Colorimetric and fluorescent dual-mode detection of arsenic in oysters and living cells using N/S doped carbon dots

Colorimetric and fluorescent dual-mode detection of arsenic in oysters and living cells using N/S doped carbon dots | 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 Colorimetric and fluorescent dual-mode detection of arsenic in oysters and living cells using N/S doped carbon dots Shuyang Sun, Yu Gao, Daohong Zhang, Lihong Su, Chengke Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9144608/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Arsenic (As 3+ ) contamination in food and biological systems is harmful to human health; therefore, it is urgent to develop a sensitive and rapid method for As 3+ detection. Herein, a fluorescence and colorimetric dual-mode sensing approach was developed using a nitrogen and sulfur co-doped yellow emissive carbon dots (Y-CD). The coordination of amino and sulfur groups in Y-CD with As 3+ leads to changes of the Y-CD dispersion state, which induces a significant red shift in the absorption spectra and a decrease in fluorescence intensities. A smartphone-assisted detection approach was employed for eliminating the need of sophisticated equipment. The proposed method exhibited a low detection limit of 1 mM As 3+ , rapid response within 5 minutes, and was applied for As 3+ detection in both oysters and living cells, demonstrating its robustness in complex matrices. carbon dots As3+ colorimetric fluorescence Oyster Smartphone-assisted detection Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Food safety is important to human health. With the development of modern industry, many heavy metal ions were found in seawater and seafood, e.g. , scallops and oysters [ 1 ]. In these poisonous metal ions, arsenic (As 3+ ) is harmful to human health, which may result in skin damage, circulatory system issues, protein coagulation, nerve inflammation, muscle weakness, and carcinogenicity [ 2 , 3 ]. The maximum acceptable concentration (MAC) of As 3+ is 0.5 mg/kg (equal to 6.7 µM) in fish and seafood (GB 2762 − 2022). It is important to sensitively and quickly detect As 3+ in food. The mainstream detection methods for As 3+ are spectrometric techniques, like atomic absorption spectroscopy [ 4 ], atomic fluorescence spectrometry [ 5 ], inductively coupled plasma mass spectrometry (ICP-MS) [ 6 ], and inductively coupled plasma-optical emission spectrometry [ 7 ], due to their advantages, like high sensitivity, good accuracy, and selectivity. However, the complicated operation process, sophisticated instruments, and the infeasibility for on-site applications hindered their wide applications in As 3+ detection in seafood. In terms of simplicity and cost-effectiveness, colorimetric or fluorescent detection is more practical, can be applied for real-time analysis, and provides results that can be seen by the naked eye [ 8 , 9 ]. In recent years, carbon dots (CDs) based spectrometry has been promising for biosensing. CDs have the merit of unique optical properties (colorimetric and fluorescence), easy preparation and surface modification, high compatibility, and low cost [ 3 , 10 , 11 ], which are widely used for the construction of nanoprobes. Carbon-rich compounds can be carbonized at high temperatures and form small clusters with specific fluorescent properties [ 12 , 13 ]. The element doping of CDs with N, O, and S can change the energy level and enhance their fluorescence intensity [ 14 – 16 ]. Meanwhile, due to the coordination interaction between N, O, and S with metal ions, the dispersion state and energy conversion efficiency of the CDs will be interrupted, which induces a change in the fluorescent intensity of the CDs, consequently [ 17 – 19 ]. Previous literatures had reported that CD with blue-fluorescence can be synthesized using citrate and tris(hydroxymethylmethylamine) as precursors [ 20 ], which often appeared colorless or pale-yellow under daylight, and emit blue fluorescence only under UV light, due to the color change is subtle or not easily detectable after the addition of analyte, therefore is not convenient for the colorimetric assay, and also creates obstacles for high-throughput analysis by using traditional plastic microwell plate (UV absorption is significant for polystyrene microwell plates). In contrast to the traditional blue light-emitting CDs, yellow color and red fluorescence CDs are getting more and more attention, due to the large Stokes shifts between excitation and emission wavelengths [ 3 , 21 , 22 ]. To explore the applications of yellow carbon dots (Y-CDs) for As 3+ detection in oysters and cells, here we have developed a dual-mode sensing strategy for the sensitive and selective detection of As 3+ . The colorimetric and fluorescence properties of Y-CDs were enhanced by doping them with N and S elements using thiourea as a co-precursor. After careful characterization of the Y-CDs and optimization of key experimental parameters, the method was applied for As 3+ detection in aqueous solutions and on the filter paper disk. The performance of this method was validated through recovery tests and certified ICP-MS analysis. Experimental section Reagents and instruments The o -phenylenediamine ( o -PD), m -phenylenediamine ( m -PD), and p -phenylenediamine ( p -PD) were acquired from Aladdin Co., Ltd. (Shanghai, China), the thiourea was acquired from Adamas Co., Ltd. (Shanghai, China), and the As 3+ standard solution was obtained from the National Institute of Metrology (Beijing, China) with a concentration of 1.00 mg/mL. Milli-Q water (18.2 MΩ.cm) was used throughout the experiments. All other reagents were of analytical grade unless specified otherwise. UV-visible spectra and fluorescent spectra were recorded on a Tecan Infinite 200 PRO microplate reader (Mannedorf, Switzerland). The hydrated particle size and Zeta-potential of Y-CD were measured with a NanoBrook 90Plus PALS size and zeta potential analyzer (Brookhaven Instruments, USA). Fourier transform infrared (FT-IR) spectra (4000 − 400 cm − 1 ) were recorded with an IR Tracer-100 spectrometer (Shimadzu Co., Ltd, Japan) using the KBr pellet technique. The transmission electron microscope (TEM) images were acquired by an HT-7800 transmission electron microscope (Hitachi Co., Ltd., Japan), and the X-ray photoelectron spectroscopy (XPS) measurements were conducted using an AXIS Ultra DLD X-ray photoelectron spectrophotometer (Shimadzu Co., Ltd., Japan). Preparation of Y-CD The Y-CD was synthesized according to the previous methods with some modifications [ 23 – 25 ]. Briefly, 0.1 g o -PD and 0.2 g thiourea were mixed in 20 mL of ethanol and stirred for 30 min; the mixture was moved to a 50 mL autoclave, heated at 180 oC for 8 h. The product was dialyzed using a dialysis bag (molecular cut off is 10000) for 8 h to remove the unreacted small molecules. The solutions left in the dialysis bag were further centrifuged at 10000 rounds per minute (rpm) for 10 min to remove the potentially large aggregates, the supernatants were transferred to a glass bottle, and stored at 4 o C. Other CDs were synthesized by a similar protocol by changing o -PD to p -PD or m -PD in the presence or absence of thiourea. Measurements of As in aqueous solutions 100 µL Y-CD was mixed with different concentrations of As 3+ , after reacting for 1 min, the UV-visible absorption spectra were recorded with the wavelength from 300 to 600 nm, and fluorescent spectra were also recorded with the emission wavelength between 450 and 750 nm and the excitation wavelength at 433 nm. Measurements of As using smartphone-assisted method The round filter paper disk with a diameter of 8 mm was obtained using a handheld puncher (Kamei Co., Yiwu, China), then the paper disks were immersed in the Y-CD solution for 2 min, and taken out to dry in the air. Next, 15 µL solutions with different concentrations of As 3+ were dropped onto the paper disk. After the paper disk dried naturally, photos of the disks were acquired under daylight and under ultraviolet light (365 nm). The green channel signal values of aqueous solution and paper disk photos were acquired using Adobe Photoshop software (Version 7.0.1). Measurements of As in oyster samples The oyster was purchased from a local supermarket (Yantai, China), and the oyster meat was carefully removed using a cereal knife and treated using conventional acid-assisted digestion [ 26 ]. Briefly, 5 g fresh oyster meat was dried at 105 o C until the weight was not changed, then this product was ground to powder, and added into 5 mL HNO 3 and 0.5 mL H 2 O 2 (30% w/w) in an autoclave, heated at 180 o C for 5 h, after removing the lid of autoclave, the solutions were heated at 100 o C to remove the acid completely, the product was further dissolved in 1 mL water, centrifuged at 13000 rpm for 5 min to remove the potential large precipitate, the supernatant was carefully transferred to a glass bottle and stored at 4 o C. The As 3+ was detected using the standard additional method by adding different amounts of the As 3+ standard solution into the pretreated actual samples. Measurements of As 3+ in breast cancer cells 4T1 mouse breast cancer cells were grown with fresh Dulbecco’s Modified Eagle’s medium (DMEM), supplemented with 10% fetal bovine serum in a humidified 5% CO 2 incubator at 37 o C. After the cells were cultured with different concentrations of Y-CD for 8 h, the cell viability was measured using a cell counting kit-8 (Beyotime Biotechnology Co., Hangzhou, China) following the manufacturer’s instructions. After the 4T1 cells were incubated with different concentrations of As 3+ for 2 h, 1 mg/mL Y-CD was added and incubated with the cells for another 2 h. After the cells were washed with PBS 3 times, they were treated with 2.5% (v/v) glutaraldehyde (Yuanye Biotechnology Co., Shanghai, China) for 10 min, and DAPI (4’,6-diamidino-2’-phenylindole) cell staining solution (Beyotime Biotechnology Co., Hangzhou, China) for another 10 min to stain the cell nucleus. After washing the cells using PBS 3 times, the fluorescent images of 4T1 cells were acquired using a Yokogawa CSU-W1 spinning disk field scanning confocal system (Nikon Instruments Inc.). Results and discussion Characterization of fluorescent Y-CD Y-CD was prepared through the carbonization process