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Fluorescent sensor for selective determination of copper ion based on N-acetyl-Lcysteine capped CdHgSe quantum dots Qingqing Wang, Xiangyang Yu, Guoqing Zhan, Chunya Li

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Biosensors and Bioelectronics

Received date: 23 October 2013 Accepted date: 4 November 2013 Cite this article as: Qingqing Wang, Xiangyang Yu, Guoqing Zhan, Chunya Li, Fluorescent sensor for selective determination of copper ion based on Nacetyl-L-cysteine capped CdHgSe quantum dots, Biosensors and Bioelectronics, http://dx.doi.org/10.1016/j.bios.2013.11.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Fluorescent sensor for selective determination of copper ion based on N-acetyl-L-cysteine capped CdHgSe quantum dots Qingqing Wang, Xiangyang Yu, Guoqing Zhan, Chunya Li* Key Laboratory of Analytical Chemistry of the State Ethnic Affairs Commission, College of Chemistry and Materials Science, South- Central University for Nationalities, Wuhan 430074

Abstract Using N-acetyl-L-cysteine as a stabilizer, well water-dispersed, high-quality and stable CdHgSe quantum dots were facilely synthesized via a simple aqueous phase method. The as-prepared N-acetyl-L-cysteine capped CdHgSe quantum dots were thoroughly characterized by transmission electron microscopy, X-ray diffraction spectroscopy and FTIR. A fluorescent sensor for selective determination of copper ions was developed using N-acetyl-L-cysteine capped CdHgSe quantum dots as fluorescent probe. The fluorescence intensity of N-acetyl-L-cysteine capped CdHgSe quantum dots decreased when interacted with copper ions due to the formation of coordination complex and aggregates. The method possesses high selectivity, and is not influenced by some potential interferences such as Ag+, Zn2+, Co2+and Ni2+ etc. Under the optimal conditions, the change of fluorescence intensity (ΔI) was linearly proportional to the concentration of copper ions in the range of 1.0 × 10-9 mol L-1 ~ 4.0 × 10-7 mol L-1, with a detection limit as low as 2.0 × -1

10-10 mol L (S/N=3). The developed method had been successfully employed to determine Cu2+ in shrimp and South-lake water samples, and the results were verified by atomic absorption spectroscopy. The fluorescent sensor was demonstrated to be selective, sensitive and simple for copper ion determination, and promise for practical applications. Keywords: N-acetyl-L-cysteine, CdHgSe, Quantum dots, Copper ion, Sensor.

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* Corresponding authors. E-mail: [email protected]

1. Introduction Metal ions with well-balanced concentration are of benefit to the ecosystem and human health. Unfortunately, they will be very hazardous at an abnormal concentration. Therefore, simple, selective and sensitive methods for the determination of metal ions have been attracted considerable attention (Xiang et al., 2009). As an essential trace element, copper ions play important roles in a variety of fundamental biological processes in organism, and occupy an important position in environmental and biological systems (Alies et al., 2012; Li et al., 2013; You et al., 2011). Nevertheless, copper ion at excessive concentration is very toxic and usually leads to liver damage especially for infants (Zietz et al., 2003). It has proven to be related with neurodegenerative diseases (Bruijn et al., 2004; Tiffany-Castiglioni et al., 2011; Waggoner et al., 1999), such as Alzheimer’s, Parkinson’s and familial amyotropic lateral sclerosis, and is also suspected to cause amyloid precipitation and toxicity. Hence, to monitor and to regulate the concentration of copper ion is essential for organisms. Many techniques including atomic absorption spectroscopy (Lin et al., 2001) and plasma mass spectroscopy (Becker et al., 2007) have been developed for copper ion determination. Although those methods are generally good sensitivity and precision, only coupled with HPLC, free Cu2+ in the complex can be detected by ICP-MS. Instruments for atomic spectroscopic techniques tend to be complex, expensive and time-consuming. Compared with these methods, the fluorescence spectroscopy is frequently used to analysis copper ions due to the fascinating properties of quantum dots (QDs), and is proven to be more feasible, sensitive and

