Detection of sparfloxacin based on water-soluble CuInS2 quantum dots

Detection of sparfloxacin based on water-soluble CuInS2 quantum dots

Results in Chemistry 2 (2020) 100027 Contents lists available at ScienceDirect Results in Chemistry journal homepage:

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Results in Chemistry 2 (2020) 100027

Contents lists available at ScienceDirect

Results in Chemistry journal homepage:

Detection of sparfloxacin based on water-soluble CuInS2 quantum dots Jiajia Fang, Beina Dong, Yingqiang Fu ⁎, Dingxing Tang ⁎ College of Biological and Chemical Engineering, Anhui Polytechnic University, Wuhu, Anhui 241000, PR China

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Article history: Received 7 September 2019 Accepted 7 January 2020 Available online xxxx Keywords: Sparfloxacin Quantum dots Fluorescence

a b s t r a c t Thioglycolic acid-modified CuInS2 quantum dots were prepared by a hydrothermal method. A method for the determination of sparfloxacin by a CuInS2 ternary-quantum dot fluorescence probe was established based on the fact that the fluorescence of CuInS2 quantum dots can be significantly quenched by sparfloxacin. The optimized experimental conditions are as follows: (1) the concentration of CuInS2 quantum dots is 0.4 mol·L−1; (2) the pH of the buffer solution is 6, and 1 mL of buffer was used; (3) the reaction time is 5 min. The concentration of sparfloxacin is linearly related to the fluorescence quenching intensity from 0.5 μg/mL to 1 mg/mL, and the maximum detection limit is 1 mg/mL. © 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (

1. Introduction Sparfloxacin (SPFX) is a third-generation quinolone antibiotic. Compared with other quinolone antibiotics, SPFX not only has broadspectrum antibacterial activity, high potency, high permeability, a long half-life and other desirable pharmacokinetic characteristics but also shows high efficacy, good tolerance and other advantages [1–3]. Because of its long half-life and few side effects, it has been widely used in the treatment of infectious diseases in animal husbandry and for promoting growth in fish breeding [4,5]. At present, the problems associated with the safety of animal-derived foods caused by nonstandard SPFX use are becoming increasingly serious. At present, SPFX residue detection is mainly conducted by quantitative methods. For example, high-performance liquid chromatography and capillary zone electrophoresis can be used for quantitative analysis, and liquid chromatography-mass spectrometry or gas chromatography– mass spectrometry can be used for confirmation [6,7]. These methods require cumbersome sample processing steps and are not broadly applicable, so a fast, convenient, sensitive and practical detection method was developed to effectively prevent the illegal abuse of SPFX and provide a technique for confirming food safety. Quantum dots (QDs), also known as semiconductor nanocrystals, are nanomaterials with three-dimensional constraints. Due to their unique optical and electronic properties, high specific surface area, quantum size effect and other characteristics, they have attracted extensive attention from scholars around the world [8–10]. In recent years, ⁎ Corresponding author. E-mail address: [email protected] (Y. Fu).

QDs have been widely used in medical, biological and environmental detection as highly sensitive, selective and economical luminescent sensors for the detection of toxic metals [11], pesticides [12], explosives [13], drugs [14] and a various biological molecules [15]. QDs have been used for SPFX detection. Such as Water-soluble CdSe/CdS [16] and CdTe [17] QDs. These methods have been confirmed as a sensitive, precise and convenient detection method for SPFX. However, these QDs are not easy to synthesize, Synthesis of them usually requires inert gas protection and higher requirements for synthetic techniques of experimental operators. Among the QDs recently reported, CuInS2 QDs contain neither toxic cations, such as Cd or Pb ions, nor toxic anions, such as As or Se ions. According to previous reports [18], CuInS2 QDs also have very good fluorescence properties. The synthesis method is relatively simple and environmentally friendly, so these QDs can be produced on a large scale, making them practically useful. In this work, CuInS2 QDs were synthesized by a one-step hydrothermal method according to the previously reported [19] method with a modification, and a new fluorescence-based method for detecting SPFX was established by using CuInS2 QDs as fluorescent probes (Scheme 1).