using an o -PD and thiourea as precursors; the overall synthetic procedure of the Y-CD and the As 3+ detection process is shown in Scheme 1 . The characterization results of our prepared Y-CD were shown in Fig. 1 . The TEM image in Fig. 1 a indicated that small-sized sphere nanoparticles with a diameter of ∼10 nm were prepared. The surface functional groups on the Y-CD were measured by FT-IR analysis (Fig. 1 b), the broad peak at 3100 cm − 1 indicated the presence of hydroxyl and amine functional groups, the peak at 1600 cm − 1 represents C = O of the amide/N-H groups, and the peak around 1000 cm − 1 C-H represents in-plane bending vibration of the benzene ring which comes from the o -PD (marked with blue strip). The strong peaks at 1450 cm − 1 and 750 cm − 1 originated from the stretch vibration and in-plane deformation vibration of C = S coupled with N-H bending in a hydrogen-bonded structure (marked with a yellow strip), the functional groups containing carbon and sulfur originated from polymerization followed by carbonization of o -PD and thiourea [ 3 ]. Meanwhile, the successful incorporation of S and N atoms into the carbon-rich Y-CD was confirmed by the XPS measurement (Figs. 1 c-f), wide-scan XPS spectrum shows peaks at 162, 287, 400, and 532 eV, which correspond to S2p, C1s, N1s and O1s, respectively [ 17 ]. These results indicated that the N/S co-doped CD was successfully prepared. The spectroscopic measurement results of Y-CD were shown in Figs. 1 g and h, the Y-CD had a strong absorption between 300–600 nm with a maximum absorbance at about 420 nm and a strong fluorescence between 450–750 nm (Fig. 1 g). Especially, the maximum fluorescence emission wavelength was not affected by changing the excitation wavelength (Fig. 1 h), which was different from many blue-emission CDs [ 20 ], in which the maximum emission wavelengths were red-shifted by increasing the excitation wavelength; therefore, it was beneficial for the application of Y-CD if considering the instrument differences in different laboratories. The feasibility experiments As shown in Fig. 1 i, the Y-CD was yellow in color under daylight, and emitted red fluorescence (λ em = 575 nm) under the excitation wavelength of 433 nm (the Stokes shift of the wavelength is 142 nm). To demonstrate that the Y-CD could be used for As 3+ detection, the As 3+ standard solution was mixed with the Y-CD, and the color of Y-CD changed from pale-yellow to deep yellow, and the maximum absorbance wavelength was also red-shifted, accompanied by an increase in absorbance. On the contrary, after the addition of As 3+ into Y-CD solution, the fluorescence spectra of Y-CD solutions decreased significantly along with the maximum emission wavelength undergoing a slight blue shift, and the fluorescence images of Y-CD also changed from luminous yellow to dark yellow under UV light (365 nm). These results indicated the Y-CD could be used for As 3+ detection through colorimetric and fluorescent methods. The mechanism of As 3+ detection To explore the detection mechanism of Y-CD for As 3+ , different CDs were prepared using o -PD, m -PD, p -PD and thiourea as the precursor through similar synthetic procedures. As shown in Figs. S1a-c, only o -PD yielded a distinct UV-Vis absorption peak, whereas m -PD produced broad UV absorption without a defined peak, suggesting irregular morphology of the nanoparticle [ 19 ]. The p -PD system showed a broad absorption peak between 400 and 500 nm, indicating a heterogeneous particle size detrimental to the colorimetric assay. Co-doping with sulfur ( via thiourea) significantly enhanced the absorption of Y-CDs by forming localized energy transfer centers, confirming that S doping can alter the internal energy level of the material, and facilitating electron transfer [ 17 ]. Upon the addition of As 3+ , S-doped o -PD CDs exhibited a pronounced redshift (∼26 nm) versus non-doped o -PD CDs (∼8 nm). This enhanced spectral shift was attributed to S-doping increasing the binding affinity for As 3+ due to the high affinity of the S atom for As 3+ [ 8 ], reducing electron migration energy levels via a stronger static quenching process [ 3 ]. In contrast, the m -PD derived CDs showed no significant spectral changes even with thiourea co-precursor. This might be due to the substantial intramolecular distance between amino groups of m -PD impeding effective complex formation with As³⁺ [ 27 ]. Meanwhile, p -PD systems exhibited modest spectral variation upon As³⁺ addition, but S co-doping induced an observable redshift of spectra accompanied by the emergence of novel absorption features (∼525 nm). This phenomenon indicates that amino groups from adjacent p -PD molecules undergo head-to-head intermolecular interactions with As³⁺, alongside the S doping incorporated from thiourea, forming durable N-(S-)As 3+ -N complexes [ 3 ]. These results collectively demonstrate S incorporation is crucial for optimizing As³⁺ detection performance. Furthermore, the spatial arrangement of amino groups in the carbon dots significantly modulates binding affinity and complex stability, thereby influencing the overall detection efficiency [ 28 ]. The fluorescence properties of CDs derived from different precursors were also systematically analyzed. As shown in Fig. 1 d, o-PD based CDs exhibited a fluorescence emission peak at ∼575 nm, while the peak position remained unchanged with S co-doping. The fluorescence intensity increased by approximately 1.7-fold, supporting the formation of intramolecular fluorophores upon thiourea addition, therefore enhancing As 3+ detection. In contrast, as shown in Fig. S1 d, m -PD based CDs showed a weaker fluorescence emission with the peak at 500 nm. Notably, the fluorescence intensity was significantly enhanced when m -PD and thiourea were employed as co-precursors, which is consistent with the previously observed enhancing effect of S co-doping on fluorescence signals [ 17 ]. However, p -PD-derived CDs showed no significant fluorescence emission regardless of S co-doping using thiourea as co-precursor, which was due to the irregular morphology of CDs and the pronounced internal filter effect contributing to fluorescence quenching. The hydrodynamic size and zeta potential of Y-CD were also measured to further study the interaction of Y-CD with As 3+ , which were 4.86 nm and − 56.2 mV, respectively. After the addition of As 3+ , the hydrodynamic size and zeta potential of Y-CD-As 3+ were increased to 209.57 nm and 10.50 mV, further confirmed the binding between the amino groups and sulfur atoms with As 3+ , this binding induced the aggregation of Y-CD and also altered the surface charge of the materials to a positive value due to the presence of positively charged As 3+ , which was consistent with the previous reports that dithiothreitol [ 8 ] or thiodiacetic acid [ 9 ] conjugated nanoparticles have high affinity with As 3+ . Our experimental findings demonstrated that Y-CD can effectively interact with As 3+ via the reaction between amino groups and sulfur atoms, which leads to static quenching, resulting in a reduction of electron transition energy and a redshift of the maximum absorption wavelength with increased absorbance. Additionally, during the electron transition between the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), the interaction between electrons and the positively charged As 3+ promotes an energy relaxation process, which leads to the deactivation of the excited state, ultimately quenching the fluorescence signals. These results are consistent with previous literature reports [ 3 , 17 ]. The optimization experiments To improve the detection performance of the method, different experimental conditions were optimized. As shown in Figs. 2 a, the fluorescent spectra of Y-CD were measured in solutions of different pH in the absence and presence of As 3+ ; the fluorescence signals of solutions decreased slowly as the pH decreased from 10 to 4, regardless of whether there was As 3+ or not; however, at pH 5, the fluorescence spectra decreased significantly in the presence of As 3+ . Similarly, the absorbance spectra of solutions were also red-shifted as the pH decreased, and the spectral difference reached a maximum at pH 5 (Fig. S2a). To conveniently evaluate the effect of pH on the detection of As 3+ , the maximum fluorescence intensity of fluorescent spectra and the absorbance ratio of absorption spectra at 416 nm and 452 nm (A416nm/A452nm) were used, as shown in Figs. 2 b and S2b, the most significant differences between the two solutions in the absence and presence of As 3+ were observed at pH 5. The low fluorescent intensity of Y-CD alone in acidic solution was ascribed to the interaction of the surface-attached functional groups with H + ions and might induce the destruction of fluorescence generating units of Y-CD, which is consistent with previous reports [ 3 ]. Since the As 3+ could interact with Y-CD and induce a change in its dispersion state, the Y-CD concentration was also optimized to increase the alterations in absorption and fluorescent signals, therefore improving the detection sensitivity of As 3+ . As shown in Figs. 2 c-d and S2c-d, the spectra changed more significantly with increasing the Y-CD concentration from 0.15 mg/mL to 4.8 mg/mL, while they became less obvious if the Y-CD concentration was more than 0.6 mg/mL. It was interesting to find that even after mixing As 3+ with Y-CD for 0.5 min, the spectra were quickly changed and kept at a stable state from 0.5 min to 18.5 min (see Figs. 2 e-f and S2e-f). Therefore, in the following experiment, the pH of the solution was selected as 5, the concentration of Y-CD was 0.6 mg/mL, and the reaction time between Y-CD and As 3+ was determined as 5 min to facilitate the experimental operation. Detection of As 3+ in aqueous solution To verify the ability of the Y-CD-based detection method for As 3+ detection, different concentrations of As 3+ were added to Y-CD solutions. As shown in Fig. 3 a, the fluorescence of Y-CD decreased gradually with increasing the concentration of As 3+ from 1 µM to 25 µM, and remained at a very low level if more than 25 µM As 3+ was added. The fluorescence images of Y-CD interact with different concentrations of As 3+ also showed a decrease in intensity (The samples were irradiated using a single