2

simple. Using luminescent semiconductor quantum dots as probes, copper ions in aqueous samples were successfully determined (Chen et al., 2002). Liu’s group utilized CdTe/CdS QDs coupled with glyphosate for selective measurement of copper ions (Liu et al., 2012). Methods which use QDs as probes for the determination of copper ion possess low detection limit (Chen S. et al., 2011; Liu et al., 2012). However, they are often subjected to the interference of some metal ions, such as Fe3+ (Chen et al., 2002; Fernández-Argüelles et al., 2005) and Ag+ (Gattás-Asfura et al., 2003) etc. Ternary cadmium-mercury chalcogenides are of especial interest, since they could be applied in electroluminescence devices, biological field (Rogach et al., 2007) and so on. Stabilizer occupies an important role in synthesis process of ternary quantum dots. CdHgTe

composite

nanocrystals

have

been

prepared

applying

1-mercapto-2,3-propanediol as stabilizer (Harrison et al., 2000). In addition, captopropionic acid (MPA) is also often chosen as stabilizer in synthesis process. But it is noteworthy that these organic stabilizers are volatile with an awful odor and some of them are carcinogenic. N-Acetyl-L-cysteine (NAC) is an antioxidant and is known to protect cells against oxidative stress and QDs-induced cytotoxicity (Choi et al., 2007; Lovrić et al., 2005). In addition, as a derivative from L-cysteine, NAC has excellent biocompatibility, good water solubility and is low cost, stable, nonvolatile, and odorless (Boman et al., 1983; Choi et al., 2007; James et al., 2003; Lovrić et al., 2005; Prescott et al., 1979; Särnstrand et al., 1995). Until now, no direct application of NAC as a stabilizer in the synthesis of ligand-protected CdHgSe QDs in aqueous

3

solution. In this work, we reported an inexpensive and facile synthetic route to fabricate CdHgSe QDs using NAC as stabilizer. The as-prepared QDs possess excellent water-solubility, stability, and higher quantum yield (QY) of 40% than near infrared (NIR) CdHgTe and CdHgTe⁄CdS quantum dots with quantum yield of about 12% and 15% (Chen H. et al., 2011). When interacted with Cu2+, a coordination reaction occurred between the NAC on the surface of the CdHgSe QDs and copper ions to form a coordination compound, as illustrated in Fig. S 1, and thus leads to the decrease of the fluorescence intensity of NAC capped CdHgSe QDs. Based on the fluorescence intensity change (ΔI), which is the difference between the original fluorescence intensity (F0) of the NAC capped CdHgSe QDs and the actual fluorescence intensity (F) after being reacted with Cu2+, a sensitive and selective fluorescent sensor was developed for copper ions. Copper ions in shrimp and South-lake water samples were successfully assayed with the mentioned method. 2. Experimental 2.1 Materials NAC was purchased from Shanghai Aladdin Reagent Inc. (Shanghai, China). CuCl2.2H2O was bought from Shanghai Reagent Factory Four (Shanghai, China). Selenium powder and NaBH4 were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). CdCl2·2.5H2O was purchased from Chengdu Chemical Reagent Plant (Chengdu, China). All water used in the experiment was ultrapure water.

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2.2 Apparatus All fluorescence spectra of the NAC capped CdHgSe QDs were measured using a Perkin Elmer LS-55 luminescence spectrometer. The excitation wavelength (λex) at 390 nm was selected for all experiments. All pH values were measured with pHS-3 meter (Shanghai, China). A Tecnai G2 20-Transmission electron microscopy operating at 200 KV was used for morphology characterization. X-ray diffraction analysis was conducted on a Bruker D8 X-ray diffractometer (Bruker Company, Germany) using the Cu Kα radiation with 40 kV and 50 mA. UV/Vis analysis was performed on PE Labmda Bio 35 (PerkinElmer, USA). FT-IR spectrum was recorded on a Nexus 470 spectrophotometer using KBr pellet. The quantum yield of CdHgSe QDs was measured according to the literature (He et al., 2009; Yang et al., 2003). 2.3 Synthesis of NAC capped CdHgSe QDs Typical procedure for the synthesis of NAC capped CdHgSe QDs was described as following, similar to the previously reported (Wang et al., 2010). NaBH4 reacted with selenium powder at a molar ratio of 2:1 in ultrapure water was used to prepare NaHSe solution. CdCl2 solution (0.04 mmol) and NAC (0.096 mmol) were loaded into a 100 mL three-neck flask, followed by addition of 10 mL of ultrapure water under the protection of N2. The pH value of the reaction mixture was adjusted to ~11.5 by adding sodium hydroxide solution drop-wise. Then 4.00 mL HgCl2 (0.01 molL-1) solution was added slowly drop-wise. After homogeneous mixing, NaHSe solution (84 μL) was added into the reaction mixture using a syringe, and vigorously