2. Experimental section 2.1. Apparatus and reagents Apparatus: S82-1 magnetic stirrer (Shanghai Zhiwei Co., Ltd., China), F-4500 fluorescence spectrophotometer (Hitachi Limited, Japan), HH-2 thermostatic water bath (Jintan Jalier Electric Appliance Co., Ltd., China), and JK-300cde high-frequency numerical control ultrasonic cleaner 2211-7156/© 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (


J. Fang et al. / Results in Chemistry 2 (2020) 100027

Scheme 1. Interaction mode of CuInS2 QDs with sparfloxacin (SPFX) and the fluorescence quenching mechanism.

(Hefei Jinnick Machinery Manufacturing Co., Ltd., China), X-ray powder diffractometer (Bruker, Germany). Reagents: CuCl2·2H2O, InCl3·4H2O, 3-mercaptopropionic acid (MPA, 99%), NaOH, Na2HPO4, and NaH2PO4 were purchased from Aladdin Biochemistry Technology Co., Ltd. Sparfloxacin was purchased from Shanghai Yuanye Biotechnology Co., Ltd.

2.2. Synthesis of CuInS2 QDs CuCl2·2H2O (0.0768 g) and 0.1320 g of InCl3·4H2O were dissolved in 31.5 mL of deionized water, and then 0.5850 g of 3-mercaptopropionic acid was added with stirring. Sodium hydroxide solution (2 mol/L) was added to adjust the pH of the solution to 11, and the solution was stirred for 10 min. Then, 0.0684 g of thiourea solution was added. Once the solids had completely dissolved into 50 mL of liquid in the reaction kettle, the solution was places in a 150 °C oven for 21 h. After the reaction, the solution was allowed to cool naturally to room temperature. The product was obtained as a pale-yellow transparent solution. Ethanol was added at a 1:10 volume ratio following centrifugation. The supernatant was then dried at 60 °C, affording the CuInS2 QDs as a powder.

3.2. The detection of QDs To ensure the feasibility of detecting sparfloxacin using CuInS2 QDs, we first confirmed the effect of sparfloxacin on the absorbance and fluorescence intensity of CuInS2 QDs. As shown in Figs. 3 and 4 respectively, when the standard solution of sparfloxacin was added to the CuInS2 QDs, the absorbance no significant change, however, the fluorescence intensity of the QDs decreased significantly, and the fluorescence emission peak also slightly blue shifted with increasing sparfloxacin concentration. Therefore, a method for the determination of sparfloxacin content based on fluorescence quenching is possible.

3.3. Detection of sparfloxacin base on the quenching of CuInS2 QDs 3.3.1. Effect of CuInS2 QD concentration Fig. 5 shows that when the concentration of copper indium sulfur QDs is 0.2 × 10−3–0.4 × 10−3 mol/L, the fluorescence quenching intensity(ΔF) increases; when the QD concentration is 0.4 × 10−3–1 × 10−3 mol/L, the

2.3. Determination of sparfloxacin The CuInS2 QDs (4 × 10−5 mol. L−1), 0.25 mL of Na2HPO4-NaH2PO4 buffer (pH = 6), and a certain amount of SPFX were sequentially added to 10-mL colorimetric tubes. Distilled water was added to the dilute the solution, and it was thoroughly mixed. After standing for 10 min at room temperature, the fluorescence intensity, F0, and F of the blank solution (solution without SPFX), were determined at an excitation wavelength of 262 nm and an emission wavelength of 530 nm, and F refers to the fluorescence quenching intensity of the system (△F=F-F0). 3. Results and discussion 3.1. Characterization of CuInS2 QDs Fig. 1 shows HR-TEM micrographs of the CuInS2 QDs produced after 21 h reaction at 150 °C. The nanoparticles have small diameters with a narrow size distribution (4.7 ± 0.3 nm). Fig. 2 shows the XRD pattern of CuInS2 synthesized by the hydrothermal method. We found signals at 2 theta values of 27.8°, 28.9°, 32.4°, 46.2°, 46.5°, 50.2°, 54.7° and 74.5° and faces (112), (103), (200), (204), (220), (301), (116) and (316) indicative of tetragonal copper indium sulfur (PDF card (27–0159)). No diffraction peaks of other substances were observed in the data, indicating that the product was a pure CuInS2 phase.

Fig. 1. The HR-TEM image of CuInS2 QDs.