wavelength LED light at 465 nm). The fluorescence intensities of Y-CDs at 575 nm had a linear response toward the logarithm of the concentration of As 3+ ([As 3+ ]) from 2.5 µM to 25 µM (see Fig. 3 b), while the regression equation can be expressed as F = 63141–42243 log [As 3+ ] (µM) (r 2 = 0.988), and the limit of detection and limit of quantification were estimated as 1 µM and 3.3 µM, respectively (S/N = 3). Similarly, the absorption spectra of Y-CD in the presence of As 3+ were also measured, as shown in Fig. 3 c, the yellow color of Y-CD solution was enhanced and the absorption spectra were gradually red-shifted with increasing the amounts of As 3+ from 2.5 µM to 25 µM, the absorbance ratios of Y-CDs at 416 nm and 452 nm (A416nm/A452nm) were also decreased gradually between 2.5 µM to 25 µM (see Fig. 3 d), the regression equation can be expressed as A416nm/A452nm = 1.632–0.704 log [As 3+ ] (µM) (r 2 = 0.984), and the limit of detection and limit of quantification were estimated to 1 µM and 3.3 µM, respectively (S/N = 3). This method has advantages like being easier to conduct, cost and time efficiency. According to the national food safety standard for As 3+ element, the MAC of As 3+ was 6.7 µM in fish and seafood; therefore, our method could be used for easily determining the safety of food. Selectivity experiment The selectivity of this method was also evaluated by adding different kinds of interferences, including metal ions, proteins, peptides, amino acids, and carbohydrates, as shown in Figs. 3 e-f, the common proteins, peptides, amino acids, carbohydrates, sodium ascorbate, dopamine, and many metal ions (Ca 2+ , Ni 2+ , Zn 2+ , NH 4 + , Hg 2+ , Pb 2+ , Na + , K +, and Mg 2+ ) had a negligible impact on the Y-CD spectra. We also observed that the Fe 2+ and Fe 3+ induced the fluorescence intensity of Y-CD to decrease, Fe 2+ , Fe 3+ and Cu 2+ induced the absorption spectra red-shifted to some extent (see Fig. S3). This phenomenon might be induced by the coordination of metal ions with Y-CD, resulting in a change in the dispersion state of Y-CD. To eliminate the interference of Fe 2+ , Fe 3+ and Cu 2+ on the As 3+ detection, EDTA was used as the masking agent in this system, as shown in Fig. S4. With the addition of EDTA, the impacts of Fe 2+ , Fe 3+ and Cu 2+ on the Y-CD spectra were eliminated. Due to the very weak bonding capacity of EDTA with As 3+ , the spectra of Y-CD were not changed regardless of whether EDTA was added along with As 3+ or not. In general, we might demonstrate that our method had reasonable selectivity for As 3+ detection. Detection of As 3+ using smartphone-assisted method To simplify the As 3+ detection process, different concentrations of As 3+ were added into Y-CD solutions or Y-CD contained filter paper disk, and the photos of solutions were acquired under daylight or ultraviolet light using a smartphone. As shown in Fig. 4 , with increasing the concentrations of As 3+ , the color of the solutions/paper disks changed from yellow to brown, while their fluorescent intensities were also decreased, which can be observed by the naked eye; this phenomenon was consistent with the above-mentioned experiment results. To quantitatively determine the amounts of As 3+ , the green channel signal intensities of each photo were extracted using Photoshop software, the signal intensity decreased with increasing the concentrations of As 3+ from 2 µM to 20 µM, and the linear regression equations are I = 226.63–105.24 log[As 3+ ] (µM), (r 2 = 0.982) for As 3+ detection in solutions (color change measurement), I = 292.63–142.24 log[As 3+ ] (µM), (r 2 = 0.992) for As 3+ detection in solutions (fluorescence change measurement), I = 139.25–55.86 log[As 3+ ] (µM), (r 2 = 0.996) for As 3+ detection on paper strip disks (color change measurement), and I = 251.74–116.46 log[As 3+ ] (µM), (r 2 = 0.992) for As 3+ detection on paper strip disks (fluorescence change measurement). By this means, we have developed a more convenient and cost-efficient method for As 3+ determination with comparable detection capabilities. Detection of As 3+ in the actual sample To demonstrate the application of this method for actual sample detection, high-temperature acid digestion methods were used to pretreat three kinds of oysters, then different amounts of As 3+ were added based on the standard addition method. As shown in Figs. S5a-b, the fluorescence intensity of Y-CD decreased with increasing concentrations of As 3+ in the oyster samples, the regression function for As 3+ detection was F = 62712–2595 [As 3+ ] (µM), (r 2 = 0.999). A similar phenomenon was also observed by measuring the absorption spectra of solutions, as shown in Figs. S5c-d, the absorbance spectra were red-shifted with the addition of As 3+ in the oyster samples, and the regression function for As 3+ detection was A416nm/A452nm = 1.156–0.0149 [As 3+ ] (µM), (r 2 = 0.999). Furthermore, 0, 6, and 15 µM As 3+ were added into 3 kinds of oysters to examine the performance of our dual-mode detection method, as shown in Table 1 , the recoveries of our proposed method were between 95% to 112%. It should be noted that a naked-eye distinguishable color or fluorescence was observed if the As 3+ exceeded the MAC (data not shown). In addition, the samples were also detected using the ICP-MS method, and a good correlation among the colorimetric method, fluorescent method, and ICP-MS was obtained. Hence, our method not only shortened the detection time and simplified the whole operating process, but also provided a dual-mode method for As 3+ detection in actual samples. Table 1 Analyses of As 3+ in oyster samples (mean ± SD, µmol kg − 1 of wet weight). Species Add (µM) Method comparison ICP-MS This method UV-Vis Recovery (%) Fluorescence Recovery (%) Sample 1 0 0.01 0.02±0.01 N/D 0.01±0.03 N/D 6 6.3 6.5±0.3 108 5.8±0.3 97 15 15.9 15.8±0.4 105 15.5±0.4 103 Sample 2 0 N/D 0.05±0.02 N/D 0.04±0.03 N/D 6 5.9 5.8±0.5 97 6.7±0.6 112 15 14.5 14.7±0.4 98 15.7±0.5 105 Sample 3 0 N/D 0.04±0.02 N/D 0.02±0.03 N/D 6 6.4 6.4±0.4 107 5.7±0.4 95 15 15.7 14.5±0.5 97 15.3±0.5 102 Detection of As 3+ in cancer cells To further investigate the application of Y-CD for As 3+ detection in living cells, different concentrations of Y-CD were first incubated with 4T1 breast cancer cells, as shown in Fig. 5 , cell viability remained above 80% with Y-CD concentrations up to 3.5 mg/mL. After the 4T1 cells were incubated with different concentrations of As 3+ , they were further stained with Y-CD. The fluorescent signal intensity of Y-CD decreased with the concentration of As 3+ increased from 0 µM to 30 µM, there was also no fluorescent signal in the absence of Y-CD. The overall experiment result indicated that Y-CD could serve as a good candidate for As 3+ detection in the living cell system, which is meaningful for human health risk assessment. Conclusion In summary, a dual-mode method was developed for As 3+ detection by investigating the fluorescence and color changes of Y-CD in the presence of As 3+ . The Y-CD probe was synthesized conveniently by employing o -PD and thiourea as the precursor. The amino and sulfur atoms could coordinate with As 3+ , which resulted in the dispersion state changes of Y-CD, and further resulted in the red-shift of absorption spectra and decrease of fluorescence intensity of Y-CD. As low as 1 µM As 3+ could be detected without a sophisticated instrument in less than 5 min. Especially, our method could be used for As 3+ detection in aquatic products and cancer cells, which is meaningful for food safety measurement and human health risk assessment. Declarations Supplementary Information The online version contains supplementary material available at https://doi.org/. Funding This study was funded by the Natural Science Foundation of Shandong Province (ZR2023MC178) and the Youth Innovation Technology Project of Higher School in Shandong Province (Food Nanotechnology Innovation Team). Author contribution Shuyang Sun: methodology, writing—review and editing. Yu Gao: formal analysis, software. Daohong Zhang: conceptualization. Lihong Su: investigation. Chengke Wang: supervision, writing—review and editing. Data availability Data will be made available on request. Declarations The authors declare no competing financial interests. 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D, Selvaraj M, Saritha A (2025) Advances in doped carbon quantum dots: synthesis, mechanisms, and applications in sensing technologies. Chem Eng J 514:163262. Wang C, Tan R, Chen D (2018) Fluorescence method for quickly detecting ochratoxin A in flour and beer using nitrogen doped carbon dots and silver nanoparticles. Talanta 182:363–370. Fernández-Merino A, Chávez M, Sánchez-Obrero G, Madueño R, Blázquez M, Del Caño R, Pineda T (2024) Fluorescent carbon dots with red emission: A selective sensor for Fe(III) ion detection. Chemosensors 12:226. Safarpoor M, Dinarvand R, Ghaedi M, Asfaram A (2025) Carbon dots with red emission as nanoprobe for sensing of heparin in biofluids and pharmaceutical samples. RSC Adv 15:2217–2223. Liu Q-L, Niu X-Y, Xie K-X, Yan Y-M, Ren B-R, Liu R-R, Li Y-X, Li L (2021) Fluorescent carbon dots as nanosensors for monitoring and imaging Fe³⁺ and HPO₄²⁻ ions. ACS Appl Nano Mater 4:190–197. Fan P-F, Liu C, Hu C-C, Li F-F, Lin X, Xiao F-B, Liang H, Li L, Yang S-Y (2022) Orange-emissive N,S-co-doped carbon dots for label-free and sensitive fluorescence assay of vitamin B₁₂. New J Chem 46:877–882. Wang Z-Y, Tong Y-S, Liu B-H, Dong C, Yan J-W, Niu W-F (2025) A novel label-free carbon dots-based fluorescent aptamer sensor for the detection of fentanyl. Spectrochim Acta A 340:126338. Zhang W, Chen Z-Y, Guan Y-F, Liu C, Zheng K-Y, Zou X-B (2021) Aptamer-functionalized screen-printed electrode coupled with graphene oxide and methylene blue nanocomposite as enhanced signal label for total arsenic determination in shellfish. Sens Actuators B Chem 335:129383. He P, Bai J, Yang G, Qin F, Wang X, Yu X, Yao Y, Tang X, Ren L (2025) Regulation of the unconventional luminescence behaviors of phenylenediamine-based carbon dots with high PLQY values. Chem Eng J 506:160342. Jiang K, Sun S, Zhang L, Lu Y, Wu A, Cai C, Lin H (2015) Red, green, and blue luminescence by carbon dots: full-color emission tuning and multicolor cellular imaging. Angew Chem Int Ed 