a relatively smaller quenching amount. To achieve higher sensitivity and wider linear range while considering both variables, a concentration of 7.0 µM was selected as optimal for Cs 3 Bi 2 Br 9 PQDs fluorescence sensor in OTC detection. Fig .8. Effect of Cs 3 Bi 2 Br 9 PQDs concentration on detection system. Based on the above studies, we explored the response time of Cs 3 Bi 2 Br 9 PQDs fluorescence sensor. As shown in Fig. 9 , the fluorescence intensity of the detection solution decreased rapidly in the initial 15s, followed by some up and down fluctuations in 1min, and then remained basically unchanged after that. The results show that the Cs 3 Bi 2 Br 9 PQDs fluorescent sensor had a fast response to OTC, Thus, 1 min was chosen as the best response time. The pH value has a certain effect on the fluorescence intensity and detection effect of fluorescent materials, and the effect of different pH values on the fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs is shown in Fig. 10 . The fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs gradually increased when pH was from 3.0 to 6.0, reaching the maximum value at pH = 6.0 before decreasing with further increases in pH. These results indicated that acidic and alkaline environments greatly affect the optical properties of sensor materials, with optimal fluorescence and detection performance observed only under weakly acidic or neutral conditions. Therefore, to simplify the experiment while maintaining reliable detection performance for Cs 3 Bi 2 Br 9 PQDs, pH = 7.0 was chosen as the optimal detection pH. 3.5 Quantitative detection of OTC by Cs 3 Bi 2 Br 9 PQDs On the basis of the above exploration, OTC was detected by adding different volumes of OTC standard solution into the sensor solution and recording corresponding fluorescence data, as shown in Fig. 11 , the fluorescence intensities of the sensor gradually reduced with the increase of OTC concentration, and this change rule is in accordance with the Stern-Volmer equation. See Formula.1, in which Ksv is the equation constant, and [C] is the concentration of OTC. F 0 and F represent the fluorescence intensity of the fluorescent sensor without OTC and with OTC. As shown in Fig. 11 (a), the linear fitting equation was F 0 /F = 0.03516C OTC + 0.97143, and fitting linear range was 2.0 ~ 18 µM with a correlation coefficient of R 2 of 0.9992. The detection limit (3σ/k) was 0.432 µM, where k is the slope of the fitted linear equation and σ is the standard deviation of the blank sample measurement (n = 10). $$\:\raisebox{1ex}{${F}_{0}$}\!\left/\:\!\raisebox{-1ex}{$F$}\right.=1+{K}_{SV}\left[C\right]$$ 1 3.6 Selectivity and anti-interference ability of Cs 3 Bi 2 Br 9 PQDs In order to further explore the selectivity and anti-interference capability of the Cs 3 Bi 2 Br 9 PQDs sensor, several common antibiotics and contaminants (SD, AM, 2,4,6-TCP, OPD, SMZ, SMR) were chosen as interfering substances. As can be seen from Fig. 12(a), the (F 0 -F)/F 0 was higher after adding OTC to Cs 3 Bi 2 Br 9 PQDs, while the (F 0 -F)/F 0 was at a lower level with the addition of other antibiotics or pollutants. After that, the interfering substances were mixed with OTC for the anti-interference experiment, as shown in Fig. 12(b). Compared with the blank group in which only OTC was added, the change in (F 0 -F)/F 0 after adding both interfering substances and OTC to the sensor was very small, indicating that the detection performance of the sensor was not interfered by other substances. Therefore, it was experimentally demonstrated that the Cs 3 Bi 2 Br 9 PQDs had good selectivity and strong anti-interference ability for OTC detection. Fig .12. (a) Selective research of Cs 3 Bi 2 Br 9 PQDs for OTC (5.0 µM) over other interference substances (30 µM) ;(b) Anti-interference study of Cs 3 Bi 2 Br 9 PQDs for OTC (5.0 µM) over other interference substances (30 µM). 3.7 Fluorescence detection mechanism Fluorescence quenching may be caused by a variety of mechanisms including static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer (PET) and inner filter effect (IFE) [31–33] . To elucidate the feasibility mechanism of OTC quenching Cs 3 Bi 2 Br 9 PQDs fluorescence, according to the main characteristics of various fluorescence quenching mechanisms, a systematic analysis method was adopted to exclude and verify them. (1) Verify whether the emission spectrum or excitation spectrum of the quantum dot overlaps with the absorption spectrum of the target object: As shown in Fig. 13 , the ultraviolet absorption spectrum of OTC strongly overlaps with the excitation and emission spectrum of Cs 3 Bi 2 Br 9 PQDs, so the possible mechanism of fluorescence quenching in this experiment includes FRET or IFE. (2) Verification of IFE mechanism proportion: In order to further clarify the mechanism, the corresponding fluorescence intensity of Cs 3 Bi 2 Br 9 PQDs in the presence of different concentrations of OTC was corrected according to Formula.2. $$\:{F}_{corr}={F}_{obs}\times\:antilog\left(\frac{{A}_{ex}+{A}_{em}}{2}\right)$$ 2 F obs is the observed fluorescence intensity, F corr is the corrected fluorescence intensity after subtracting the IFE mechanism quenched fluorescence value from F obs . A ex and A em are the absorbance of OTC at the excitation and emission wavelengths of Cs 3 Bi 2 Br 9 PQDs, respectively, as shown in Table 1 below. Table 1 The absorbance of OTC at the excitation and emission wavelengths of Cs 3 Bi 2 Br 9 PQDs OTC concentration (µM) 0 2 4 8 12 15 18 A ex : Excitation wavelength (320 nm) 0.069 0.098 0.124 0.175 0.225 0.265 0.298 A em : Emission wavelength (365 nm) 0.056 0.078 0.097 0.138 0.175 0.206 0.23 The suppressed efficiency of corrected fluorescence and observed fluorescence was calculated according to Formula.3. $$\:E=\left(1-\frac{F}{{F}_{0}}\right)\times\:100\%$$ 3 Based on the relationship between the suppressed efficiency of observed and corrected fluorescence and the concentration of OTC (Fig. 13 (b)). it is inferred that IFE is the mechanism of OTC quenching Cs 3 Bi 2 Br 9 PQDs fluorescence, and the possibility of FRET is ruled out. (3) Verify whether the fluorescence lifetime of Cs 3 Bi 2 Br 9 PQDs changes before and after the addition of OTC: The fluorescence lifetime of quantum dots is measured using a transient fluorescence spectrometer, the fluorescence lifetime decay curve is fitted, and the detection mechanism is further analyzed. One of the characteristics of the IFE detection mechanism is that the fluorescence lifetime of the sensor does not change before and after the addition of the target, but other mechanisms do not have this feature. As shown in Fig. 14 below, the fluorescence lifetime of Cs 3 Bi 2 Br 9 PQDs hardly changed with the addition of oxytetracycline. The fluorescence lifetime curve can be fitted by Formula.4 exponential decay curve: $$\:I\left(t\right)={I}_{0}+{A}_{1}{exp}\left(\frac{-t}{{\tau\:}_{1}}\right)+{A}_{2}{exp}\left(\frac{-t}{{\tau\:}_{2}}\right)$$ 4 The average fluorescence lifetime is fitted by A double exponential fitting model in Formula.5, where A is the amplitude and τ is the fluorescence lifetime: $$\:{\tau\:}_{ave}=\frac{（{A}_{1}{\tau\:}_{1}^{2}+{A}_{2}{\tau\:}_{2}^{2}）}{（{A}_{1}{\tau\:}_{1}+{A}_{2}{\tau\:}_{2}）}$$ 5 The transient fluorescence lifetime parameters obtained by fitting are shown in Table 2 , in which R 2 represents the fitting relevance, and the closer it is to 1, the more reliable the fitting equation is. In the absence of OTC, the average fluorescence lifetime of Cs 3 Bi 2 Br 9 PQDs is 2.74 ns, and in the presence of OTC, the average fluorescence lifetime is 2.62 ns, and the fluorescence lifetime is almost unchanged, indicating that the detection mechanism of the fluorescence sensor is IFE process. Table 2 Fitting parameters of the PL decay curves. I 0 τ 1 (ns) τ 2 (ns) A 1 A 2 τ ave (ns) R 2 Cs 3 Bi 2 Br 9 PQDs 0.035 1.31 5.95 5.80 0.567 2.74 0.999 Cs 3 Bi 2 Br 9 PQDs with OTC 0.032 1.29 5.78 6.12 0.576 2.62 0.999 before and after OTC was added. 