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stirred for 4 h at 80ºC. The final composition ratio of n(Cd)/n(Se)/n(NAC) would be calculated to be 1:0.5:2.4. The concentration of NAC capped CdHgSe QDs estimated from NaHSe would be 5.9 × 10-4 molL-1. The obtained NAC capped CdHgSe QDs solution was stored in a refrigerator and proven to be stable at least 4 months. 2.4 Analytical procedure A 1.0 mg mL-1 stock solution of copper chloride was prepared, and was used as standard solution, from which a series of Cu2+ solution can be obtained just by diluted with phosphate buffer solution. NAC capped CdHgSe QDs solution and various amounts of freshly prepared Cu2+ solution were mixed in phosphate buffer solution, and equilibrated for 10 min in dark place before the spectral measurements. Fluorescence emission spectra were recorded at the excitation wavelength of 390 nm. The slit widths for excitation and emission were 7 nm and 15 nm, respectively. The change of fluorescence intensity between NAC capped CdHgSe QDs solution and the mixed solution was used for the determination of Cu2+. 3 Results and discussion 3.1 Characterizations of NAC capped CdHgSe QDs Transmission electron microscopy (TEM) was employed to characterize the morphology of the as-prepared NAC capped CdHgSe QDs. As shown in Fig. 1(a), the TEM image reveals that the shape of the NAC capped CdHgSe QDs was spherical and well proportioned. The average size of the NAC capped CdHgSe QDs estimated from the TEM image is to be 2.09 ± 0.02 nm, which is in good agreement with the value, 2.01 nm, calculated from the X-ray diffraction pattern using the

6

Scherrer-equation. X-ray diffraction (XRD) pattern of the NAC capped CdHgSe QDs is shown in Fig. 1(b). The broadening of the diffraction peaks indicated the small size of the obtained NAC capped CdHgSe QDs. The XRD pattern shows some broad peaks appearing at 2θ = 24.26º, 42.15º and 49.43º. These peaks are due to the diffraction from (111), (220), and (311) planes of cubic CdSe (JCPDS 65-9275). FTIR spectra of NAC (curve I) and the NAC capped CdHgSe QDs (curve II) were displayed in Fig. 1(c). As shown in curve I, the characteristic peak at 2556 cm-1 is corresponding to S-H stretching vibration. The peak located at 1723 cm-1 is attributed to the asymmetric stretching of carboxyl group. Furthermore, peaks located at 2981 cm-1, 2800 cm-1 and 2906 cm-1 are due to C-H stretching vibrations. However, in the case of NAC capped CdHgSe QDs (curve II), the characteristic peak of S-H disappeared, which indicates that the S-H bond was cleaved and a new bond was formed between NAC and CdHgSe QDs. Furthermore, the characteristic absorptions of methyl and methylene, which are corresponding to the peaks located at the wave number of 2989.93, 2931.76 and 2848.85 cm-1, are still observed obviously in curve II. The above results indicate that the NAC has been successfully modified onto the CdHgSe QDs surface. 3.2 Optimization of the experimental conditions 3.2.1 Influences of pH values The fluorescence intensity change (ΔI) is chosen as a criterion to examine the influences of pH values on the sensitivity for Cu2+ determination. 5.9 × 10-5 mol L-1