54:5360–5363. Additional Declarations No competing interests reported. Supplementary Files Supportinginformation.docx GraphicalAbstract.png Graphical Abstract Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9144608","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":612798647,"identity":"d6e93806-a1a0-42e0-bf50-d59f6fd9bebf","order_by":0,"name":"Shuyang Sun","email":"","orcid":"","institution":"Ludong University","correspondingAuthor":false,"prefix":"","firstName":"Shuyang","middleName":"","lastName":"Sun","suffix":""},{"id":612798648,"identity":"07405ae0-db7a-4ff6-860c-c84a8d74c522","order_by":1,"name":"Yu Gao","email":"","orcid":"","institution":"Ludong University","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Gao","suffix":""},{"id":612798649,"identity":"e2a98d0e-3df1-4b52-b2d2-49b957119562","order_by":2,"name":"Daohong Zhang","email":"","orcid":"","institution":"Ludong University","correspondingAuthor":false,"prefix":"","firstName":"Daohong","middleName":"","lastName":"Zhang","suffix":""},{"id":612798650,"identity":"88631f96-477d-4de9-8613-fd3513e593d6","order_by":3,"name":"Lihong Su","email":"","orcid":"","institution":"Ludong University","correspondingAuthor":false,"prefix":"","firstName":"Lihong","middleName":"","lastName":"Su","suffix":""},{"id":612798651,"identity":"55f58362-bc23-4b33-85b6-095b9ec72085","order_by":4,"name":"Chengke Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYDACCRBxAMxkfJBQUUOaFmaDB2eOkaaFTfJhCzNhHfyzm489/HLGJrF/dvu1isQGNgb+9u4E/JbcOZZuLHMjLXHGnTNlNxJ3yDBInDm7Aa8WA4kcM2mJD4dzG27kpN1IPMMGFMklpCX/G1DL/9z5QC0FiW3MxGjJYZP8cONA7oYb6ccYiNIicSPNTJrhTHL9xhs5zBIJZ47xEPQL/4zkZ5I/jtkZy91If/jxR0WNHH97L34tIMDMA6Z4DMAkQeUgwPgDTLE/IEr1KBgFo2AUjDwAAI9UUNtcIEhCAAAAAElFTkSuQmCC","orcid":"","institution":"Ludong University","correspondingAuthor":true,"prefix":"","firstName":"Chengke","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2026-03-17 06:08:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9144608/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9144608/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105594510,"identity":"66ce53c2-69d6-4eae-9940-1318284740e4","added_by":"auto","created_at":"2026-03-27 17:29:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":259765,"visible":true,"origin":"","legend":"\u003cp\u003eThe Y-CD characterization experiment. (\u003cstrong\u003ea\u003c/strong\u003e) The TEM image of Y-CD, (\u003cstrong\u003eb)\u003c/strong\u003e the FT-IR spectra of \u003cem\u003eo\u003c/em\u003e-PD, thiourea and Y-CD, (\u003cstrong\u003ec-f\u003c/strong\u003e) the XPS of Y-CD and \u003cstrong\u003eb\u003c/strong\u003e the absorption, excitation and emission spectra of Y-CD, (\u003cstrong\u003eh\u003c/strong\u003e) the fluorescence emission spectra recorded at various excitation wavelengths, and inset of (\u003cstrong\u003eh\u003c/strong\u003e) indicates the maximum fluorescence intensity of Y-CD at different excitation wavelengths. (\u003cstrong\u003ei\u003c/strong\u003e) the absorption and fluorescence spectra of Y-CD in the absence and presence of As\u003csup\u003e3+\u003c/sup\u003e. The inset images of (\u003cstrong\u003ei\u003c/strong\u003e) indicate the Y-CD solution under daylight (left) or irradiated with 365 nm UV light (right).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/010bce19785f10843073891e.png"},{"id":105594512,"identity":"e449e10a-6d96-486a-84c5-c4dfcb7c2089","added_by":"auto","created_at":"2026-03-27 17:29:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":164466,"visible":true,"origin":"","legend":"\u003cp\u003eThe detection condition optimization experiment. (\u003cstrong\u003ea\u003c/strong\u003e) The fluorescence spectra of Y-CD at different pH in the absence and presence of As\u003csup\u003e3+\u003c/sup\u003e, (\u003cstrong\u003eb\u003c/strong\u003e) the fluorescence intensity of Y-CD at 575 nm in solutions of different pH in the absence and presence of As\u003csup\u003e3+\u003c/sup\u003e, (\u003cstrong\u003ec\u003c/strong\u003e) the fluorescence spectra of different concentrations of Y-CD in the absence and presence of As\u003csup\u003e3+\u003c/sup\u003e, (\u003cstrong\u003ed\u003c/strong\u003e) the fluorescence intensity of different concentrations of Y-CD at 575 nm in the absence and presence of As\u003csup\u003e3+\u003c/sup\u003e, (\u003cstrong\u003ee\u003c/strong\u003e) the fluorescence spectra of Y-CD after adding As\u003csup\u003e3+\u003c/sup\u003e for different time, (\u003cstrong\u003ef\u003c/strong\u003e) the fluorescence intensity of Y-CD at 575 nm after adding As\u003csup\u003e3+\u003c/sup\u003e for different time. The error bars represent the relative standard deviation of three experimental results.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/678b1eed982fc0ac71886d2d.png"},{"id":105728189,"identity":"a5242c4a-28f8-4502-8295-f0f62eb543e2","added_by":"auto","created_at":"2026-03-30 11:10:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":189609,"visible":true,"origin":"","legend":"\u003cp\u003eThe As\u003csup\u003e3+\u003c/sup\u003e measurement and selectivity experiment. (\u003cstrong\u003ea\u003c/strong\u003e) The fluorescence and (\u003cstrong\u003ec\u003c/strong\u003e) absorption spectra of Y-CD in the presence of different concentrations of As\u003csup\u003e3+\u003c/sup\u003e, (\u003cstrong\u003eb\u003c/strong\u003e) the fluorescence intensity of Y-CD at 575 nm and (\u003cstrong\u003ed\u003c/strong\u003e) the ratio of absorbance at 416 nm and 452 nm of Y-CD in the presence of different concentrations of As\u003csup\u003e3+\u003c/sup\u003e. Inset of (\u003cstrong\u003eb\u003c/strong\u003e) indicates the fluorescence image of Y-CD irradiated with 465 nm light, Inset of (\u003cstrong\u003ed\u003c/strong\u003e) indicates the image of Y-CD under daylight. The concentrations of As\u003csup\u003e3+\u003c/sup\u003e in the Y-CD are 0, 2.5, 5, 7.5, 10, and 25 mM, respectively (from left to right). (\u003cstrong\u003ee\u003c/strong\u003e) The fluorescence spectra of Y-CD in the presence of different species, and (\u003cstrong\u003ef\u003c/strong\u003e) the corresponding fluorescence intensity of Y-CD at 575 nm in the presence of different species. The error bars represent the relative standard deviation of three experimental results.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/0afc61d905180e2513931525.png"},{"id":105728282,"identity":"341aded5-8711-4495-9358-4654744254fc","added_by":"auto","created_at":"2026-03-30 11:11:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":136060,"visible":true,"origin":"","legend":"\u003cp\u003eThe As\u003csup\u003e3+\u003c/sup\u003e measurement using the smartphone-assisted method. The linear relationship between green channel signal intensity of colorful (\u003cstrong\u003ea\u003c/strong\u003e and \u003cstrong\u003ec\u003c/strong\u003e) and fluorescent (\u003cstrong\u003eb\u003c/strong\u003e and \u003cstrong\u003ed\u003c/strong\u003e) images and As\u003csup\u003e3+\u003c/sup\u003e concentrations from 2 mM to 20 mM. The error bars represent the relative standard deviation of three experimental results. Inset shows the color changes (\u003cstrong\u003ea\u003c/strong\u003e and \u003cstrong\u003ec\u003c/strong\u003e) and fluorescent photos (\u003cstrong\u003eb\u003c/strong\u003e and \u003cstrong\u003ed\u003c/strong\u003e) of solutions/filter paper disks, the concentrations of As\u003csup\u003e3+\u003c/sup\u003e are 2, 4, 6, 8, 10, 20 mM, respectively (from left to right).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/8555d6fec4e4aaaff32cb058.png"},{"id":105594514,"identity":"11b087cf-c87f-4d0f-a31c-0b3b179e56b8","added_by":"auto","created_at":"2026-03-27 17:29:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":399702,"visible":true,"origin":"","legend":"\u003cp\u003eThe fluorescent imaging experiment for As\u003csup\u003e3+\u003c/sup\u003e detection in 4T1 cells. (\u003cstrong\u003ea\u003c/strong\u003e) the bright field micrographs of 4T1 cells (first line), the fluorescent images of 4T1 cells after staining with Y-CD (second line), DAPI (third line), and the merged images. The 4T1 cells were incubated with 1 mg/mL Y-CD after interacting with different concentrations of As\u003csup\u003e3+\u003c/sup\u003e. (\u003cstrong\u003eb\u003c/strong\u003e) the cell viability of 4T1 cells incubated with different concentrations of Y-CD. (\u003cstrong\u003ec\u003c/strong\u003e) the calculated fluorescent intensity of 4T1 cells (Y-CD fluorescence channel) after interacting with As\u003csup\u003e3+\u003c/sup\u003e. The error bars represent the relative standard deviation of three experimental results.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/11f4f3bdadb878a338f37553.png"},{"id":108144703,"identity":"2957e036-bb16-4f45-b649-2e05dc4fd479","added_by":"auto","created_at":"2026-04-29 20:39:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1378592,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/68a41ca4-1b0a-401a-88ff-699c71281dab.pdf"},{"id":105594515,"identity":"450c9bf6-2c09-4065-9d6c-6cff3b64aa91","added_by":"auto","created_at":"2026-03-27 17:29:55","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":555378,"visible":true,"origin":"","legend":"","description":"","filename":"Supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/40d47094eb53dfe5da0665ed.docx"},{"id":105728150,"identity":"2c6ee74d-5a3a-4b46-ab2d-ce2e292e4393","added_by":"auto","created_at":"2026-03-30 11:10:16","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":222109,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGraphical Abstract\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"GraphicalAbstract.png","url":"https://assets-eu.researchsquare.com/files/rs-9144608/v1/115cf5b9bdb05045f2b91a4b.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Colorimetric and fluorescent dual-mode detection of arsenic in oysters and living cells using N/S doped carbon dots","fulltext":[{"header":"Introduction","content":"\u003cp\u003eFood safety is important to human health. With the development of modern industry, many heavy metal ions were found in seawater and seafood, \u003cem\u003ee.g.