Norfloxacin detection method and preparation method of fluorescence detection material

Abstract

The present invention discloses a method for detecting norfloxacin and a method for preparing a fluorescent detection material, which solves the technical problems of insufficient fluorescence change, poor specificity and poor anti-interference ability in the prior art. The method for detecting norfloxacin adopts N, S-CDs, wherein the N, S-CDs are carbon dots co-doped with nitrogen and sulfur; the first fluorescence intensity of the liquid to be tested and the second fluorescence intensity of the mixture of the liquid to be tested and the N, S-CDs are detected, and the concentration of norfloxacin in the liquid to be tested is converted according to the linear relationship between the ratio of the second fluorescence intensity to the first fluorescence intensity and the concentration of norfloxacin. The method for preparing a fluorescent detection material for detecting norfloxacin comprises the following steps: (1) obtaining a mixed solution including ammonium citrate and L-cysteine; (2) heat-treating the mixed solution; (3) dispersing the heat-treated product in water, and then centrifuging; (4) dialyzing the supernatant obtained by centrifugation to obtain an N, S-CDs aqueous solution for detecting norfloxacin.

Description

Technical Field

[0001] The invention relates to the technical field of norfloxacin detection, and in particular to a norfloxacin detection method and a method for preparing a fluorescent detection material. Background Art

[0002] Norfloxacin (NOR) is a fluoroquinolone drug widely used in medicine. NOR causes infections such as lung, urine and digestive system infections against Gram-positive, Gram-negative bacteria and mycoplasma. In recent years, fluoroquinolones have accumulated in the environment, posing a threat to ecosystems and human health, and it is crucial to develop a sensitive and effective method for detecting NOR in the environment. So far, many analytical methods have been reported for detecting NOR, such as electrochemical analysis, chemiluminescence, high performance liquid chromatography (HPLC), UV-visible spectrophotometry, titration, etc. However, these analytical methods are limited in practical application, for example, they require heating or extraction steps, involve expensive reagents and cumbersome sample pretreatment, show a narrow linear response range and time consumption, etc. Therefore, it is necessary to develop a fast, simple and low-cost method for the effective determination of NOR.

[0003] Fluorescence spectroscopy has attracted much attention due to its advantages such as simple operation, low detection limit, fast response time, high specificity and sensitivity, and strong practicality. Carbon dots (CDs) are a special type of fluorescent nanomaterials with bright fluorescence, high photostability, good biocompatibility, and excellent water solubility. Therefore, it is highly feasible to use carbon dots as fluorescent probes and apply them to the detection of norfloxacin in water. However, the applicant has found in practice that due to the small degree of fluorescence change, poor specificity (especially for the recognition of antibiotic drugs) and poor anti-interference ability, simple carbon dots cannot be used to detect trace norfloxacin in water. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for detecting norfloxacin and a method for preparing a fluorescence detection material, so as to solve the technical problems of insufficient fluorescence change, poor specificity and poor anti-interference ability in the prior art.

[0005] In order to achieve the above object, according to the first aspect of the present invention, a method for detecting norfloxacin is provided, and the technical scheme is as follows:

[0006] The method for detecting norfloxacin adopts N, S-CDs, wherein the N, S-CDs are carbon dots co-doped with nitrogen and sulfur; a first fluorescence intensity of a test liquid and a second fluorescence intensity of a mixture of the test liquid and the N, S-CDs are detected, and the concentration of norfloxacin in the test liquid is converted according to a linear relationship between a ratio of the second fluorescence intensity to the first fluorescence intensity and the concentration of norfloxacin.

[0007] As a further improvement of the first aspect of the present invention, the linear relationship is: y=0.01709x+1.01243, R 2 =0.997, x is the norfloxacin concentration, x is 0.5-50 μmol / L, and y is the ratio of the second fluorescence intensity to the first fluorescence intensity.

[0008] As a further improvement of the first aspect of the present invention, the pH of the test environment is 2-6; the reaction temperature of the test liquid and N, S-CDs is 20-30°C; and the reaction time of the test liquid and N, S-CDs is 1-5 minutes.

[0009] As a further improvement of the first aspect of the present invention, the XPS full energy spectrum of N,S-CDs has characteristic peaks at 400.1eV, 231.1eV and 163.81eV; the XPS spectrum of N,S-CDs at N1s has characteristic peaks at 398.8eV and 400.9eV; the XPS spectrum of N,S-CDs at S2p has characteristic peaks at 164.2eV and 163.2eV.