7

NAC capped CdHgSe QDs solution was used as a fluorescent system to explore the dependence of the fluorescence intensity change before and after being interacted with 1.0 × 10-7 mol L-1 Cu2+ on the solution pH values. As shown in Fig. 2, in the pH values ranged from 6.0 to 9.0, a dramatic increase in ΔI values was found positively related with the solution pH values even though a folding point turns out at pH 8.5. A maximum value for ΔI is obtained at pH 9.0. Further increasing pH values from 9.0 to 12.0, it is evident that the tendency for ΔI is on the decline. Thus, a phosphate buffer solution at pH 9.0 was selected for the further investigations. 3.2.2 Effect of the NAC capped CgHgSe QDs concentration The influence of NAC capped CdHgSe QDs concentration on the fluorescence response of Cu2+ was investigated. When Cu2+ concentration was controlled at 1.0 × 10-7 mol L-1, the change of fluorescence intensity (ΔI) was observed to increase with the NAC capped CdHgSe QDs concentration increasing from 2.3 × 10-5 mol L-1 to 5.9 × 10-5 mol L-1. In this concentration range, Cu2+ exceeds the binding sites that NAC capped CdHgSe QDs can supply for the coordination interaction, leading to the complete quenching of their fluorescence. Thus, a dramatic increasing was observed for ΔI values. With further increasing the NAC capped CdHgSe QDs concentration from 5.9 × 10-5 mol L-1 to 2.3 × 10-4 mol L-1, the binding sites for the coordination reaction will excessively exceed the amount of Cu2+. As a result, the change of fluorescence intensity increased slightly and nearly a steady state will be obtained ultimately. Therefore, we selected 5.9 × 10-5 mol L-1 as the appropriate NAC capped CdHgSe QD concentration.

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3.2.3 Effects of adding sequence of reagents and reaction time The mixing sequence and reaction time also affect the values for ΔI, further affect the sensitivity for Cu2+ determination. It was found that the optimized sequence is the first addition of the NAC capped CdHgSe QDs, then phosphate buffer solution, and the last addition of Cu2+ solution. A maximum value for ΔI was achieved when the NAC capped CdHgSe QDs were interacted with copper ions for 10 min at room temperature. The fluorescence intensity of the reaction system can remain stable at least for 1 h. 3.3 Analytical characteristics Fluorescence spectra of 5.9 × 10-5 mol L-1 NAC capped CdHgSe QDs before and after being interacted with Cu2+ were recorded, and were used to investigate the quenching mechanism. As shown in Fig. 3 A, it was found that the fluorescence intensity of the NAC capped CdHgSe QDs decreased with Cu2+ concentration increasing, indicating Cu2+ has quenching effect on the NAC capped CdHgSe QDs. According to the principle of ligand effect, NAC possesses nitrogen atoms and oxygen atoms bearing lone pair electrons, especially possesses carboxy groups, thus have coordination ability towards Cu2+, and would be an excellent receptor for Cu2+. As the fluorescence intensity of the as-prepared QDs decreased linearly with Cu2+ concentration increasing, thus a method for Cu2+ determination can be developed based on the fluorescence quenching of the NAC capped CdHgSe QDs. The calibration curve for the determination of Cu2+ was presented in Fig. 3 B. Under optimal conditions, the fluorescence intensity (ΔI) was found to be linearly

9

proportional to the Cu2+ concentration (c) in the range from 1.0 × 10-9 mol L-1 to 4.0 × 10-7 mol L-1 with an equation of ΔI = 0.817c (nmolL-1) + 4.66 (R=0.997). The determination limit was estimated to be 2.0 × 10-10 mol L-1 (S/N =3). Compared to the results based on Au and [email protected] nanoclusters for Cu2+ determination, the linear range is relatively narrow (Liu et al., 2011). However, compared with other methods listed in Table S 1, the linear range of the developed sensor is comparable or superior. The detection limit is much lower than that of previously reported (Afkhami et al., 2013; Chen et al., 2013; Li et al., 2011; Zhang et al., 2013;Chen S. et al., 2011; Liu et al., 2012; Koneswaran et al., 2009). The detection limit is far lower than the maximum level ~20 mmol L-1 in the United States, 15 mmol L-1 in Canada and 30 mmol L-1 in the European Union. Therefore, the developed method would be superior sensitivity and possess practical applications in real sample analysis. The quenching mechanism of the NAC capped CdHgSe QDs with Cu2+ was studied by fluorescence and UV–vis absorption spectra. According to previous reports (Chen et al., 2006; Duan et al., 2011), if the fluorescence of QDs was quenched through an electron transfer process between surface ligands and metal ions, the excitation wavelength will not shift. On the other hand, if the fluorescence of QDs was quenched due to the formation of indissolvable precipitate onto the QDs surface, a shift on the excitation spectra will be observed obviously (Isarov et al., 1997; Liu et al., 2012; Pei et al., 2012). As illustrated in Fig. 3A, the fluorescence intensity of the NAC capped CdHgSe QDs was quenched without spectra shift in the presence of Cu2+. As shown in Fig. S2, transmission electron microscopy was also used to examine