\u003c/em\u003e, scallops and oysters [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In these poisonous metal ions, arsenic (As\u003csup\u003e3+\u003c/sup\u003e) is harmful to human health, which may result in skin damage, circulatory system issues, protein coagulation, nerve inflammation, muscle weakness, and carcinogenicity [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The maximum acceptable concentration (MAC) of As\u003csup\u003e3+\u003c/sup\u003e is 0.5 mg/kg (equal to 6.7 \u0026micro;M) in fish and seafood (GB 2762\u0026thinsp;\u0026minus;\u0026thinsp;2022). It is important to sensitively and quickly detect As\u003csup\u003e3+\u003c/sup\u003e in food. The mainstream detection methods for As\u003csup\u003e3+\u003c/sup\u003e are spectrometric techniques, like atomic absorption spectroscopy [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], atomic fluorescence spectrometry [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], inductively coupled plasma mass spectrometry (ICP-MS) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and inductively coupled plasma-optical emission spectrometry [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], due to their advantages, like high sensitivity, good accuracy, and selectivity. However, the complicated operation process, sophisticated instruments, and the infeasibility for on-site applications hindered their wide applications in As\u003csup\u003e3+\u003c/sup\u003e detection in seafood. In terms of simplicity and cost-effectiveness, colorimetric or fluorescent detection is more practical, can be applied for real-time analysis, and provides results that can be seen by the naked eye [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn recent years, carbon dots (CDs) based spectrometry has been promising for biosensing. CDs have the merit of unique optical properties (colorimetric and fluorescence), easy preparation and surface modification, high compatibility, and low cost [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], which are widely used for the construction of nanoprobes. Carbon-rich compounds can be carbonized at high temperatures and form small clusters with specific fluorescent properties [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The element doping of CDs with N, O, and S can change the energy level and enhance their fluorescence intensity [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Meanwhile, due to the coordination interaction between N, O, and S with metal ions, the dispersion state and energy conversion efficiency of the CDs will be interrupted, which induces a change in the fluorescent intensity of the CDs, consequently [\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePrevious literatures had reported that CD with blue-fluorescence can be synthesized using citrate and tris(hydroxymethylmethylamine) as precursors [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], which often appeared colorless or pale-yellow under daylight, and emit blue fluorescence only under UV light, due to the color change is subtle or not easily detectable after the addition of analyte, therefore is not convenient for the colorimetric assay, and also creates obstacles for high-throughput analysis by using traditional plastic microwell plate (UV absorption is significant for polystyrene microwell plates). In contrast to the traditional blue light-emitting CDs, yellow color and red fluorescence CDs are getting more and more attention, due to the large Stokes shifts between excitation and emission wavelengths [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo explore the applications of yellow carbon dots (Y-CDs) for As\u003csup\u003e3+\u003c/sup\u003e detection in oysters and cells, here we have developed a dual-mode sensing strategy for the sensitive and selective detection of As\u003csup\u003e3+\u003c/sup\u003e. The colorimetric and fluorescence properties of Y-CDs were enhanced by doping them with N and S elements using thiourea as a co-precursor. After careful characterization of the Y-CDs and optimization of key experimental parameters, the method was applied for As\u003csup\u003e3+\u003c/sup\u003e detection in aqueous solutions and on the filter paper disk. The performance of this method was validated through recovery tests and certified ICP-MS analysis.\u003c/p\u003e"},{"header":"Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eReagents and instruments\u003c/h2\u003e \u003cp\u003eThe \u003cem\u003eo\u003c/em\u003e-phenylenediamine (\u003cem\u003eo\u003c/em\u003e-PD), \u003cem\u003em\u003c/em\u003e-phenylenediamine (\u003cem\u003em\u003c/em\u003e-PD), and \u003cem\u003ep\u003c/em\u003e-phenylenediamine (\u003cem\u003ep\u003c/em\u003e-PD) were acquired from Aladdin Co., Ltd. (Shanghai, China), the thiourea was acquired from Adamas Co., Ltd. (Shanghai, China), and the As\u003csup\u003e3+\u003c/sup\u003e standard solution was obtained from the National Institute of Metrology (Beijing, China) with a concentration of 1.00 mg/mL. Milli-Q water (18.2 MΩ.cm) was used throughout the experiments. All other reagents were of analytical grade unless specified otherwise.\u003c/p\u003e \u003cp\u003eUV-visible spectra and fluorescent spectra were recorded on a Tecan Infinite 200 PRO microplate reader (Mannedorf, Switzerland). The hydrated particle size and Zeta-potential of Y-CD were measured with a NanoBrook 90Plus PALS size and zeta potential analyzer (Brookhaven Instruments, USA). Fourier transform infrared (FT-IR) spectra (4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were recorded with an IR Tracer-100 spectrometer (Shimadzu Co., Ltd, Japan) using the KBr pellet technique. The transmission electron microscope (TEM) images were acquired by an HT-7800 transmission electron microscope (Hitachi Co., Ltd., Japan), and the X-ray photoelectron spectroscopy (XPS) measurements were conducted using an AXIS Ultra DLD X-ray photoelectron spectrophotometer (Shimadzu Co., Ltd., Japan).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePreparation of Y-CD\u003c/h3\u003e\n\u003cp\u003eThe Y-CD was synthesized according to the previous methods with some modifications [\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Briefly, 0.1 g \u003cem\u003eo\u003c/em\u003e-PD and 0.2 g thiourea were mixed in 20 mL of ethanol and stirred for 30 min; the mixture was moved to a 50 mL autoclave, heated at 180 oC for 8 h. The product was dialyzed using a dialysis bag (molecular cut off is 10000) for 8 h to remove the unreacted small molecules. The solutions left in the dialysis bag were further centrifuged at 10000 rounds per minute (rpm) for 10 min to remove the potentially large aggregates, the supernatants were transferred to a glass bottle, and stored at 4 \u003csup\u003eo\u003c/sup\u003eC. Other CDs were synthesized by a similar protocol by changing \u003cem\u003eo\u003c/em\u003e-PD to \u003cem\u003ep\u003c/em\u003e-PD or \u003cem\u003em\u003c/em\u003e-PD in the presence or absence of thiourea.\u003c/p\u003e\n\u003ch3\u003eMeasurements of As in aqueous solutions\u003c/h3\u003e\n\u003cp\u003e100 \u0026micro;L Y-CD was mixed with different concentrations of As\u003csup\u003e3+\u003c/sup\u003e, after reacting for 1 min, the UV-visible absorption spectra were recorded with the wavelength from 300 to 600 nm, and fluorescent spectra were also recorded with the emission wavelength between 450 and 750 nm and the excitation wavelength at 433 nm.\u003c/p\u003e\n\u003ch3\u003eMeasurements of As using smartphone-assisted method\u003c/h3\u003e\n\u003cp\u003eThe round filter paper disk with a diameter of 8 mm was obtained using a handheld puncher (Kamei Co., Yiwu, China), then the paper disks were immersed in the Y-CD solution for 2 min, and taken out to dry in the air. Next, 15 \u0026micro;L solutions with different concentrations of As\u003csup\u003e3+\u003c/sup\u003e were dropped onto the paper disk. After the paper disk dried naturally, photos of the disks were acquired under daylight and under ultraviolet light (365 nm). The green channel signal values of aqueous solution and paper disk photos were acquired using Adobe Photoshop software (Version 7.0.1).\u003c/p\u003e\n\u003ch3\u003eMeasurements of As in oyster samples\u003c/h3\u003e\n\u003cp\u003eThe oyster was purchased from a local supermarket (Yantai, China), and the oyster meat was carefully removed using a cereal knife and treated using conventional acid-assisted digestion [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Briefly, 5 g fresh oyster meat was dried at 105 \u003csup\u003eo\u003c/sup\u003eC until the weight was not changed, then this product was ground to powder, and added into 5 mL HNO\u003csub\u003e3\u003c/sub\u003e and 0.5 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (30% w/w) in an autoclave, heated at 180 \u003csup\u003eo\u003c/sup\u003eC for 5 h, after removing the lid of autoclave, the solutions were heated at 100 \u003csup\u003eo\u003c/sup\u003eC to remove the acid completely, the product was further dissolved in 1 mL water, centrifuged at 13000 rpm for 5 min to remove the potential large precipitate, the supernatant was carefully transferred to a glass bottle and stored at 4 \u003csup\u003eo\u003c/sup\u003eC. The As\u003csup\u003e3+\u003c/sup\u003e was detected using the standard additional method by adding different amounts of the As\u003csup\u003e3+\u003c/sup\u003e standard solution into the pretreated actual samples.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMeasurements of As\u003csup\u003e3+\u003c/sup\u003e in breast cancer cells\u003c/h2\u003e \u003cp\u003e4T1 mouse breast cancer cells were grown with fresh Dulbecco\u0026rsquo;s Modified Eagle\u0026rsquo;s medium (DMEM), supplemented with 10% fetal bovine serum in a humidified 5% CO\u003csub\u003e2\u003c/sub\u003e incubator at 37 \u003csup\u003eo\u003c/sup\u003eC. After the cells were cultured with different concentrations of Y-CD for 8 h, the cell viability was measured using a cell counting kit-8 (Beyotime Biotechnology Co., Hangzhou, China) following the manufacturer\u0026rsquo;s instructions. After the 4T1 cells were incubated with different concentrations of As\u003csup\u003e3+\u003c/sup\u003e for 2 h, 1 mg/mL Y-CD was added and incubated with the cells for another 2 h. After the cells were washed with PBS 3 times, they were treated with 2.5% (v/v) glutaraldehyde (Yuanye Biotechnology Co., Shanghai, China) for 10 min, and DAPI (4\u0026rsquo;,6-diamidino-2\u0026rsquo;-phenylindole) cell staining solution (Beyotime Biotechnology Co., Hangzhou, China) for another 10 min to stain the cell nucleus. After washing the cells using PBS 3 times, the fluorescent images of 4T1 cells were acquired using a Yokogawa CSU-W1 spinning disk field scanning confocal system (Nikon Instruments Inc.).