3.8 Application to soil sample analysis Using Weihe River bank soil samples to analyze the detection ability of Cs 3 Bi 2 Br 9 PQDs in real samples. Since OTC was not detected in the samples, fluorescence detection was performed by labeling recovery experiment. Various concentrations of OTC standard solution were added to the sample, and the resulting measured to calculate the concentration of OTC using the fitting curve. As shown in Table 3 , the recoveries of OTC by the sensor ranged from 94.5–101.61%, with the relative standard deviations ranged from 3.9–6.5%, respectively. The above results indicate that the Cs 3 Bi 2 Br 9 PQDs sensor has potential for application in detecting OTC in real environmental samples. Table 3 Recovery of OTC in the spiked soil samples at different concentrations (n = 5) sample Concentration taken (µM) Found (µM) Recovery (%) RSD (%) 1 2.0 1.895 94.78 5.7 2 4.0 3.828 95.7 4.1 3 8.0 7.56 94.5 5.5 4 12 11.89 99.1 3.9 5 18 18.29 101.61 6.5 4. Conclusions In summary, we have presented the synthesis of Cs 3 Bi 2 Br 9 QDs with excellent stability and photoluminescence by replacing lead with green element bismuth, which effectively avoids environmental toxicity caused by lead while offering a simple operation method with low toxicity suitable for large-scale preparation. A new environmentally friendly detection system of OTC in ethanol was established by using bismuth-based perovskite quantum dots as fluorescent probe, enabling highly sensitive fluorescence quantitative detection of OTC. The sensor had high selectivity and sensitivity of OTC in ethanol, and the detection limit was 0.432 µM. Furthermore, successful application of this sensor for trace-level detection of OTC in real samples expands the utilization scope of bismuth perovskite quantum dots for environmental trace pollutants analysis. Declarations Author Statement Jiali Liu, Chen Li and Shen Zhang: conceived the idea and conducted the Data curation, Formal analysis, and Writing-original draft. Xiao Wei: Methodology, Supervision, Project administration, and Writing-review & editing. Xinni Liu, Yue Gao, Fei Wang, Mengwei Yan, Jiaqi Wang and Diana Kamuti: assisted during data analysis and some experiments. Conflicts of Interest or Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability The datasets used or analyzed during the current study are available from the corresponding author on reasonable request. Acknowledgments This work was supported by the National Natural Science Foundation of China (grant number 42207101); and the Fundamental Research Funds for the Central Universities, CHD (grant number 300102293208) Ethics Approval Declaration There was no ethics approval. References I. Moro, R. Trentin, E. Moschin, F.D. Vecchia, Morpho-physiological responses by Isochrysis galbana Parke to different concentrations of oxytetracycline, Environmental Pollution, 262 (2020) 114273.http://doi.org/10.1016/j.envpol.2020.114273. Q.L. Hu, L.S. Wang, N.N. Yu, Z.F. Zhang, X. Zheng, X.M. 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Chen, Lead-Free Cs 3 Bi 2 Br 9 Perovskite Quantum Dots for Detection of Heavy Metal Cu 2+ Ions in Seawater, Journal of Marine Science and Engineering, 11 (2023).http://doi.org/10.3390/jmse11051001. Z. Zhang, L. Liu, H. Huang, L. Li, J. Xu, Encapsulation of CsPbBr 3 perovskite quantum dots into PPy conducting polymer: Exceptional water stability and enhanced charge transport property, Applied Surface Science, 526 (2020) 146735.http://doi.org/10.1016/j.apsusc.2020.146735. D. Li, W. Xu, D. Zhou, X. Ma, X. Chen, G. Pan, J. Zhu, Y. Ji, N. Ding, H. Song, Cesium tin halide perovskite quantum dots as an organic photoluminescence probe for lead ion, Journal of Luminescence, 216 (2019).http://doi.org/10.1016/j.jlumin.2019.116711. R.D. Nelson, K. Santra, Y. Wang, A. Hadi, J. Petrich, M. Panthani, Synthesis and Optical Properties of Ordered-Vacancy Perovskite Cesium Bismuth Halide Nanocrystals, Chemical Communications, 54 (2018) 3640-3643.http://doi.org/10.1039/c7cc07223f. M.J. Molaei, Principles, mechanisms, and application of carbon quantum dots in sensors: a review, Analytical Methods, 12 (2020) 1266-1287.http://doi.org/10.1039/c9ay02696g. F. Zu, F. Yan, Z. Bai, J. Xu, Y. Wang, Y. Huang, X. Zhou, The quenching of the fluorescence of carbon dots: A review on mechanisms and applications, Microchimica Acta, 184 (2017) 1899-1914.http://doi.org/10.1007/s00604-017-2318-9. Z. Liang, M. Kang, G.F. Payne, X. Wang, R.C. Sun, Probing Energy and Electron Transfer Mechanisms in Fluorescence Quenching of Biomass Carbon Quantum Dots, ACS Applied Materials and Interfaces, 8 (2016) 17478-17488.http://doi.org/10.1021/acsami.6b04826. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 24 Sep, 2024 Reviews received at journal 22 Sep, 2024 Reviews received at journal 13 Sep, 2024 Reviewers agreed at journal 01 Sep, 2024 Reviewers agreed at journal 19 Aug, 2024 Reviewers invited by journal 16 Aug, 2024 Editor assigned by journal 16 Aug, 2024 Submission checks completed at journal 16 Aug, 2024 First submitted to journal 15 Aug, 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. 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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-4918535","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":350875861,"identity":"90dc1ee1-96e6-4b56-a16f-48972d0a0143","order_by":0,"name":"Jiali Liu","email":"","orcid":"","institution":"Chang’an University","correspondingAuthor":false,"prefix":"","firstName":"Jiali","middleName":"","lastName":"Liu","suffix":""},{"id":350875862,"identity":"65ce9fed-48b3-4d75-8324-2cb18a8849d3","order_by":1,"name":"Chen Li","email":"","orcid":"","institution":"Chang’an 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system.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/c7fe753b763c8c35e630d5b8.png"},{"id":64379874,"identity":"d86c4a8a-8eb0-4bf2-ac1c-5dd35573316c","added_by":"auto","created_at":"2024-09-12 11:18:58","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":39953,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eResponse time of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9 \u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePQDs for detecting OTC.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/efdb89140997f9191380470a.png"},{"id":64379142,"identity":"f2967160-92d7-48bc-9be9-acc7631d2f16","added_by":"auto","created_at":"2024-09-12 11:10:58","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":36714,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFluorescence intensities of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9 \u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePQDs solution at different pH conditions.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/e26da36de19921032af00f36.png"},{"id":64380758,"identity":"529787d7-4aad-41fb-96d5-d3b53808351c","added_by":"auto","created_at":"2024-09-12 11:34:58","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":132741,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLinear fitting curve (a) and fluorescence quenching degree (b) of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e PQDs for different concentrations of OTC.