[0010] As a further improvement of the first aspect of the present invention, the FIRT spectrum of N,S-CDs is at 3432 cm -1 、3180cm -1 、1581cm -1 、1405cm -1 、1250cm -1 and 615cm -1 There are characteristic peaks.

[0011] As a further improvement of the first aspect of the present invention, the preparation of N,S-CDs comprises the following steps: heat-treating and purifying a mixture of ammonium citrate and L-cysteine ​​to obtain N,S-CDs.

[0012] In order to achieve the above object, according to the second aspect of the present invention, a method for preparing a fluorescent detection material for detecting norfloxacin is provided, and the technical scheme is as follows:

[0013] The method for preparing a fluorescent detection material for detecting norfloxacin comprises the following steps:

[0014] (1) obtaining a mixed solution including ammonium citrate and L-cysteine;

[0015] (2) heat treating the mixed solution;

[0016] (3) dispersing the heat-treated product in water and then centrifuging it;

[0017] (4) The supernatant obtained by centrifugation is dialyzed to obtain an N,S-CDs aqueous solution for detecting norfloxacin.

[0018] As a further improvement of the second aspect of the present invention, the mass ratio of ammonium citrate to L-cysteine ​​in the mixed solution is 2-2.4, and the mixed solution is prepared by adding 0.8-1.2 g L-cysteine ​​to every 10 mL of water.

[0019] As a further improvement of the second aspect of the present invention, the heat treatment temperature is 170-190° C., and the time is 60-90 min; the dialysis treatment uses a dialysis bag with a molecular weight cutoff of 1000 Da, and the dialysis time is 18-30 h.

[0020] As a further improvement of the second aspect of the present invention, the method further includes subjecting the mixed solution to ultrasonic treatment before heat treatment; and filtering the supernatant obtained by centrifugation.

[0021] First, the detection method of norfloxacin of the present invention utilizes carbon dots co-doped with nitrogen and sulfur to perform fluorescence detection on norfloxacin, which is not only simple in process and easy to operate, but also has a high degree of fluorescence change, a wide linear range, a low detection limit, can specifically identify norfloxacin, and has strong anti-interference ability, effectively solving the technical problem that norfloxacin in water is difficult to detect. Secondly, the preparation process of the carbon dots co-doped with nitrogen and sulfur of the present invention is simple and controllable, and the production cost is low. It can be seen from this that the detection method of norfloxacin of the present invention and the preparation method of the fluorescence detection material are highly practical and very suitable for promotion and use.

[0022] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings constituting a part of the present invention are used to assist in understanding the present invention. The contents provided in the drawings and their related descriptions in the present invention can be used to explain the present invention, but do not constitute improper limitations on the present invention. In the drawings:

[0024] Figure 1 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with the mass ratio of ammonium citrate and L-cysteine.

[0025] Figure 2This is the curve of F1-F0 of N,S-CDs aqueous solution changing with heat treatment temperature.

[0026] Figure 3 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with heat treatment time.

[0027] Figure 4 TEM and HR-TEM images of N,S-CDs powder (inset).

[0028] Figure 5 This is the particle size distribution diagram of N,S-CDs obtained under the optimal preparation process parameters.

[0029] Figure 6 Fourier transform infrared spectrum of N,S-CDs powder.

[0030] Figure 7 This is the full energy spectrum of X-ray photoelectron spectroscopy of N,S-CDs powder.

[0031] Figure 8 This is the XPS spectrum of N,S-CDs powder at C1s.

[0032] Fig. 9 XPS spectrum of N,S-CDs powder at N1s.

[0033] Fig.10 This is the XPS spectrum of N,S-CDs powder at O1s.

[0034] Fig.11 XPS spectrum of N,S-CDs powder at S2p.

[0035] Fig.12 Fluorescence lifetime diagrams of N,S-CDs aqueous solution and N,S-CDs+NOR (a mixture of N,S-CDs aqueous solution and norfloxacin solution).

[0036] Fig.13 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with the pH of the test environment.

[0037] Fig.14 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with reaction temperature.

[0038] Fig.15 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with reaction time.

[0039] Fig.16 This is a comparison chart of the effects of detecting different antibiotics in N,S-CDs aqueous solution.

[0040] Fig.17These are the test results of the anti-interference performance of N,S-CDs aqueous solution.

[0041] Fig.18 Fluorescence spectra of N,S-CDs aqueous solution testing norfloxacin solutions of different concentrations.