10

the interaction between the NAC capped CdHgSe QDs and Cu2+ at the concentration of 2.0 × 10-8 (b), 2.0 × 10-7 (c) and 2.0 × 10-6 (d) molL-1. Seen from Fig. S2 (a), it was found that NAC capped CdHgSe QDs dispersed very well. When being interacted with Cu2+, a partial aggregation of them can be introduced. With the Cu2+ concentration increasing, the aggregation degree increased evidently. It was reasonable to conclude that initial highly dispersed NAC capped CdHgSe QDs is attributable to the stronger electrostatic repulsion between negatively charged QDs. When Cu2+ at relatively high concentration was added, not only negative charges will be partly neutralized but also three-dimensional network will be formed through bridge between NAC capped CdHgSe QDs and Cu2+, thus, leading to the formation of aggregates and causing the decrease of fluorescence intensity of QDs. Therefore, it ought to believe that the fluorescence quenching of the NAC capped CdHgSe QDs by Cu2+ is based on synthetical effects. To further understand the quenching effect, UV–vis absorption spectra of the NAC capped CdHgSe QDs in the absence (a) and presence (c) of Cu2+ ions were also investigated and shown in Fig. 4. No shift was observed on the absorption peak of 5.9 × 10-5 mol L-1 NAC capped CdHgSe QDs with addition of 2.0 × 10-7 molL-1 Cu2+. However, the absorbance of the NAC capped CdHgSe QDs decreased significantly after being interacted with Cu2+. In order to verify the fact that the coordination reaction between the NAC modified on the CdHgSe QDs surface and Cu2+ leads to the change of spectroscopic properties, a competitive binding experiment between EDTA and the NAC capped CdHgSe QDs towards Cu2+ was performed. Viewed from

11

Fig. 4 b, the presence of EDTA resulted in the spectrum reversal of the NAC capped CdHgSe QDs. In other words, the formation of EDTA-Cu2+ complex can make Cu2+ liberate from the complex system using the NAC capped CdHgSe QDs as ligand. The result was also confirmed by the effect of EDTA on the fluorescence spectroscopy of the NAC capped CdHgSe QDs. As shown in Fig. S3, using EDTA as a competitive ligand to interact with Cu2+, the fluorescence intensity of the NAC capped CdHgSe QDs can partially be reversed. The phenomenon indicates that the strong interaction between EDTA and Cu2+ help to keep the NAC capped CdHgSe QDs free from coordination, thus help to maintain its fluorescence intensity, and thus to benefit to verifying the quenching mechanism of fluorescence spectroscopy. 3.4 Selectivity, reproducibility and stability As well known, high specificity is crucial for every analytical method. The selectivity for the determination of Cu2+ based on the NAC capped CdHgSe was thoroughly investigated using some metal ions including Mg2+, Mn2+, Pb2+, Ca2+, Fe3+, K+, Ag+, Zn2+, Co2+, Ni2+, Cd2+ and Hg2+ as potential interferences. Fig. 5 presents the fluorescence intensities of 4.0 × 10-6 mol L-1 NAC capped CdHgSe QDs solution before and after being interacted with the corresponding metal ions at the concentration of 4.0 × 10-6 mol L-1. Remarkably, it can be seen that copper ions can lead to the dramatic decrease of the fluorescence intensity. In the cases of Ag+, Co2+ and Hg2+, the changes of the fluorescence intensity were also notable, especially for Hg2+, meaning the positive interference on the determination of Cu2+. However, Cu2+ showed significantly higher ability to quench the fluorescence of the NAC capped

12

CdHgSe QDs than other investigated ions. The reason is not fully clear until now. Following viewpoints may be employed to interpret the experimental phenomenon. Compared with other transition-metal ions, Cu2