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/f21429c6fbc474002d617831.png"},{"id":64379144,"identity":"f2262851-987a-4e08-92ec-531a664a3f08","added_by":"auto","created_at":"2024-09-12 11:10:58","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":207711,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e \u003cstrong\u003eSelective research of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e PQDs for OTC (5.0 μM) over other interference substances (30 μM) ;(b)\u003c/strong\u003e \u003cstrong\u003eAnti-interference study of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e PQDs for OTC (5.0 μM) over other interference substances (30 μM).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/c6745b3c3b2ad84a05051799.png"},{"id":64379147,"identity":"6f53317b-0cb0-49a2-a012-1bc0c5a46f5c","added_by":"auto","created_at":"2024-09-12 11:10:58","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":109146,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) UV-absorption spectrum of OTC, the excitation and emission\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003efluorescence spectra of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e PQDs ;(b) Suppressed efficiency of observed and corrected fluorescence of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e PQDs after addition of different concentrations of OTC.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/94b2cb35745664d7599abcd0.png"},{"id":64379149,"identity":"9e2fa79f-df7c-4689-a70a-511f26121272","added_by":"auto","created_at":"2024-09-12 11:10:58","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":185151,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFluorescence lifetime attenuation curve of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e PQDs\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ebefore and after OTC was added.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/1b7d69c58cbc4e4bf5118609.png"},{"id":64381457,"identity":"cb1a395c-6223-4690-9afa-f5851e01cc93","added_by":"auto","created_at":"2024-09-12 11:43:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3316934,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4918535/v1/d7d83163-5ba2-4058-9db4-2413ab370b0e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Environment-friendly lead-free Cs3Bi2Br9 perovskite quantum dots as fluorescent probes for rapid detection of oxytetracycline via inner filter effect","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOxytetracycline (OTC), as an antimicrobial compound, is extensively utilized in medicine, animal husbandry and aquaculture due to its cost-effectiveness and broad spectrum\u003csup\u003e[1, 2]\u003c/sup\u003e. However, OTC is difficult to be adsorbed and degraded in the animal body, and most of it will enter into excreta (faeces, urine, etc.) and discharged wastes in the form of original and intermediate products, which causes serious pollution in the ecological environment\u003csup\u003e[3]\u003c/sup\u003e. In addition, excessive use of OTC can lead to high levels of residues in animal-derived food, posing a serious threat to human health by causing liver damage, bone disorders, gastrointestinal issues, and renal dysfunction\u003csup\u003e[4, 5]\u003c/sup\u003e. Studies have demonstrated that OTC has been detected in drinking water and food products (milk, meat and honey, etc.)\u003csup\u003e[6, 7]\u003c/sup\u003e. Therefore, it is crucial to monitor and detect residual OTC levels in animal-derived foods and aquatic environments for the sake of human health. Currently available methods for determining residual levels of OTC include high-performance liquid chromatography (HPLC)\u003csup\u003e[8]\u003c/sup\u003e, microbial\u003csup\u003e[9]\u003c/sup\u003e and electrochemical methods\u003csup\u003e[10]\u003c/sup\u003e. But these methods have the drawbacks including lengthy operation time, extensive pre-treatment steps, costliness and high reagent consumption\u003csup\u003e[11\u0026ndash;13]\u003c/sup\u003e. Hence, it is imminent to develop a method with easy-to-operate, rapid, and highly selective to detect residual OTC.\u003c/p\u003e \u003cp\u003eIn recent years, fluorescent sensors prepared with quantum dots (QDs) as fluorescent groups have achieved the advantages of simple operation, low cost, good sensitivity and selectivity, and good stability. So far, QDs have been used for the detection of various pollutants, such as tetracycline\u003csup\u003e[14]\u003c/sup\u003e, dopamine\u003csup\u003e[15]\u003c/sup\u003e, sulfonamides\u003csup\u003e[16]\u003c/sup\u003e, organophosphorus pesticides\u003csup\u003e[17]\u003c/sup\u003e, etc. However, traditional quantum dots (CdTe QDs, Si QDs, ZnS QDs, etc.) mostly have defects including expensive reagents and weak luminous intensity. These limitations prevent them from meeting the requirements of highly sensitive analysis detection. Since the first report of perovskite quantum dots (PQDs), they have received extensive attention from researchers for their high photoluminescence quantum yield (PLQY\u0026thinsp;\u0026gt;\u0026thinsp;90%), narrower full width at half-maximum (FWHM:12\u0026ndash;25 nm) and tunable emission wavelength. PQDs have great development potential in solar energy\u003csup\u003e[18]\u003c/sup\u003e, light-emitting diode\u003csup\u003e[19]\u003c/sup\u003e, laser\u003csup\u003e[20]\u003c/sup\u003e, fluorescence detection\u003csup\u003e[21]\u003c/sup\u003e and other fields. In recent years, fluorescent sensors constructed with PQDs as fluorescent groups have been used for the detection of heavy metal ions\u003csup\u003e[22]\u003c/sup\u003e, organics\u003csup\u003e[23]\u003c/sup\u003e, gases\u003csup\u003e[24]\u003c/sup\u003e and anions\u003csup\u003e[25]\u003c/sup\u003e. Nevertheless, most of these detections were performed in non-polar solvents, because the strong ionic nature of PQDs renders them extremely sensitive to the external environment\u003csup\u003e[26]\u003c/sup\u003e. Additionally, lead-based PQDs contain lead element which is one of the three major heavy metal pollutants, it accumulates through food chains due to its bioaccumulation ability and non-degradability thereby polluting the environment. When the lead content in human body reaches a certain level, it can cause fatigue, muscle weakness, clumsiness, and confusion\u003csup\u003e[27]\u003c/sup\u003e. Therefore, how to overcome the stability and toxicity problems has become a must for the green and sustainable development of PQDs.\u003c/p\u003e \u003cp\u003eAt present, in order to effectively reduce the impact of PQDs toxicity on the environment, it is an effective strategy to encapsulate Pb\u003csup\u003e2+\u003c/sup\u003e into a tightly structured polymer matrix to reduce the diffusion of Pb\u003csup\u003e2+\u003c/sup\u003e in the environment. Zhang et al.