[0042] Fig.19 This is the linear fitting curve between F1 / F0 of N,S-CDs aqueous solution and norfloxacin concentration. DETAILED DESCRIPTION

[0043] The present invention is described clearly and completely below in conjunction with the accompanying drawings. A person skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that:

[0044] The technical solutions and technical features provided in each part of the present invention, including the following description, may be combined with each other if there is no conflict.

[0045] In addition, the embodiments of the present invention involved in the following description are generally only a part of the embodiments of the present invention, rather than all the embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0046] About the terms and units in the present invention: The terms "include", "have" and any variations thereof in the description and claims of the present invention and related parts are intended to cover non-exclusive inclusions.

[0047] An embodiment of the method for preparing a fluorescent detection material for detecting norfloxacin (NOR) of the present invention comprises the following steps:

[0048] (1) obtaining a mixed solution including ammonium citrate and L-cysteine;

[0049] (2) heat treating the mixed solution;

[0050] (3) dispersing the heat-treated product in water and then centrifuging it;

[0051] (4) The supernatant obtained by centrifugation is dialyzed to obtain a fluorescent detection material for detecting norfloxacin (i.e., N,S-CDs aqueous solution).

[0052] The mass ratio of ammonium citrate to L-cysteine ​​in the mixed solution is 2 to 2.4, and can be, but is not limited to, any one of 2, 2.1, 2.2, 2.3, and 2.4.

[0053] The mixed solution is prepared by adding 0.8-1.2 g of L-cysteine ​​to every 10 mL of water, and the value can be but is not limited to any one of 0.8 g, 0.9 g, 1 g, 1.1 g, and 1.2 g.

[0054] In order to improve the uniformity of the carbon dot particle size, the mixed solution is ultrasonically treated before the heat treatment until a clear and transparent mixed solution is formed.

[0055] The heat treatment temperature is 170-190°C, and can be but not limited to any one of 170°C, 175°C, 180°C, 185°C, and 190°C. The heat treatment time is 60-90min, and can be but not limited to any one of 60min, 70min, 80min, and 90min.

[0056] The dialysis treatment uses a dialysis bag with a molecular weight cutoff of 1000Da, and the dialysis time is 18 to 30 hours, which can be but is not limited to any one of 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, and 30 hours.

[0057] In order to improve the efficiency of dialysis, the supernatant obtained by centrifugation is filtered, and the filtration is preferably carried out using a filter needle with a pore size of 0.2 to 0.25 μm. The pore size can be but is not limited to any one of 0.2 μm, 0.21 μm, 0.22 μm, 0.23 μm, 0.24 μm, and 0.25 μm.

[0058] The obtained N,S-CDs aqueous solution can be freeze-dried to obtain N,S-CDs powder, so as to determine the concentration of N,S-CDs in the N,S-CDs aqueous solution. It has been verified that the XPS full energy spectrum of N,S-CDs powder has characteristic peaks at 400.1eV, 231.1eV and 163.81eV; the XPS spectrum of N1s of N,S-CDs powder has characteristic peaks at 398.8eV and 400.9eV; the XPS spectrum of S2p of N,S-CDs powder has characteristic peaks at 164.2eV and 163.2eV. The FIRT spectrum of N,S-CDs is at 3432cm -1 、3180cm -1 、1581cm -1 、1405cm -1 、1250cm -1 and 615cm -1 There are characteristic peaks.

[0059] An embodiment of the method for detecting norfloxacin of the present invention is to use N, S-CDs, wherein the N, S-CDs are carbon dots co-doped with nitrogen and sulfur, preferably N, S-CDs powder or N, S-CDs aqueous solution prepared by the above-mentioned preparation method; when used, the first fluorescence intensity of the test liquid and the second fluorescence intensity of the mixture of the test liquid and the N, S-CDs aqueous solution are detected, and the concentration of norfloxacin in the test liquid is converted according to the linear relationship between the ratio of the second fluorescence intensity to the first fluorescence intensity and the norfloxacin concentration.

[0060] The linear relationship is: y=0.01709x+1.01243, R 2 =0.997, x is the norfloxacin concentration, x is 0.5-50 μmol / L, and y is the ratio of the second fluorescence intensity to the first fluorescence intensity.

[0061] The pH value of the test environment is 2-6, and can be, but is not limited to, any one of 2, 3, 4, 5, and 6.