+

ion has higher thermodynamic

affinity and faster chelating processes towards ligands with “N” or “O” as the chelating atom (de Silva et al.,1997; Kramer et al., 1998). In the test solution, the NAC capped CdHgSe QDs are negatively charged. As a result, the metal cation Cu2+ and the NAC capped CdHgSe QDs will form a complex. Here, Cu2+ is a well-known paramagnetic ion which possesses d-orbit configuration with electron deficiency. Besides the strong electrostatic interaction, Cu2+ can also work as cationic electron acceptors, which will induce an ultrafast photoinduced electron transfer from the chromophore to copper ions and form a non-fluorescent ground state complex, resulting in quenching fluorescence (Xie et al., 2011). Furthermore, the paramagnetism and heavy metal effect of Cu(II) may cause electron spin-orbit coupling and transform the excited single-line state into the triplet state, which deactivates fluorescence by molecular internal conversion (Hu et al., 2009). In addition, using the percentage of change in fluorescence intensity is lower than 5.0% as standard, the tolerance of some potential interferents such as bovine serum albumin and amino acids etc. on the determination of 1.0 × 10-8 molL-1 Cu2+ were also studied. The results were summarized in Table 1. It can be seen that all substances tested at the given concentrations have no interference on the determination of Cu2+. These data demonstrated that the as-prepared NAC capped CdHgSe QDs can serve as novel fluorescence probe for the selective determination of Cu2+.

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3.5 Practical application To evaluate the practical utilities of the NAC capped CdHgSe QDs, the developed method was employed to determine Cu2+ in shrimp samples and water samples collected from South-lake (Wuhan, China) with standard addition method. Prior to being determined, shrimp samples were decorticated and the tail edible part was digested. The calculated average concentration for Cu2+ in the shrimp samples was 5.319 μg g-1 (n = 5, RSD = 4.6%). The recoveries for the addition of Cu2+ into shrimp samples were in the range of 93.71 ~ 103.4%. Atomic absorption spectroscopy was also used to analysis Cu2+ in shrimp samples, the average content was 5.083 μg g-1 (n =5, RSD = 2.3%), which was consistent with that obtained from the developed method. In the case of South-lake water determination, the samples were filtered with 0.45 µm membranes, and then the concentrations of Cu2+ were determined using the mentioned above method. The average concentration of Cu2+ in the collected water samples was 0.08013 µg mL-1 (n=5, RSD = 1.4%). The calculated result of Cu2+ concentration from atomic absorption spectroscopy was 0.083 μg mL-1 (n = 3, RSD = 3.1%). The relative error between the result from the developed method and atomic absorption spectroscopy is just only 1.8%. Recoveries for the three injections of the Cu2+ standard solution into water samples were ranged from 98.3% to 101.6%, and also demonstrated the accuracy of the NAC capped CdHgSe QDs for Cu2+ determination. All results indicated that the NAC capped CdHgSe QDs is a promising and reliable tool for the determination of Cu2+, and possesses potential applications in

14

the relevant real samples analysis. 4. Conclusions In conclusion, a simple and cost-effective fluorescence probe based on the NAC capped CdHgSe QDs has been developed for the selective determination of Cu2+. Compared with the reported fluorescent probes for Cu2+ determination, the developed method shows superior selectivity and lower detection limit. Unlike previously reported QDs-based Cu2+ assays which relies on interparticle crosslinking aggregation, this method is a novel design using the specific and strong coordination reaction between NAC and Cu2+. Meanwhile, Cu2+ can be simply and rapidly assayed by using the NAC capped CdHgSe QDs without complicated instruments. These remarkable properties endow the as-prepared NAC capped CdHgSe QDs with a great promise for practical applications. References Afkhami A., Soltani-Felehgari F., Madrakiana Tayyebeh., Ghaedi H., Rezaeivala M., 2013. Analytica Chimica Acta 771, 21 – 30. Alies B., Bijani C., Sayen S., Guillon E., Faller P., Hureau C., 2012. Inorganic Chemistry 51, 12988 − 13000. Becker J.S., Matusch A., Depboylu C., Dobrowolska J., Zoriy M.V., 2007. Analytical Chemistry 79, 6074 – 6080. Boman G., Backer U., Larsson S., Melander B., Wählinder L., 1983. European Journal of Respiratory Diseases 64, 405 – 415. Bruijn L.I., Miller T.M., Cleveland D.W., 2004. Annual Review of Neurosciences 27,