\u003csup\u003e[28]\u003c/sup\u003e synthesized a stable CsPbBr\u003csub\u003e3\u003c/sub\u003e/polypyrrole (PPy) composite by photocatalytic polymerization, and PQDs were encapsulated in the PPy protective layer to reduce the environmental impact of Pb\u003csup\u003e2+\u003c/sup\u003e toxicity to a certain extent. However, this method cannot essentially eliminate the environmental hazards of lead-based PQDs. In addition to this, it has been mentioned in the literature to prepare environmentally friendly perovskite quantum dots using non-toxic metals such as tin (Sn) instead of lead (Pb)\u003csup\u003e[29]\u003c/sup\u003e, CsSnX\u003csub\u003e3\u003c/sub\u003e prepared using divalent tin was highly susceptible to conditions such as light and temperature, which is due to the fact that Sn(II) can be oxidized very easily to Sn(IV). The PLQY of CsSnX\u003csub\u003e3\u003c/sub\u003e is much lower than Pb-based analogues\u003csup\u003e[30]\u003c/sup\u003e. Trivalent bismuth is harmless to human body and is a kind of \"green metal\" that shares many similar properties with lead, such as isoelectronic structure (6s\u003csup\u003e2\u003c/sup\u003e6p\u003csup\u003e0\u003c/sup\u003e) and similar ionic radius(Bi\u003csup\u003e3+\u003c/sup\u003e:1.03\u0026Aring;, Pb\u003csup\u003e2+\u003c/sup\u003e:1.19\u0026Aring;), and is more stable than tin. So bismuth is the best candidate material for preparing non-toxic perovskite materials.\u003c/p\u003e \u003cp\u003eHerein, environment-friendly lead-free Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs were synthesized as a fluorescent sensor by using ligand-assisted reprecipitation method with OA and OAm as ligands, which achieves high sensitivity detection of trace OTC in ethanol based on the inner filter effect. The synthesized Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs can not only be stably dispersed in the ethanol phase, but we used the green metal-bismuth element to replace the lead element, effectively avoiding the secondary pollution to the environment. In addition, the structure, properties, detection conditions and quenching mechanism of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs were characterized and studied in detail, and the obtained fluorescence sensor was successfully used for OTC detection of soil samples.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Chemicals and materials\u003c/h2\u003e \u003cp\u003eAll chemicals were analytical reagent grade and used as received without any further purification. Bismuth bromide (BiBr\u003csub\u003e3\u003c/sub\u003e), cesium bromide (CsBr), dimethyl sulfoxide (DMSO), polyethylene glycol 200 (PEG), ethyl acetate (EAC), 2,4,6-trichlorophenol (2,4,6-TCP), o-phenylenediamine (OPD), sulphamethoxazole (SMZ), and sulphamethoxazole (SMR) were purchased from Aladdin Bio-Chem Technology Co., Ltd. Oleic acid (OA), oleylamine (OAm), N,N-dimethylformamide (DMF), anhydrous ethanol, n-hexane and dichloromethane were purchased from Tianjin Daimao Chemical Reagent Factory. Acrylamide (AM) and sulphadoxine-pyrimethamine (SD) were purchased from Nanjing Dulai Bio-technology Co., Ltd. Oxytetracycline was purchased from Shanghai Yuanye Biotechnology Co., Ltd. Toluene was purchased from Henan Haohua Chemical Reagent Co., Ltd.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Instruments\u003c/h2\u003e \u003cp\u003eThe UV\u0026ndash;visible absorption spectra were recorded on Evolution 220 UV\u0026ndash;vis spectrophotometer (Thermofisher, America). Transmission electron microscopy (TEM) was performed with Tecnai G2 F20 TEM machine (FEI America). The fluorescence measurements were obtained by F97 XP fluorescence spectrometer (lengguang, China). Fourier transform infrared (FT-IR) spectra were recorded in the range of 500\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at Spectrum TWO FT-IR (Shimadzu, Japan). X-ray Photoelectron Spectroscopies (XPS) were recorded on Thermo SCIENTIFIC ESCALAB 250Xi XPS instrument. The X-ray diffraction (XRD) spectra were collected on XRD-6100 Lab X-ray diffractometer (Shimadzu, Japan). Fluorescence decay curves were measured with the FLS1000 transient steady state fluorescence spectrometer (Edinburgh, England).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Synthesis of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e QDs\u003c/h2\u003e \u003cp\u003eFirstly, 0.3 mmol CsBr was added to a mixture of 2.8 mL DMF, 0.2 mL DMSO, and 1.0 mL PEG, and sonicated for 30min at 60\u0026deg;C to dissolve it completely. 0.2 mmol of BiBr\u003csub\u003e3\u003c/sub\u003e was added to 2.0 mL of EAC and sonicated for 10min to dissolve it. The above two solutions were mixed and 50 \u0026micro;L of OAm was added to form a light-yellow precursor solution. Then 5.5mL OA was added to 5.0mL anhydrous ethanol, and 0.75mL precursor solution was added to the above mixed solution. After stirring for 1min, the solution was centrifuged at 10000 rpm for 5min, the precipitate was discarded, and the supernatant was the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs solution.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Fluorescence detection\u003c/h2\u003e \u003cp\u003eIn the detection process, all the instrument conditions of fluorescence measurement were unified conditions, the slit width of excitation and emission were fixed at 10 nm, the excitation wavelength was 320 nm, the recorded emission wavelength was 340\u0026thinsp;~\u0026thinsp;430 nm, and the photomultiplier voltage was 750 V. The standard solution of OTC (1.0 mmol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was prepared and stored at 4\u0026deg;C. 63 \u0026micro;L of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs solution was added to a 10 mL standard colorimetric tube with different amounts of OTC standard solution. The volume was made up to 10 mL with anhydrous ethanol and mixed evenly. After 1min, a portion of the solution was transferred to a fluorescence cuvette to measure its fluorescence value.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Application in actual samples\u003c/h2\u003e \u003cp\u003eThe Weihe River bank soil was selected as the actual sample. After drying and screening, 1.0 g of soil was added to 10 mL of ethanol and sonicated for 30min, and the supernatant was retained after centrifugation. The centrifuged soil sediment was again sonicated and dispersed in 10 mL of ethanol, the supernatant was retained after centrifugation, and the supernatant from both times was mixed and set aside as soil sample solution.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec9\"\u003e\n \u003ch2\u003e3.1 Preparation of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/h2\u003e\n \u003cp\u003eIn this study, a green synthesis method was designed to prepare Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs. In terms of solvents, DMF, DMSO and EAC were selected as low toxicity and high solubility solvents, which could dissolve most of the precursors in perovskite system. Ethanol was selected as low solubility solvent due to its low toxicity, high miscibility and cost-effectiveness. In addition, the environmentally friendly non-toxic Bi element instead of Pb element made the synthesis process more green and environmental protection, and effectively avoided secondary pollution to the environment. The synthesis process of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs is shown in Fig. \u003cspan\u003e1\u003c/span\u003e, CsBr was first dissolved in a mixture of DMF and DMSO, and BiBr\u003csub\u003e3\u003c/sub\u003e was dissolved in EAC, after which the two solutions were mixed and added to OAm for stirring. Finally, the precursor solution was added to the rapidly agitated low solubility solvent ethanol containing OA, and the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e crystallized out. With the presence of OAm and OA, Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs were stably dispersed in ethanol solvent, and the surface defects of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e were filled to make them have sufficient stability and optical properties.