[0062] The reaction temperature of the test solution and the N,S-CDs aqueous solution is 20-30°C, and can be, but is not limited to, any one of 20°C, 22°C, 24°C, 26°C, 28°C, and 30°C.

[0063] The reaction time between the test solution and the N,S-CDs aqueous solution is 1 to 5 minutes, and can be, but is not limited to, any one of 1 minute, 2 minutes, 3 minutes, 4 minutes, and 5 minutes.

[0064] The beneficial effects of the present invention are described below through specific characterization and experiments.

[0065] First, the effects of N,S-CDs aqueous solutions prepared by different mass ratios of ammonium citrate and L-cysteine, heat treatment temperatures and heat treatment times were compared. The other preparation parameters were as follows: 1g L-cysteine ​​was added to every 10mL water; 10mL water was used to dissolve the heat-treated product and then centrifuged at 100000rmp for 5min; the pore size of the filter needle was 0.22μm; the dialysis time was 24h; during fluorescence detection, the volume of N,S-CDs aqueous solution was 250μL (the same below), the volume of NOR solution was 250μL, and the concentration of NOR solution was 50μmol / L.

[0066] Figure 1 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with the mass ratio of ammonium citrate and L-cysteine. Figure 2 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with heat treatment temperature. Figure 3 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with heat treatment time.

[0067] from Figure 1-3 It can be seen that the optimal preparation process parameters of N,S-CDs aqueous solution are: the mass ratio of ammonium citrate to L-cysteine ​​is 2, the heat treatment temperature is 180 °C, and the heat treatment time is 60 min.

[0068] Figure 4 TEM and HR-TEM images of N,S-CDs powder (inset). Figure 5 This is the particle size distribution diagram of N,S-CDs obtained under the optimal preparation process parameters.

[0069] like Figure 4 As shown in the figure, N,S-CDs powder is highly dispersed in nano-spherical particles with a lattice spacing of 0.23nm, which is similar to graphite carbon (sp 2 ) corresponds to the diffraction surface.

[0070] By using Image J software Figure 4 The particle size of nano-spherical particles was statistically analyzed. Figure 5 The nanoparticle size distribution histogram is shown. Figure 5 As shown, the particle diameter of N,S-CDs powder is distributed in the range of 1 to 5 nm, and the average particle diameter is about 2.62 nm.

[0071] Figure 6 Fourier transform infrared spectrum (FT-IR) of N,S-CDs powder.

[0072] like Figure 6 As shown, at 3432cm -1 and 3180cm -1 The two broad peaks at 1581 cm-1 correspond to -OH and -NH, respectively. -1 and 1405cm -1 The two sharp peaks at 1250 cm-1 correspond to -COO and -C=O, respectively. -1 and 615cm -1 The two characteristic peaks at correspond to -C=S and -CH, respectively.

[0073] Figure 7 This is the X-ray photoelectron spectroscopy (XPS) full energy spectrum of N,S-CDs powder.

[0074] like Figure 7 As shown, the XPS full-energy spectrum of N,S-CDs has characteristic peaks at 532.87 eV, 400.1 eV, 285.81 eV, 231.1 eV and 163.81 eV, corresponding to O1s, N1s, C1s, S2s and S2p, respectively.

[0075] Figure 8 This is the XPS spectrum of N,S-CDs powder at C1s. Fig. 9 XPS spectrum of N,S-CDs powder at N1s. Fig.10 This is the XPS spectrum of N,S-CDs powder at O1s. Fig.11 XPS spectrum of N,S-CDs powder at S2p.

[0076] like Figure 8 As shown, the characteristic peaks of the XPS spectrum of C1s at 284.8 eV, 286.1 eV and 288.1 eV correspond to CC / C=C, CN / CO / CS and C=O, respectively. Fig. 9 As shown in Figure 2, the characteristic peaks of the XPS spectrum of N1s at 398.8 eV and 400.9 eV correspond to CNC and HN=C, respectively. Fig.10 As shown, the characteristic peaks of the XPS spectrum of O1s at 531.2eV, 532.1eV and 533.1eV correspond to C=O, COH and COC, respectively. Fig.11 As shown, the characteristic peaks of the XPS spectrum of S2p at 163.2 eV and 164.2 eV correspond to the CSC of S2p3 / 2 and the CSC of S2p1 / 2, respectively.

[0077] Fig.12 Fluorescence lifetime diagrams of N,S-CDs aqueous solution and N,S-CDs+NOR (a mixture of N,S-CDs aqueous solution and norfloxacin solution).