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723 – 749. Chen H., Cui S., Tu Z., Ji J., Zhang J., Gu Y., 2011. Photochemistry and Photobiology 87, 72 – 81. Chen J.L., Gao Y.C., Xu Z.B., Wu G.H., Chen Y.C., Zhu C.Q., 2006. Analytica Chimica Acta 577, 77 – 84. Chen S., Zhang X., Zhang Q., Hou X., Zhou Q., Yan J., Tan W., 2011. Journal of Luminescence 131, 947 – 951. Chen Y., Rosenzweig Z., 2002. Analytical Chemistry 74, 5132 – 5138. Chen Z., Wang L., Zou G., Tang J., Cai X., Teng M., Chen L., 2013. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105, 57 – 61. Choi A.O., Cho S.J., Desbarats J., Lovric J., Maysinger D., 2007. Journal of Nanobiotechnology 5, 1 – 13. de Silva A. P., Gunaratne H. Q. N., Gunnlaugsson T., Huxley A. J. M., McCoy C. P., Rademacher J. T., Rice T. E., 1997. Chemical Reviews 97, 1515 – 1566. Duan J.L., Jiang X.C., Ni S.Q., Yang M., Zhan J.H., 2011. Talanta 85, 1738 – 1743. Fernández-Argüelles M.T., Jin W.J., Costa-Fernández J.M., Pereiro R., Sanz-Medel A., 2005. Analytica Chimica Acta 549, 20 – 25. Gattás-Asfura K.M., Leblanc R.M., 2003. Chemical Communication 21, 2684 – 2685. Hankare P.P., Bhuse V.M., Garadkar K.M., Delekar S.D., Bhagat P.R., 2004. Semiconductor Science and Technology 19, 277 – 284. Harrison M.T., Kershaw S.V., Burt M.G., Eychmüller A., Weller H., Rogach A.L., 2000. Materials Science and Engineering B 69 – 70, 355 – 360.

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He Q., Shi J., Cui X., Zhao J., Chen Y., Zhou J., 2009. Journal of Materials Chemistry 19, 3395 – 3403. Hu M.B., Li H.X., Chen L.S., Zhang H.B., Dong C., 2009. Chinese Journal of Chemistry, 27, 513—517 Isarov A.V., Chrysochoos J., 1997. Langmuir, 13, 3142 – 3149. James L.P., McCullough S.S., Lamps L.W., Hinson J.A., 2003. Toxicological Sciences 75, 458 – 467. Koneswaran M., Narayanaswamy R., 2009. Sensors and Actuators B 139, 104 – 109. Kramer R., 1998. Angewandte Chemie International Edition 37, 772 – 773. Li F., Wang J., Lai Y., Wu C., Sun S., He Y., Ma H., 2013. Biosensors and Bioelectronics 39, 82 – 87. Li P., Duan X., Chen Z., Liu Y., Xie T., Fang L., Li X., Yin M., Tang B., 2011. Chemical Communication 47, 7755 – 7757. Lin T.W., Huang S.D., 2001. Analytical Chemistry 73, 4319 – 4325. Liu Z.Q., Liu S.P., Yin P.F., He Y.Q., 2012. Analytica Chimica Acta 745, 78 – 84. Liu H.Y., Zhang X., Wu X.M., Jiang L.P., Burda C., Zhu J.J., 2011. Chemical Communications 47, 4237 – 4239. Lovrić J., Bazzi H.S., Cuie Y., Fortin G.R., Winnik F.M., Maysinger D., 2005. Journal of Molecular Medicine 83, 377 – 385. Pei J.Y., Zhu H., Wang X. L., Zhang H.C., Yang X.R., 2012. Analytica Chimica Acta, 757, 63 – 68. Prescott L. F., Illingworth R.N., Critchley J. A. J. H., Stewart M. J., Adam R. D., Proudfoot A.T., 1979. British Medical Journal 2, 1097 – 1100.

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Rogach A.L., Euchmüller A., Hickey S.G., Kershaw S.V., 2007. Small 3, 536 – 557. Särnstrand B., Tunek A., Sjödin K., Hallberg A., 1995. Chemico-Biological Interactions 94, 157 – 164. Tiffany-Castiglioni E., Hong S., Qian Y., 2011. International Journal of Developmental Neuroscience 29, 811 – 818. Waggoner D.J., Bartnikas T.B., Gitlin J.D., 1999. Neurobiology of Disease 6, 221 – 230. Wang Y., Ye C., Wu L., Hu Y., 2010. Journal of Pharmaceutical and Biomedical Analysis 53, 235 – 242. Xiang, Y., Tong, A., Lu, Y., 2009. Journal of the American Chemical Society 131, 15352 – 15357. Xie X. J., Qin Y., 2011, Sensors and Actuators B 156, 213–217. Yang X., Pan Z., Ma Y., 2003. Journal of Analytical Science 19, 588 – 589. You Y., Han Y., Lee Y.M., Park S.Y., Nam W., Lippard S.J., 2011. Journal of the American Chemical Society 133, 11488 – 11491. Zhang L., Zhu J., Ai J., Zhou Z., Jia X., Wang E., 2013. Biosensors and Bioelectronics 39, 268 – 273. Zietz B.P., Dieter H.H., Lakomek M., Schneider H., Keßler-Gaedtke B., Dunkelberg H., 2003. The Science of the Total Environment 302, 127 – 144.