\u003c/p\u003e\n \u003cp\u003eIn order to optimize the experimental conditions, the effects of different reaction temperatures, OA dosages, OAm dosages and centrifugal reaction times on the optical properties of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs were examined. The results are shown in Fig. \u003cspan\u003e2\u003c/span\u003e. As the temperature increased from room temperature (RT\u0026thinsp;=\u0026thinsp;25\u0026deg;C) to 80\u0026deg;C, the fluorescence intensities of the quantum dots had slight ups and downs, but they were all generally maintained at a relatively equilibrium level, indicating that the reaction temperature did not have much effect on the fluorescence intensity of the PQDs. From the fluorescence intensity change trend of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs, it can be seen that the fluorescence intensity decreased slightly with the continuous increase of OA dosage, and then increased continuously and finally leveled off. Next, the effect of OAm dosage on the fluorescence properties of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs was investigated, and the fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs reached the maximum when the OAm dosage was 50 \u0026micro;L, and then had a large degree of decrease. Finally, the fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs had a slight decrease with the increase of centrifugation time. Therefore, in order to ensure the fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs, simplify the experimental conditions and ensure the adequacy of the reaction, 5 min was selected as the centrifugal reaction time, 25℃ was selected as the reaction temperature of the preparation process, 50 \u0026micro;L of OAm addition was selected as the amount of OAm required for the preparation process, and 5.5 mL of OA addition was selected as the amount of OA required for the preparation process.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\"\u003e\n \u003ch2\u003e3.2 Characterization of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/h2\u003e\n \u003cp\u003eThe spectroscopic properties of the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs were studied. Different excitation wavelengths will have a large impact on the emission spectra of quantum dots, which will affect the sensitive detection of OTC by the sensor. Figure \u003cspan\u003e3\u003c/span\u003e shows the emission spectra of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs at different excitation wavelengths. When the excitation wavelength was 290\u0026thinsp;~\u0026thinsp;320 nm, the emission peak of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs gradually redshifts with the increase of excitation wavelength, and the fluorescence intensity was gradually enhanced and reached the maximum value at 320 nm, when the wavelength was larger than 320 nm, its fluorescence intensity gradually decreased with the increase of the excitation wavelength. Therefore, 320 nm was selected as the optimal excitation wavelength for the subsequent detection experiments.\u003c/p\u003e\n \u003cp\u003eWe analyzed the microscopic morphology and size of the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs by TEM, as shown in Fig. \u003cspan\u003e4\u003c/span\u003e(a), and the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs were uniformly distributed in a spherical shape, with a particle size of about 5.0 nm. The lattice spacing of the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs is shown in the inset of Fig. \u003cspan\u003e4\u003c/span\u003e(a) to be 0.338 nm, which corresponds to the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e(200) crystalline facet. The results of the analysis of the XRD (Fig. \u003cspan\u003e4\u003c/span\u003e(b)) had also proved the presence of the crystalline facet.\u003c/p\u003e\n \u003cp\u003eSubsequently, the functional group structure of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs was analyzed by FT-IR to prove the successful synthesis of PQDs, as shown in Fig. \u003cspan\u003e5\u003c/span\u003e. The results show that the absorption peak at 3328.75 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to the tensile vibration of N-H, the absorption peak at 2924.40 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2855.13 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e originated from the vibrations of the C-H, and the absorption peak at 1709.51 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e represented the vibration of C\u0026thinsp;=\u0026thinsp;O. The peak position at 1668.64 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to the vibration of C\u0026thinsp;=\u0026thinsp;C, the absorption peak at 1247.29 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to the vibration of C-C, the absorption peak at 1046.40 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e represented the vibration of C-N, and the absorption peak at 664.10 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to the vibration of O-H. The peaks at the above locations all proved the existence of OA and OAm, which greatly improved the stability and fluorescence properties of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs. In addition, the elemental composition of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs was further analyzed by XPS. As shown in Fig. \u003cspan\u003e6\u003c/span\u003e, Cs, Bi, Br, N elements can be detected.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\"\u003e\n \u003ch2\u003e3.3 Stability of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/h2\u003e\n \u003cp\u003eSince the dispersion and stability of quantum dots are affected by the nature of the solvent, the fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs dispersed in different solvents were examined (Fig. \u003cspan\u003e7\u003c/span\u003e(a)). At the excitation wavelength of 320 nm, it can be found that the emission peaks and fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs have large changes with the change of solvents. Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs had highest fluorescence intensities in toluene, comparatively high fluorescence intensities in dichloromethane and ethanol, a little weaker in n-hexane, and the weakest in aqueous solution. In addition, the stability of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs in five solvents, namely, ethanol, dichloromethane, toluene, hexane and water, was further investigated in this experiment. The results, as shown in Fig. \u003cspan\u003e7\u003c/span\u003e(b), show that the fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs can remain stable in ethanol within 60 min. PQDs have a certain fluorescence intensity in the weakly polar toluene, dichloromethane and the non-polar solvent hexane, and even remain stable in highly polar aqueous solutions after a certain time. Thereby, considering the stability of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs in solution, the solubility of OTC in solution and the toxicity of the solvent, ethanol was chosen as the detection solvent for the subsequent experiments.