J. Fang et al. / Results in Chemistry 2 (2020) 100027


fluorescence quenching intensity(ΔF) is relatively weak. When the QD concentration is high, the fluorescence intensity(ΔF) is above the limit of the detector. Therefore, the optimal concentration of copper indium sulfur QDs is 0.4 × 10−3 mol/L, and this concentration was used for further experiments. 3.3.2. Effect of pH on △F As shown in Fig. 6, the experimental results show that a buffer pH of 6 resulted in the highest fluorescence quenching intensity(ΔF). In addition, the effect of the volume of buffer solution on the fluorescence of the system was studied, and the results showed that the fluorescence quenching was most effective when 1 mL of buffer was used. 3.3.3. Effects of temperature, mixing order, and reaction time No obvious changes in fluorescence quenching were achieved by varying the temperature in the range of 20–50 °C. The order of addition to the solution has no obvious influence on the experimental results. After the addition of sparfloxacin, the fluorescence intensity of the QDs remained stable for 10 min and remained relatively unchanged over the next 90 min. Therefore, for the sake of operational simplicity, SPFX was mixed with the CuInS2 QDs at room temperature, and then

Fig. 2. CuInS2 QDs XRD image.

Fig. 3. Absorbance of CuInS2 quantum dots with sparfloxacin.


CuInS2QDs+SPFX(30μg·mL )

Fluorescence intensity(a.u.)



CuInS2QDs+SPFX(10μg·mL ) CuInS2QDs

3000 2000 1000 0 500






Wavelength(nm) Fig. 4. Fluorescence emission spectra of CuInS2 quantum dots with different concentrations of sparfloxacin standard solution.


J. Fang et al. / Results in Chemistry 2 (2020) 100027

1600 1400 1200


1000 800 600 400 200 2


6 -3




C(10 moL·L ) Fig. 5. Effect of CuInS2 quantum dot concentration on fluorescence quenching intensity of the system.

the buffer was added. The volume was adjusted with distilled water, and the solution was mixed thoroughly for 10 min before fluorescence detection. 3.4. Calibration curves and detection limits Drug concentration (C) as the abscissa and Δ F as the ordinate were plotted to prepare a scatter diagram (Fig. 7A). There is a relationship between the two variables, but it is not a linear relationship. When the logarithm of concentration C was plotted on the abscissa of a scatter diagram (Fig. 7B), logC was found to be linearly related to Δ F. Fig. B shows the linear regression (Δ F = 375.71 logC +481.12), and this calibration equation has a very high R2 of 0.994. When the drug concentration was further increased or decreased, the detection results significantly deviated from the calibration curve, so the minimum detection limit of this detection method is 0.5 μg/mL and the maximum detection limit is 1 mg/mL. 3.5. Interference study The interference of several common coexisting substances with the standard solution detection system for sparfloxacin was investigated.

As shown in Fig. 8, Na+, K+, Ca2+, Cl− and NO− 3 at concentrations 100 times greater than that of the drug and L-cysteine, L-serine, glycine and starch at concentrations 200 times that of the drug had no significant influence on the detection of sparfloxacin at 10 μg/mL, and the relative error was b5%. This method has good selectivity for the detection of sparfloxacin.

3.6. Determination of sparfloxacin in tablets To further verify the feasibility of using the established method for the analysis of actual samples, a standard additive recovery experiment was carried out using sparfloxacin tablets, and the results are shown in Table 1.

4. Conclusion In this work, CuInS2 QDs were used as fluorescence probes for the rapid and simple determination of trace sparfloxacin. This method has the advantages of high sensitivity, operational simplicity, low cost and good selectivity, making it suitable for practical sample analysis.

800 700


600 500 400 300 200 100





pH Fig. 6. Effect of pH on fluorescence quenching intensity of the system.


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Table 1 Determination of SPFX in tablets. Initial (μg∙mL−1)

Total RSD (%) Added (n = 5) (μg∙mL−1) (μg∙mL−1) (n = 5)

9.85 9.33 10.51 9.67 10.83 1.2

5 10 15

15.17 19.88 25.34

Recovery (%) (n = 5) 103.8 97.6 102.3


Fig. 7. Linear relationship between SPFX and fluorescence intensity difference of CuInS2 QDs.


Normalized Intensity (a·u·)

The authors gratefully acknowledge the support of this study by the National Natural Science Foundation of China (21406001).

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1.2 1.0 0.8 0.6 0.4 0.2 0.0







The added substance Fig. 8. Interference fluorescence of coexisting substances.


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