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Table 1 Influence of potential interferences on the fluorescence response of 1.0 × 10-8 molL-1 Cu2+. Foreign ions

Coexisting

Change of

Foreign

ions

Coexisting

Change of -1

concentration(

fluorescence

mol L-1)

intensity ( %)

Mg2+

1.50×10-5

3.8

K+

2.00×10-5

3.5

Mn2+

1.00×10-6

3.8

BSA

5.00×10-6

-3.6

Pb2+

1.20×10-5

-4.6

L-Valine

3.50×10-5

-3.5

Hg2+

5.00 ×10-8

4.5

L-Proline

1.00×10-5

-4.4

Cd2+

1.00×10-6

3.8

L-Phenylanine

2.50×10-5

-4.1

Fe3+

2.00×10-7

-3.9

L-Histidine

3.50×10-5

-3.5

Ag+

1.00×10-6

-3.6

L-Lysine

7.00×10-5

4.0

Zn2+

1.20×10-5

-5.0

L-Glycine

3.50×10-5

-3.7

Co2+

2.00×10-6

-4.4

L-glutamic acid

7.00×10-5

-3.6

Ni2+

3.00×10-6

-5.2

L-cysteine

5.00×10-6

-4.6

Ca2+

2.50×10-5

-4.4

concentration(mol L )

fluorescence intensity ( %)

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Fig. 1 Characterization of the NAC capped CdHgSe QDs with TEM (a), XRD (b) and FTIR (c, curve II). Curve I is the FTIR spectrum of NAC. Fig. 2 Effect of pH values on the fluorescence intensity change (ΔI) of 5.9 × 10-5 mol L-1 NAC capped CdHgSe QDs before and after being interacted with 1 × 10-7 mol L-1 Cu2+. Fig.3 (A) Fluorescence spectra of 5.9 × 10-5 mol L-1 NAC capped CdHgSe QDs before (a) and after being interacted with 1 × 10-9 (b), 2 × 10-8 (c), 6 × 10-8 (d), 1 × 10-7 (e), 2 × 10-7 (f), 2.4 × 10-7 (g), 3 × 10-7 (h), 4 × 10-7 (i) mol L-1 Cu2+; (B) Calibration curve for Cu2+ determination; The inset is the enlargement of the calibration curve for Cu2+ determination at low concentration. Fig. 4 UV-Vis spectra of the NAC capped CdHgSe QDs (a), the NAC capped CdHgSe QDs with addition of 2 × 10-7 mol L-1 Cu2+ (c), and the NAC capped CdHgSe QDs with addition of 2 × 10-7 mol L-1 Cu2+ and 1.0 × 10-4 mol L-1 EDTA (b). The NAC capped CdHgSe QDs concentration is 5.9 × 10-5 mol L-1. Fig. 5 Fluorescence response of 4.0 × 10-6 mol L-1 NAC capped CdHgSe QDs towards different metal ions at the concentration of 4.0 × 10-6 mol L-1.

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Figure legends

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Fig. 5

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Highlights ► Facilely synthesize N-acetyl-L-cysteine capped CdHgSe (NAC-CdHgSe) QDs in aqueous phase; 2+ ► Fluorescent characteristics of NAC-CdHgSe QDs and its interaction with Cu ; 2+ ► Selective fluorescent sensing of Cu ; 2+ ►Successfully determine Cu in shrimp samples.

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Fluorescent sensor for selective determination of copper ion based on N-acetyl-L-cysteine capped CdHgSe quantum dots.

Using N-acetyl-L-cysteine as a stabilizer, well water-dispersed, high-quality and stable CdHgSe quantum dots were facilely synthesized via a simple aq...
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