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\"\u003e\n \u003ch2\u003e3.4 Optimization of detection conditions for Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/h2\u003e\n \u003cp\u003eThe selection of the sensor solution concentration is a critical step in the detection of OTC, as it significantly impacts the sensitivity and linear range of the sensor. The optimal detection concentration was determined by studying the relative relationship between the fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs and the relative quenching quantity of 5.0 \u0026micro;M OTC across different concentration ranges (Fig. 8). When the concentration of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs is low, exhibited high sensitivity but a narrower linear range due to easy fluorescence quenching by trace amounts of OTC. Conversely, at higher concentrations of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs, there was an increase in fluorescence intensity but a relatively smaller quenching amount. To achieve higher sensitivity and wider linear range while considering both variables, a concentration of 7.0 \u0026micro;M was selected as optimal for Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs fluorescence sensor in OTC detection.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFig .8. Effect of Cs\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e3\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003eBi\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e2\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003eBr\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e9\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003ePQDs concentration on detection system.\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eBased on the above studies, we explored the response time of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs fluorescence sensor. As shown in Fig. \u003cspan\u003e9\u003c/span\u003e, the fluorescence intensity of the detection solution decreased rapidly in the initial 15s, followed by some up and down fluctuations in 1min, and then remained basically unchanged after that. The results show that the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs fluorescent sensor had a fast response to OTC, Thus, 1 min was chosen as the best response time.\u003c/p\u003e\n \u003cp\u003eThe pH value has a certain effect on the fluorescence intensity and detection effect of fluorescent materials, and the effect of different pH values on the fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs is shown in Fig. \u003cspan\u003e10\u003c/span\u003e. The fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs gradually increased when pH was from 3.0 to 6.0, reaching the maximum value at pH\u0026thinsp;=\u0026thinsp;6.0 before decreasing with further increases in pH. These results indicated that acidic and alkaline environments greatly affect the optical properties of sensor materials, with optimal fluorescence and detection performance observed only under weakly acidic or neutral conditions. Therefore, to simplify the experiment while maintaining reliable detection performance for Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs, pH\u0026thinsp;=\u0026thinsp;7.0 was chosen as the optimal detection pH.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\"\u003e\n \u003ch2\u003e3.5 Quantitative detection of OTC by Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/h2\u003e\n \u003cp\u003eOn the basis of the above exploration, OTC was detected by adding different volumes of OTC standard solution into the sensor solution and recording corresponding fluorescence data, as shown in Fig. \u003cspan\u003e11\u003c/span\u003e, the fluorescence intensities of the sensor gradually reduced with the increase of OTC concentration, and this change rule is in accordance with the Stern-Volmer equation. See Formula.1, in which Ksv is the equation constant, and [C] is the concentration of OTC. F\u003csub\u003e0\u003c/sub\u003e and F represent the fluorescence intensity of the fluorescent sensor without OTC and with OTC. As shown in Fig. \u003cspan\u003e11\u003c/span\u003e(a), the linear fitting equation was F\u003csub\u003e0\u003c/sub\u003e/F\u0026thinsp;=\u0026thinsp;0.03516C\u003csub\u003eOTC\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;0.97143, and fitting linear range was 2.0\u0026thinsp;~\u0026thinsp;18 \u0026micro;M with a correlation coefficient of R\u003csup\u003e2\u003c/sup\u003e of 0.9992. The detection limit (3\u0026sigma;/k) was 0.432 \u0026micro;M, where k is the slope of the fitted linear equation and \u0026sigma; is the standard deviation of the blank sample measurement (n\u0026thinsp;=\u0026thinsp;10).\u003c/p\u003e\n \u003cdiv id=\"Equ1\"\u003e\n \u003cdiv id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$\\:\\raisebox{1ex}{${F}_{0}$}\\!\\left/\\:\\!\\raisebox{-1ex}{$F$}\\right.=1+{K}_{SV}\\left[C\\right]$$\u003c/div\u003e\n \u003cdiv\u003e1\u003c/div\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\"\u003e\n \u003ch2\u003e3.6 Selectivity and anti-interference ability of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/h2\u003e\n \u003cp\u003eIn order to further explore the selectivity and anti-interference capability of the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs sensor, several common antibiotics and contaminants (SD, AM, 2,4,6-TCP, OPD, SMZ, SMR) were chosen as interfering substances. As can be seen from Fig. 12(a), the (F\u003csub\u003e0\u003c/sub\u003e-F)/F\u003csub\u003e0\u003c/sub\u003e was higher after adding OTC to Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs, while the (F\u003csub\u003e0\u003c/sub\u003e-F)/F\u003csub\u003e0\u003c/sub\u003e was at a lower level with the addition of other antibiotics or pollutants. After that, the interfering substances were mixed with OTC for the anti-interference experiment, as shown in Fig. 12(b). Compared with the blank group in which only OTC was added, the change in (F\u003csub\u003e0\u003c/sub\u003e-F)/F\u003csub\u003e0\u003c/sub\u003e after adding both interfering substances and OTC to the sensor was very small, indicating that the detection performance of the sensor was not interfered by other substances. Therefore, it was experimentally demonstrated that the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs had good selectivity and strong anti-interference ability for OTC detection.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFig .12. (a) Selective research of Cs\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e3\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003eBi\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e2\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003eBr\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e9\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003ePQDs for OTC (5.0 \u0026micro;M) over other interference substances (30 \u0026micro;M) ;(b) Anti-interference study of Cs\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBi\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003ePQDs for OTC (5.0 \u0026micro;M) over other interference substances (30 \u0026micro;M).\u003c/strong\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\"\u003e\n \u003ch2\u003e3.7 Fluorescence detection mechanism\u003c/h2\u003e\n \u003cp\u003eFluorescence quenching may be caused by a variety of mechanisms including static quenching, dynamic quenching, F\u0026ouml;rster resonance energy transfer (FRET), photoinduced electron transfer (PET) and inner filter effect (IFE)\u003csup\u003e[31\u0026ndash;33]\u003c/sup\u003e. To elucidate the feasibility mechanism of OTC quenching Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs fluorescence, according to the main characteristics of various fluorescence quenching mechanisms, a systematic analysis method was adopted to exclude and verify them.