[0078] like Fig.12 As shown, the fluorescence decay was fitted with a double exponential function and the fluorescence lifetime of N,S-CDs-NOR was 1.94 ns, and that of N,S-CDs was 8.25 ns.

[0079] In the above representation:

[0080] TEM and HRTEM were performed using a FEI Talos F200x transmission electron microscope; FT-IR was performed using a Perkin-Lemmer Fourier transform infrared spectrometer from the United States; XPS was performed using a Thermo Scientific K-Alpha X-ray photoelectron spectrometer from Germany; and the fluorescence lifetime test was performed using a FLS1000 steady-state / transient fluorescence spectrometer (Edinburgh, UK).

[0081] Secondly, the effects of N,S-CDs aqueous solution under different detection conditions were compared.

[0082] Fig.13 This is the curve of F1-F0 of N,S-CDs aqueous solution changing with the pH of the test environment. Fig.14This is the curve of F1-F0 of N,S-CDs aqueous solution changing with reaction temperature. Fig.15 The curve of F1-F0 of N,S-CDs aqueous solution changing with reaction time. The volume of NOR solution is 250μL, and the concentration is 50μmol / L. After mixing the N,S-CDs aqueous solution with the norfloxacin solution, the pH of the test environment is adjusted with BR buffer.

[0083] from Figure 13-15 It can be seen that the optimal use condition parameters of N, S-CDs aqueous solution are: pH of the test environment = 4, the reaction time of N, S-CDs aqueous solution and norfloxacin solution is 1 min, and the reaction temperature is 20°C.

[0084] exist Figure 1-3 and Figure 12-15 In the figure, F0 is the fluorescence intensity of N,S-CDs aqueous solution, and F1 is the fluorescence intensity of N,S-CDs+antibiotics (i.e., a mixture of N,S-CDs aqueous solution and antibiotic solution).

[0085] Fig.16 This is a comparison chart of the effects of N,S-CDs aqueous solution on the detection of different antibiotics. The dosage of each antibiotic is 250μL, and the concentration is 50μmol / L. F0 is the fluorescence intensity of N,S-CDs aqueous solution, and F1 is the fluorescence intensity of N,S-CDs + antibiotics.

[0086] like Fig.16 As shown in the figure, the difference in fluorescence change before and after adding N,S-CDs aqueous solution to the test solution containing CIP (ciprofloxacin), ENR (enrofloxacin), OFX (ofloxacin), SMZ (sulfamethoxazole) or TC (tetracycline) is almost the same as the difference in fluorescence change before and after adding N,S-CDs dispersion to pure water, indicating that N,S-CDs can specifically recognize norfloxacin.

[0087] Fig.17 The test results of the anti-interference performance of N,S-CDs aqueous solution. F0 is the fluorescence intensity of N,S-CDs aqueous solution, and F1 is the fluorescence intensity of N,S-CDs+NOR+interfering ions; when interfering ions and NOR coexist, the volume of the interfering ion solution and the NOR solution is 125μL, and the concentration is 50μmol / L; 125μL of water is used to replace the interfering ion solution in the control.

[0088] like Fig.17 As shown, when norfloxacin and interfering ions coexist, the degree of fluorescence change (i.e., F1-F0) remains basically stable, indicating that N,S-CDs has good anti-interference ability for norfloxacin detection and can be applied to the detection of actual samples.

[0089] Then, the sensitivity, linear range, and practicality of N,S-CDs aqueous solution for testing norfloxacin were tested.

[0090] Fig.18 Fluorescence spectra of N,S-CDs aqueous solution testing norfloxacin solutions of different concentrations. Fig.19 is a linear fitting curve between F1 / F0 of N,S-CDs aqueous solution and norfloxacin concentration. F0 is the fluorescence intensity of N,S-CDs aqueous solution, i.e., the first fluorescence intensity, and F1 is the fluorescence intensity of N,S-CDs+NOR, i.e., the second fluorescence intensity.

[0091] from Fig.18 It can be seen that with the increase of norfloxacin concentration, the fluorescence intensity of N,S-CDs+NOR gradually increased. Fig.19 It can be seen that F1 / F0 shows a good linear relationship with the concentration of norfloxacin. When the concentration of norfloxacin is 0.5-50 μmol / L, the regression equation is y=0.01709x+1.01243, R 2 =0.997, and the detection limit of norfloxacin is 0.5 μmol / L.