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization of fluorescent Y-CD\u003c/h2\u003e \u003cp\u003eY-CD was prepared through the carbonization process using an \u003cem\u003eo\u003c/em\u003e-PD and thiourea as precursors; the overall synthetic procedure of the Y-CD and the As\u003csup\u003e3+\u003c/sup\u003e detection process is shown in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The characterization results of our prepared Y-CD were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The TEM image in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea indicated that small-sized sphere nanoparticles with a diameter of \u0026sim;10 nm were prepared. The surface functional groups on the Y-CD were measured by FT-IR analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), the broad peak at 3100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicated the presence of hydroxyl and amine functional groups, the peak at 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e represents C\u0026thinsp;=\u0026thinsp;O of the amide/N-H groups, and the peak around 1000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e C-H represents in-plane bending vibration of the benzene ring which comes from the \u003cem\u003eo\u003c/em\u003e-PD (marked with blue strip). The strong peaks at 1450 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 750 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e originated from the stretch vibration and in-plane deformation vibration of C\u0026thinsp;=\u0026thinsp;S coupled with N-H bending in a hydrogen-bonded structure (marked with a yellow strip), the functional groups containing carbon and sulfur originated from polymerization followed by carbonization of \u003cem\u003eo\u003c/em\u003e-PD and thiourea [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Meanwhile, the successful incorporation of S and N atoms into the carbon-rich Y-CD was confirmed by the XPS measurement (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec-f), wide-scan XPS spectrum shows peaks at 162, 287, 400, and 532 eV, which correspond to S2p, C1s, N1s and O1s, respectively [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. These results indicated that the N/S co-doped CD was successfully prepared.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe spectroscopic measurement results of Y-CD were shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg and h, the Y-CD had a strong absorption between 300\u0026ndash;600 nm with a maximum absorbance at about 420 nm and a strong fluorescence between 450\u0026ndash;750 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg). Especially, the maximum fluorescence emission wavelength was not affected by changing the excitation wavelength (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh), which was different from many blue-emission CDs [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], in which the maximum emission wavelengths were red-shifted by increasing the excitation wavelength; therefore, it was beneficial for the application of Y-CD if considering the instrument differences in different laboratories.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eThe feasibility experiments\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ei, the Y-CD was yellow in color under daylight, and emitted red fluorescence (λ\u003csub\u003eem\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;575 nm) under the excitation wavelength of 433 nm (the Stokes shift of the wavelength is 142 nm). To demonstrate that the Y-CD could be used for As\u003csup\u003e3+\u003c/sup\u003e detection, the As\u003csup\u003e3+\u003c/sup\u003e standard solution was mixed with the Y-CD, and the color of Y-CD changed from pale-yellow to deep yellow, and the maximum absorbance wavelength was also red-shifted, accompanied by an increase in absorbance. On the contrary, after the addition of As\u003csup\u003e3+\u003c/sup\u003e into Y-CD solution, the fluorescence spectra of Y-CD solutions decreased significantly along with the maximum emission wavelength undergoing a slight blue shift, and the fluorescence images of Y-CD also changed from luminous yellow to dark yellow under UV light (365 nm). These results indicated the Y-CD could be used for As\u003csup\u003e3+\u003c/sup\u003e detection through colorimetric and fluorescent methods.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eThe mechanism of As\u003csup\u003e3+\u003c/sup\u003e detection\u003c/h2\u003e \u003cp\u003eTo explore the detection mechanism of Y-CD for As\u003csup\u003e3+\u003c/sup\u003e, different CDs were prepared using \u003cem\u003eo\u003c/em\u003e-PD, \u003cem\u003em\u003c/em\u003e-PD, \u003cem\u003ep\u003c/em\u003e-PD and thiourea as the precursor through similar synthetic procedures. As shown in Figs. S1a-c, only \u003cem\u003eo\u003c/em\u003e-PD yielded a distinct UV-Vis absorption peak, whereas \u003cem\u003em\u003c/em\u003e-PD produced broad UV absorption without a defined peak, suggesting irregular morphology of the nanoparticle [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The \u003cem\u003ep\u003c/em\u003e-PD system showed a broad absorption peak between 400 and 500 nm, indicating a heterogeneous particle size detrimental to the colorimetric assay. Co-doping with sulfur (\u003cem\u003evia\u003c/em\u003e thiourea) significantly enhanced the absorption of Y-CDs by forming localized energy transfer centers, confirming that S doping can alter the internal energy level of the material, and facilitating electron transfer [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUpon the addition of As\u003csup\u003e3+\u003c/sup\u003e, S-doped \u003cem\u003eo\u003c/em\u003e-PD CDs exhibited a pronounced redshift (\u0026sim;26 nm) versus non-doped \u003cem\u003eo\u003c/em\u003e-PD CDs (\u0026sim;8 nm). This enhanced spectral shift was attributed to S-doping increasing the binding affinity for As\u003csup\u003e3+\u003c/sup\u003e due to the high affinity of the S atom for As\u003csup\u003e3+\u003c/sup\u003e [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], reducing electron migration energy levels via a stronger static quenching process [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In contrast, the \u003cem\u003em\u003c/em\u003e-PD derived CDs showed no significant spectral changes even with thiourea co-precursor. This might be due to the substantial intramolecular distance between amino groups of \u003cem\u003em\u003c/em\u003e-PD impeding effective complex formation with As\u0026sup3;⁺ [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Meanwhile, \u003cem\u003ep\u003c/em\u003e-PD systems exhibited modest spectral variation upon As\u0026sup3;⁺ addition, but S co-doping induced an observable redshift of spectra accompanied by the emergence of novel absorption features (\u0026sim;525 nm). This phenomenon indicates that amino groups from adjacent \u003cem\u003ep\u003c/em\u003e-PD molecules undergo head-to-head intermolecular interactions with As\u0026sup3;⁺, alongside the S doping incorporated from thiourea, forming durable N-(S-)As\u003csup\u003e3+\u003c/sup\u003e-N complexes [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These results collectively demonstrate S incorporation is crucial for optimizing As\u0026sup3;⁺ detection performance. Furthermore, the spatial arrangement of amino groups in the carbon dots significantly modulates binding affinity and complex stability, thereby influencing the overall detection efficiency [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe fluorescence properties of CDs derived from different precursors were also systematically analyzed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, o-PD based CDs exhibited a fluorescence emission peak at \u0026sim;575 nm, while the peak position remained unchanged with S co-doping. The fluorescence intensity increased by approximately 1.7-fold, supporting the formation of intramolecular fluorophores upon thiourea addition, therefore enhancing As\u003csup\u003e3+\u003c/sup\u003e detection. In contrast, as shown in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ed, \u003cem\u003em\u003c/em\u003e-PD based CDs showed a weaker fluorescence emission with the peak at 500 nm. Notably, the fluorescence intensity was significantly enhanced when \u003cem\u003em\u003c/em\u003e-PD and thiourea were employed as co-precursors, which is consistent with the previously observed enhancing effect of S co-doping on fluorescence signals [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, \u003cem\u003ep\u003c/em\u003e-PD-derived CDs showed no significant fluorescence emission regardless of S co-doping using thiourea as co-precursor, which was due to the irregular morphology of CDs and the pronounced internal filter effect contributing to fluorescence quenching.