\u003c/p\u003e\n \u003cp\u003e(1) Verify whether the emission spectrum or excitation spectrum of the quantum dot overlaps with the absorption spectrum of the target object: As shown in Fig. \u003cspan\u003e13\u003c/span\u003e, the ultraviolet absorption spectrum of OTC strongly overlaps with the excitation and emission spectrum of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs, so the possible mechanism of fluorescence quenching in this experiment includes FRET or IFE.\u003c/p\u003e\n \u003cp\u003e(2) Verification of IFE mechanism proportion: In order to further clarify the mechanism, the corresponding fluorescence intensity of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs in the presence of different concentrations of OTC was corrected according to Formula.2.\u003c/p\u003e\n \u003cdiv id=\"Equ2\"\u003e\n \u003cdiv id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$$\\:{F}_{corr}={F}_{obs}\\times\\:antilog\\left(\\frac{{A}_{ex}+{A}_{em}}{2}\\right)$$\u003c/div\u003e\n \u003cdiv\u003e2\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eF\u003csub\u003eobs\u003c/sub\u003e is the observed fluorescence intensity, F\u003csub\u003ecorr\u003c/sub\u003e is the corrected fluorescence intensity after subtracting the IFE mechanism quenched fluorescence value from F\u003csub\u003eobs\u003c/sub\u003e. A\u003csub\u003eex\u003c/sub\u003e and A\u003csub\u003eem\u003c/sub\u003e are the absorbance of OTC at the excitation and emission wavelengths of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs, respectively, as shown in Table \u003cspan\u003e1\u003c/span\u003e below. \u0026nbsp;\u003c/p\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eThe absorbance of OTC at the excitation and emission wavelengths of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOTC concentration (\u0026micro;M)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003eex\u003c/sub\u003e: Excitation wavelength (320 nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.069\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.098\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.124\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.175\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.225\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.265\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.298\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003eem\u003c/sub\u003e: Emission wavelength (365 nm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.056\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.078\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.097\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.175\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.206\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eThe suppressed efficiency of corrected fluorescence and observed fluorescence was calculated according to Formula.3.\u003c/p\u003e\n \u003cdiv id=\"Equ3\"\u003e\n \u003cdiv id=\"FileID_Equ3\" name=\"EquationSource\"\u003e$$\\:E=\\left(1-\\frac{F}{{F}_{0}}\\right)\\times\\:100\\%$$\u003c/div\u003e\n \u003cdiv\u003e3\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eBased on the relationship between the suppressed efficiency of observed and corrected fluorescence and the concentration of OTC (Fig. \u003cspan\u003e13\u003c/span\u003e(b)). it is inferred that IFE is the mechanism of OTC quenching Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs fluorescence, and the possibility of FRET is ruled out.\u003c/p\u003e\n \u003cp\u003e(3) Verify whether the fluorescence lifetime of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs changes before and after the addition of OTC: The fluorescence lifetime of quantum dots is measured using a transient fluorescence spectrometer, the fluorescence lifetime decay curve is fitted, and the detection mechanism is further analyzed. One of the characteristics of the IFE detection mechanism is that the fluorescence lifetime of the sensor does not change before and after the addition of the target, but other mechanisms do not have this feature. As shown in Fig. \u003cspan\u003e14\u003c/span\u003e below, the fluorescence lifetime of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs hardly changed with the addition of oxytetracycline. The fluorescence lifetime curve can be fitted by Formula.4 exponential decay curve:\u003c/p\u003e\n \u003cdiv id=\"Equ4\"\u003e\n \u003cdiv id=\"FileID_Equ4\" name=\"EquationSource\"\u003e$$\\:I\\left(t\\right)={I}_{0}+{A}_{1}{exp}\\left(\\frac{-t}{{\\tau\\:}_{1}}\\right)+{A}_{2}{exp}\\left(\\frac{-t}{{\\tau\\:}_{2}}\\right)$$\u003c/div\u003e\n \u003cdiv\u003e4\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eThe average fluorescence lifetime is fitted by A double exponential fitting model in Formula.5, where A is the amplitude and \u0026tau; is the fluorescence lifetime:\u003c/p\u003e\n \u003cdiv id=\"Equ5\"\u003e\n \u003cdiv id=\"FileID_Equ5\" name=\"EquationSource\"\u003e$$\\:{\\tau\\:}_{ave}=\\frac{（{A}_{1}{\\tau\\:}_{1}^{2}+{A}_{2}{\\tau\\:}_{2}^{2}）}{（{A}_{1}{\\tau\\:}_{1}+{A}_{2}{\\tau\\:}_{2}）}$$\u003c/div\u003e\n \u003cdiv\u003e5\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eThe transient fluorescence lifetime parameters obtained by fitting are shown in Table \u003cspan\u003e2\u003c/span\u003e, in which R\u003csup\u003e2\u003c/sup\u003e represents the fitting relevance, and the closer it is to 1, the more reliable the fitting equation is. In the absence of OTC, the average fluorescence lifetime of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs is 2.74 ns, and in the presence of OTC, the average fluorescence lifetime is 2.62 ns, and the fluorescence lifetime is almost unchanged, indicating that the detection mechanism of the fluorescence sensor is IFE process. \u0026nbsp;\u003c/p\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eFitting parameters of the PL decay curves.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eI\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026tau;\u003csub\u003e1\u003c/sub\u003e (ns)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026tau;\u003csub\u003e2\u003c/sub\u003e (ns)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eA\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026tau;\u003csub\u003eave\u003c/sub\u003e (ns)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.035\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e5.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.567\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs with OTC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.032\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e5.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.576\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.999\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ebefore and after OTC was added.\u003c/strong\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\"\u003e\n \u003ch2\u003e3.8 Application to soil sample analysis\u003c/h2\u003e\n \u003cp\u003eUsing Weihe River bank soil samples to analyze the detection ability of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs in real samples. Since OTC was not detected in the samples, fluorescence detection was performed by labeling recovery experiment. Various concentrations of OTC standard solution were added to the sample, and the resulting measured to calculate the concentration of OTC using the fitting curve. As shown in Table \u003cspan\u003e3\u003c/span\u003e, the recoveries of OTC by the sensor ranged from 94.5\u0026ndash;101.61%, with the relative standard deviations ranged from 3.9\u0026ndash;6.5%, respectively. The above results indicate that the Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs sensor has potential for application in detecting OTC in real environmental samples.