[0092] The lake water from the campus of Southwest Jiaotong University and the tap water in the laboratory were selected as actual samples. After centrifugation for 10 minutes, they were filtered with a 0.45 μm filter membrane. Then, different concentrations of norfloxacin (5 μmol / L, 20 μmol / L, and 50 μmol / L) were added to the water samples. The concentration of norfloxacin in the water samples was tested using N, S-CDs and the above regression equation. Table 1 shows the detection results of norfloxacin in actual water samples by N, S-CDs.

[0093] Table 1

[0094]

[0095] As can be seen from Table 1, the recovery of norfloxacin is in the range of 90% to 104%, and the relative standard deviation (RSD) is less than 2%, indicating that N,S-CDs has high accuracy in detecting norfloxacin in actual water samples and has great practical application value.

[0096] In the above fluorescence test, the volume of the liquid to be tested for fluorescence is fixed to 1.5 mL in the cuvette using BR buffer before testing; the pH of the test environment refers to the pH of the liquid in the cuvette during the fluorescence test; when the test liquid is a simple antibiotic, the same volume of water is used to replace the antibiotic solution when F0 is obtained. The excitation light wavelength λex during the fluorescence test is 350 nm, and the excitation and emission slits are 3 nm and 1 nm, respectively.

[0097] The above is a description of the relevant contents of the present invention. A person skilled in the art will be able to implement the present invention based on these descriptions. Based on the above contents of the present invention, all other embodiments obtained by a person skilled in the art without creative work shall fall within the scope of protection of the present invention.

Claims

1. A method for detecting norfloxacin, characterized in that: Using N, S-CDs, wherein the N, S-CDs are carbon dots co-doped with nitrogen and sulfur; detecting a first fluorescence intensity of a test liquid and a second fluorescence intensity of a mixture of the test liquid and the N, S-CDs, and converting the concentration of norfloxacin in the test liquid according to a linear relationship between a ratio of the second fluorescence intensity to the first fluorescence intensity and the concentration of norfloxacin; The preparation of N,S-CDs comprises the following steps: heat-treating and purifying a mixed solution of ammonium citrate and L-cysteine ​​to obtain N,S-CDs.

2. The method for detecting norfloxacin according to claim 1, wherein: The linear relationship is: y=0.01709x+1.01243, R 2 =0.997, x is the norfloxacin concentration, x is 0.5-50 μmol / L, and y is the ratio of the second fluorescence intensity to the first fluorescence intensity.

3. The method for detecting norfloxacin according to claim 1, wherein: The pH of the test environment is 2-6; the reaction temperature of the test solution and N, S-CDs is 20-30° C.; and the reaction time of the test solution and N, S-CDs is 1-5 minutes.

4. The method for detecting norfloxacin according to claim 1, wherein: The XPS full-energy spectrum of N,S-CDs has characteristic peaks at 400.1eV, 231.1eV and 163.81eV; the XPS spectrum of N,S-CDs at N1s has characteristic peaks at 398.8eV and 400.9eV; the XPS spectrum of N,S-CDs at S2p has characteristic peaks at 164.2eV and 163.2eV.

5. The method for detecting norfloxacin according to claim 1, wherein: The FIRT spectrum of N,S-CDs is at 3432 cm -1 、3180cm -1 、1581cm -1 、1405cm -1 、1250cm -1 and 615cm -1 There are characteristic peaks.

6. A method for preparing a fluorescent detection material for detecting norfloxacin, characterized in that: The following steps are involved: (1) obtaining a mixed solution including ammonium citrate and L-cysteine; (2) heat treating the mixed liquid; (3) dispersing the heat-treated product in water and then centrifuging it; (4) The supernatant obtained by centrifugation is dialyzed to obtain an N,S-CDs aqueous solution for detecting norfloxacin.

7. The preparation method according to claim 6, characterized in that: The mass ratio of ammonium citrate to L-cysteine ​​in the mixed solution is 2-2.4, and the mixed solution is prepared by adding 0.8-1.2 g of L-cysteine ​​to every 10 mL of water.

8. The preparation method according to claim 6, characterized in that: The heat treatment temperature is 170-190° C., and the time is 60-90 min. The dialysis treatment uses a dialysis bag with a molecular weight cutoff of 1000 Da, and the dialysis time is 18-30 h.

9. The preparation method according to claim 6, characterized in that: The method also includes subjecting the mixed solution to ultrasonic treatment before the heat treatment; and filtering the supernatant obtained by the centrifugal treatment.

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