\u003c/p\u003e \u003cp\u003eThe hydrodynamic size and zeta potential of Y-CD were also measured to further study the interaction of Y-CD with As\u003csup\u003e3+\u003c/sup\u003e, which were 4.86 nm and \u0026minus;\u0026thinsp;56.2 mV, respectively. After the addition of As\u003csup\u003e3+\u003c/sup\u003e, the hydrodynamic size and zeta potential of Y-CD-As\u003csup\u003e3+\u003c/sup\u003e were increased to 209.57 nm and 10.50 mV, further confirmed the binding between the amino groups and sulfur atoms with As\u003csup\u003e3+\u003c/sup\u003e, this binding induced the aggregation of Y-CD and also altered the surface charge of the materials to a positive value due to the presence of positively charged As\u003csup\u003e3+\u003c/sup\u003e, which was consistent with the previous reports that dithiothreitol [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] or thiodiacetic acid [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] conjugated nanoparticles have high affinity with As\u003csup\u003e3+\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eOur experimental findings demonstrated that Y-CD can effectively interact with As\u003csup\u003e3+\u003c/sup\u003e via the reaction between amino groups and sulfur atoms, which leads to static quenching, resulting in a reduction of electron transition energy and a redshift of the maximum absorption wavelength with increased absorbance. Additionally, during the electron transition between the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), the interaction between electrons and the positively charged As\u003csup\u003e3+\u003c/sup\u003e promotes an energy relaxation process, which leads to the deactivation of the excited state, ultimately quenching the fluorescence signals. These results are consistent with previous literature reports [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eThe optimization experiments\u003c/h2\u003e \u003cp\u003eTo improve the detection performance of the method, different experimental conditions were optimized. As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, the fluorescent spectra of Y-CD were measured in solutions of different pH in the absence and presence of As\u003csup\u003e3+\u003c/sup\u003e; the fluorescence signals of solutions decreased slowly as the pH decreased from 10 to 4, regardless of whether there was As\u003csup\u003e3+\u003c/sup\u003e or not; however, at pH 5, the fluorescence spectra decreased significantly in the presence of As\u003csup\u003e3+\u003c/sup\u003e. Similarly, the absorbance spectra of solutions were also red-shifted as the pH decreased, and the spectral difference reached a maximum at pH 5 (Fig. S2a). To conveniently evaluate the effect of pH on the detection of As\u003csup\u003e3+\u003c/sup\u003e, the maximum fluorescence intensity of fluorescent spectra and the absorbance ratio of absorption spectra at 416 nm and 452 nm (A416nm/A452nm) were used, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and S2b, the most significant differences between the two solutions in the absence and presence of As\u003csup\u003e3+\u003c/sup\u003e were observed at pH 5. The low fluorescent intensity of Y-CD alone in acidic solution was ascribed to the interaction of the surface-attached functional groups with H\u003csup\u003e+\u003c/sup\u003e ions and might induce the destruction of fluorescence generating units of Y-CD, which is consistent with previous reports [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Since the As\u003csup\u003e3+\u003c/sup\u003e could interact with Y-CD and induce a change in its dispersion state, the Y-CD concentration was also optimized to increase the alterations in absorption and fluorescent signals, therefore improving the detection sensitivity of As\u003csup\u003e3+\u003c/sup\u003e. As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec-d and S2c-d, the spectra changed more significantly with increasing the Y-CD concentration from 0.15 mg/mL to 4.8 mg/mL, while they became less obvious if the Y-CD concentration was more than 0.6 mg/mL. It was interesting to find that even after mixing As\u003csup\u003e3+\u003c/sup\u003e with Y-CD for 0.5 min, the spectra were quickly changed and kept at a stable state from 0.5 min to 18.5 min (see Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee-f and S2e-f). Therefore, in the following experiment, the pH of the solution was selected as 5, the concentration of Y-CD was 0.6 mg/mL, and the reaction time between Y-CD and As\u003csup\u003e3+\u003c/sup\u003e was determined as 5 min to facilitate the experimental operation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eDetection of As\u003csup\u003e3+\u003c/sup\u003e in aqueous solution\u003c/h2\u003e \u003cp\u003eTo verify the ability of the Y-CD-based detection method for As\u003csup\u003e3+\u003c/sup\u003e detection, different concentrations of As\u003csup\u003e3+\u003c/sup\u003e were added to Y-CD solutions. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, the fluorescence of Y-CD decreased gradually with increasing the concentration of As\u003csup\u003e3+\u003c/sup\u003e from 1 \u0026micro;M to 25 \u0026micro;M, and remained at a very low level if more than 25 \u0026micro;M As\u003csup\u003e3+\u003c/sup\u003e was added. The fluorescence images of Y-CD interact with different concentrations of As\u003csup\u003e3+\u003c/sup\u003e also showed a decrease in intensity (The samples were irradiated using a single wavelength LED light at 465 nm). The fluorescence intensities of Y-CDs at 575 nm had a linear response toward the logarithm of the concentration of As\u003csup\u003e3+\u003c/sup\u003e ([As\u003csup\u003e3+\u003c/sup\u003e]) from 2.5 \u0026micro;M to 25 \u0026micro;M (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), while the regression equation can be expressed as F\u0026thinsp;=\u0026thinsp;63141\u0026ndash;42243 log [As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M) (r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.988), and the limit of detection and limit of quantification were estimated as 1 \u0026micro;M and 3.3 \u0026micro;M, respectively (S/N\u0026thinsp;=\u0026thinsp;3).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSimilarly, the absorption spectra of Y-CD in the presence of As\u003csup\u003e3+\u003c/sup\u003e were also measured, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, the yellow color of Y-CD solution was enhanced and the absorption spectra were gradually red-shifted with increasing the amounts of As\u003csup\u003e3+\u003c/sup\u003e from 2.5 \u0026micro;M to 25 \u0026micro;M, the absorbance ratios of Y-CDs at 416 nm and 452 nm (A416nm/A452nm) were also decreased gradually between 2.5 \u0026micro;M to 25 \u0026micro;M (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed), the regression equation can be expressed as A416nm/A452nm\u0026thinsp;=\u0026thinsp;1.632\u0026ndash;0.704 log [As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M) (r\u003csup\u003e2\u003c/sup\u003e= 0.984), and the limit of detection and limit of quantification were estimated to 1 \u0026micro;M and 3.3 \u0026micro;M, respectively (S/N\u0026thinsp;=\u0026thinsp;3).\u003c/p\u003e \u003cp\u003eThis method has advantages like being easier to conduct, cost and time efficiency. According to the national food safety standard for As\u003csup\u003e3+\u003c/sup\u003e element, the MAC of As\u003csup\u003e3+\u003c/sup\u003e was 6.7 \u0026micro;M in fish and seafood; therefore, our method could be used for easily determining the safety of food.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSelectivity experiment\u003c/h2\u003e \u003cp\u003eThe selectivity of this method was also evaluated by adding different kinds of interferences, including metal ions, proteins, peptides, amino acids, and carbohydrates, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee-f, the common proteins, peptides, amino acids, carbohydrates, sodium ascorbate, dopamine, and many metal ions (Ca\u003csup\u003e2+\u003c/sup\u003e, Ni\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, Hg\u003csup\u003e2+\u003c/sup\u003e, Pb\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+,\u003c/sup\u003e and Mg\u003csup\u003e2+\u003c/sup\u003e) had a negligible impact on the Y-CD spectra. We also observed that the Fe\u003csup\u003e2+\u003c/sup\u003e and Fe\u003csup\u003e3+\u003c/sup\u003e induced the fluorescence intensity of Y-CD to decrease, Fe\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e induced the absorption spectra red-shifted to some extent (see Fig. S3). This phenomenon might be induced by the coordination of metal ions with Y-CD, resulting in a change in the dispersion state of Y-CD. To eliminate the interference of Fe\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e on the As\u003csup\u003e3+\u003c/sup\u003e detection, EDTA was used as the masking agent in this system, as shown in Fig. S4. With the addition of EDTA, the impacts of Fe\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e on the Y-CD spectra were eliminated. Due to the very weak bonding capacity of EDTA with As\u003csup\u003e3+\u003c/sup\u003e, the spectra of Y-CD were not changed regardless of whether EDTA was added along with As\u003csup\u003e3+\u003c/sup\u003e or not. In general, we might demonstrate that our method had reasonable selectivity for As\u003csup\u003e3+\u003c/sup\u003e detection.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eDetection of As\u003csup\u003e3+\u003c/sup\u003e using smartphone-assisted method\u003c/h2\u003e \u003cp\u003eTo simplify the As\u003csup\u003e3+\u003c/sup\u003e detection process, different concentrations of As\u003csup\u003e3+\u003c/sup\u003e were added into Y-CD solutions or Y-CD contained filter paper disk, and the photos of solutions were acquired under daylight or ultraviolet light using a smartphone. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, with increasing the concentrations of As\u003csup\u003e3+\u003c/sup\u003e, the color of the solutions/paper disks changed from yellow to brown, while their fluorescent intensities were also decreased, which can be observed by the naked eye; this phenomenon was consistent with the above-mentioned experiment results. To quantitatively determine the amounts of As\u003csup\u003e3+\u003c/sup\u003e, the green channel signal intensities of each photo were extracted using Photoshop software, the signal intensity decreased with increasing the concentrations of As\u003csup\u003e3+\u003c/sup\u003e from 2 \u0026micro;M to 20 \u0026micro;M, and the linear regression equations are I\u0026thinsp;=\u0026thinsp;226.63\u0026ndash;105.24 log[As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M), (r\u003csup\u003e2\u003c/sup\u003e= 0.982) for As\u003csup\u003e3+\u003c/sup\u003e detection in solutions (color change measurement), I\u0026thinsp;=\u0026thinsp;292.63\u0026ndash;142.24 log[As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M), (r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.992) for As\u003csup\u003e3+\u003c/sup\u003e detection in solutions (fluorescence change measurement), I\u0026thinsp;=\u0026thinsp;139.25\u0026ndash;55.86 log[As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M), (r\u003csup\u003e2\u003c/sup\u003e= 0.996) for As\u003csup\u003e3+\u003c/sup\u003e detection on paper strip disks (color change measurement), and I\u0026thinsp;=\u0026thinsp;251.74\u0026ndash;116.46 log[As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M), (r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.992) for As\u003csup\u003e3+\u003c/sup\u003e detection on paper strip disks (fluorescence change measurement). By this means, we have developed a more convenient and cost-efficient method for As\u003csup\u003e3+\u003c/sup\u003e determination with comparable detection capabilities.