\u0026nbsp;\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eRecovery of OTC in the spiked soil samples at different concentrations (n\u0026thinsp;=\u0026thinsp;5)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003esample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eConcentration taken (\u0026micro;M)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFound (\u0026micro;M)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRecovery (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRSD (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.895\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e94.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.828\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e95.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e94.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e99.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e101.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn summary, we have presented the synthesis of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e QDs with excellent stability and photoluminescence by replacing lead with green element bismuth, which effectively avoids environmental toxicity caused by lead while offering a simple operation method with low toxicity suitable for large-scale preparation. A new environmentally friendly detection system of OTC in ethanol was established by using bismuth-based perovskite quantum dots as fluorescent probe, enabling highly sensitive fluorescence quantitative detection of OTC. The sensor had high selectivity and sensitivity of OTC in ethanol, and the detection limit was 0.432 \u0026micro;M. Furthermore, successful application of this sensor for trace-level detection of OTC in real samples expands the utilization scope of bismuth perovskite quantum dots for environmental trace pollutants analysis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJiali Liu, Chen Li and Shen Zhang: conceived the idea and conducted the Data curation, Formal analysis, and Writing-original draft. Xiao Wei: Methodology, Supervision, Project administration, and Writing-review \u0026amp; editing. Xinni Liu, Yue Gao, Fei Wang, Mengwei Yan, Jiaqi Wang and Diana Kamuti: assisted during data analysis and some experiments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest or Competing Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (grant number 42207101); and the Fundamental Research Funds for the Central Universities, CHD (grant number 300102293208)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Approval Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere was no ethics approval.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eI. 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Sun, Probing Energy and Electron Transfer Mechanisms in Fluorescence Quenching of Biomass Carbon Quantum Dots, ACS Applied Materials and Interfaces, 8 (2016) 17478-17488.http://doi.org/10.1021/acsami.6b04826.\u003c/li\u003e\n\u003c/ol\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-cluster-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Journal of Cluster Science](https://www.springer.com/journal/10876) ","snPcode":"10876","submissionUrl":"https://mc.manuscriptcentral.com/jocl","title":"Journal of Cluster Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"bismuth perovskite quantum dots, oxytetracycline, fluorescence detection, inner filter effect","lastPublishedDoi":"10.21203/rs.3.rs-4918535/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4918535/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAll-inorganic perovskite quantum dots have sparked a research boom due to their excellent optical properties, however, their own strong ionicity and lead toxicity have hindered further development in the field of sensing. In this study, we have solved the toxicity problem of lead-based perovskite quantum dots by replacing lead with green metal bismuth. Meanwhile, due to the ligand-passivation effect of oleylamine and oleic acid, we successfully synthesized highly stable bismuth-based perovskite quantum dots(Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs)in ethanol, and constructed the environment-friendly fluorescence sensor for the quantitative detection of OTC for the first time. The results demonstrated that the fluorescence quenching degree of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs showed a good linear relationship with the concentration of OTC within the range of 2.0\u0026thinsp;~\u0026thinsp;18 \u0026micro;M, and the detection limit was 0.432 \u0026micro;M. By studying fluorescence lifetime, absorption spectroscopy, and evaluation of internal filtration parameters., it was proved that the sensing mechanism is caused by the inner filter effect owing to the overlapping of fluorescence emission spectrum of Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs and UV absorption spectrum of OTC. Moreover, Cs\u003csub\u003e3\u003c/sub\u003eBi\u003csub\u003e2\u003c/sub\u003eBr\u003csub\u003e9\u003c/sub\u003e PQDs fluorescent sensor had good selectivity and anti-interference ability. It is believed that this work will open up a new way for lead-free perovskite quantum dot fluorescence sensor in the field of analytical detection.\u003c/p\u003e","manuscriptTitle":"Environment-friendly lead-free Cs3Bi2Br9 perovskite quantum dots as fluorescent probes for rapid detection of oxytetracycline via inner filter effect","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-09-12 11:10:53","doi":"10.21203/rs.3.rs-4918535/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-09-24T08:07:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-23T01:40:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-13T18:08:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"207225184825178529367991955360200826668","date":"2024-09-02T03:15:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"99704076110827523584677222800696549619","date":"2024-08-19T15:36:05+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-16T13:20:53+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-08-16T09:18:31+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-08-16T06:09:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Cluster Science","date":"2024-08-15T09:46:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-cluster-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Journal of Cluster Science](https://www.springer.com/journal/10876) ","snPcode":"10876","submissionUrl":"https://mc.manuscriptcentral.com/jocl","title":"Journal of Cluster Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"c1a7d378-cf9a-4bb6-8644-7cdc81e96d11","owner":[],"postedDate":"September 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-11-08T19:08:27+00:00","versionOfRecord":[],"versionCreatedAt":"2024-09-12 11:10:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4918535","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4918535","identity":"rs-4918535","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}