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eDetection of As\u003csup\u003e3+\u003c/sup\u003e in the actual sample\u003c/h2\u003e \u003cp\u003eTo demonstrate the application of this method for actual sample detection, high-temperature acid digestion methods were used to pretreat three kinds of oysters, then different amounts of As\u003csup\u003e3+\u003c/sup\u003e were added based on the standard addition method. As shown in Figs. S5a-b, the fluorescence intensity of Y-CD decreased with increasing concentrations of As\u003csup\u003e3+\u003c/sup\u003e in the oyster samples, the regression function for As\u003csup\u003e3+\u003c/sup\u003e detection was F\u0026thinsp;=\u0026thinsp;62712\u0026ndash;2595 [As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M), (r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.999). A similar phenomenon was also observed by measuring the absorption spectra of solutions, as shown in Figs. S5c-d, the absorbance spectra were red-shifted with the addition of As\u003csup\u003e3+\u003c/sup\u003e in the oyster samples, and the regression function for As\u003csup\u003e3+\u003c/sup\u003e detection was A416nm/A452nm\u0026thinsp;=\u0026thinsp;1.156\u0026ndash;0.0149 [As\u003csup\u003e3+\u003c/sup\u003e] (\u0026micro;M), (r\u003csup\u003e2\u003c/sup\u003e= 0.999).\u003c/p\u003e \u003cp\u003eFurthermore, 0, 6, and 15 \u0026micro;M As\u003csup\u003e3+\u003c/sup\u003e were added into 3 kinds of oysters to examine the performance of our dual-mode detection method, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the recoveries of our proposed method were between 95% to 112%. It should be noted that a naked-eye distinguishable color or fluorescence was observed if the As\u003csup\u003e3+\u003c/sup\u003e exceeded the MAC (data not shown). In addition, the samples were also detected using the ICP-MS method, and a good correlation among the colorimetric method, fluorescent method, and ICP-MS was obtained. Hence, our method not only shortened the detection time and simplified the whole operating process, but also provided a dual-mode method for As\u003csup\u003e3+\u003c/sup\u003e detection in actual samples.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAnalyses of As\u003csup\u003e3+\u003c/sup\u003e in oyster samples (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD, \u0026micro;mol kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of wet weight).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecies\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eAdd (\u0026micro;M)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c7\" namest=\"c3\"\u003e \u003cp\u003eMethod comparison\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eICP-MS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c7\" namest=\"c4\"\u003e \u003cp\u003eThis method\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUV-Vis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRecovery (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eFluorescence\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRecovery (%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSample 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.02\u0026plusmn;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.01\u0026plusmn;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.5\u0026plusmn;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e108\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5.8\u0026plusmn;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.8\u0026plusmn;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e15.5\u0026plusmn;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e103\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSample 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.05\u0026plusmn;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.04\u0026plusmn;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.8\u0026plusmn;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.7\u0026plusmn;0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e112\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.7\u0026plusmn;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e15.7\u0026plusmn;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e105\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSample 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.04\u0026plusmn;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.02\u0026plusmn;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eN/D\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.4\u0026plusmn;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5.7\u0026plusmn;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.5\u0026plusmn;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e15.3\u0026plusmn;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e102\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eDetection of As\u003csup\u003e3+\u003c/sup\u003e in cancer cells\u003c/h2\u003e \u003cp\u003eTo further investigate the application of Y-CD for As\u003csup\u003e3+\u003c/sup\u003e detection in living cells, different concentrations of Y-CD were first incubated with 4T1 breast cancer cells, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, cell viability remained above 80% with Y-CD concentrations up to 3.5 mg/mL. After the 4T1 cells were incubated with different concentrations of As\u003csup\u003e3+\u003c/sup\u003e, they were further stained with Y-CD. The fluorescent signal intensity of Y-CD decreased with the concentration of As\u003csup\u003e3+\u003c/sup\u003e increased from 0 \u0026micro;M to 30 \u0026micro;M, there was also no fluorescent signal in the absence of Y-CD. The overall experiment result indicated that Y-CD could serve as a good candidate for As\u003csup\u003e3+\u003c/sup\u003e detection in the living cell system, which is meaningful for human health risk assessment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, a dual-mode method was developed for As\u003csup\u003e3+\u003c/sup\u003e detection by investigating the fluorescence and color changes of Y-CD in the presence of As\u003csup\u003e3+\u003c/sup\u003e. The Y-CD probe was synthesized conveniently by employing \u003cem\u003eo\u003c/em\u003e-PD and thiourea as the precursor. The amino and sulfur atoms could coordinate with As\u003csup\u003e3+\u003c/sup\u003e, which resulted in the dispersion state changes of Y-CD, and further resulted in the red-shift of absorption spectra and decrease of fluorescence intensity of Y-CD. As low as 1 \u0026micro;M As\u003csup\u003e3+\u003c/sup\u003e could be detected without a sophisticated instrument in less than 5 min. Especially, our method could be used for As\u003csup\u003e3+\u003c/sup\u003e detection in aquatic products and cancer cells, which is meaningful for food safety measurement and human health risk assessment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe online version contains supplementary material available at https://doi.org/.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by the Natural Science Foundation of Shandong Province (ZR2023MC178) and the Youth Innovation Technology Project of Higher School in Shandong Province (Food Nanotechnology Innovation Team).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eShuyang Sun: methodology, writing—review and editing. Yu Gao: formal analysis, software. Daohong Zhang: conceptualization. Lihong Su: investigation. Chengke Wang: supervision, writing—review and editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWang C, Sun S, Wang P, Zhao H, Li W (2024) Nanotechnology-based analytical techniques for the detection of contaminants in aquatic products. Talanta 269:125462.\u003c/li\u003e\n\u003cli\u003eGhosh D, Ghosh A, Bhadury P (2022) Arsenic through aquatic trophic levels: effects, transformations and biomagnification\u0026mdash;a concise review. Geosci Lett 9:20.\u003c/li\u003e\n\u003cli\u003eRajendran S, Ramanaiah D. V, Kundu S, Bhunia S. 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Angew Chem Int Ed 54:5360\u0026ndash;5363.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"carbon dots, As3+, colorimetric, fluorescence, Oyster, Smartphone-assisted detection","lastPublishedDoi":"10.21203/rs.3.rs-9144608/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9144608/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eArsenic (As\u003csup\u003e3+\u003c/sup\u003e) contamination in food and biological systems is harmful to human health; therefore, it is urgent to develop a sensitive and rapid method for As\u003csup\u003e3+\u003c/sup\u003e detection. Herein, a fluorescence and colorimetric dual-mode sensing approach was developed using a nitrogen and sulfur co-doped yellow emissive carbon dots (Y-CD). The coordination of amino and sulfur groups in Y-CD with As\u003csup\u003e3+\u003c/sup\u003e leads to changes of the Y-CD dispersion state, which induces a significant red shift in the absorption spectra and a decrease in fluorescence intensities. A smartphone-assisted detection approach was employed for eliminating the need of sophisticated equipment. The proposed method exhibited a low detection limit of 1 mM As\u003csup\u003e3+\u003c/sup\u003e, rapid response within 5 minutes, and was applied for As\u003csup\u003e3+\u003c/sup\u003e detection in both oysters and living cells, demonstrating its robustness in complex matrices.\u003c/p\u003e","manuscriptTitle":"Colorimetric and fluorescent dual-mode detection of arsenic in oysters and living cells using N/S doped carbon dots","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-27 17:29:50","doi":"10.21203/rs.3.rs-9144608/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"df0ad413-340e-4224-bb95-4aa41aefb525","owner":[],"postedDate":"March 27th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Rejected","date":"2026-04-29T20:26:57+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-29T20:39:15+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-27 17:29:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9144608","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9144608","identity":"rs-9144608","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}