A method for detecting au (iii) and creatinine by "off-on" fluorescent sensor

Abstract

The application discloses a method for detecting Au(III) and creatinine by using a "off-on" fluorescent sensor, and belongs to the field of analysis and detection of Au(III) and creatinine. The detection method steps are as follows: (1) carbon dots are prepared by using o-phenylenediamine and isopropyl alcohol as precursors; (2) the addition of Au 3+ in the carbon dots can cause fluorescence quenching through static quenching and photoinduced electron transfer, a standard curve of Au 3+ concentration and fluorescence quenching degree is constructed, and the concentration of Au 3+ in a lake water sample is obtained; (3) creatinine is mixed with urine, and then added into the system of the carbon dots and Au 3+ , a standard curve of creatinine concentration and fluorescence recovery degree is constructed, and the concentration of creatinine in the urine sample is obtained. The application quantitatively detects Au 3+ and creatinine two substances in sequence by using a "off-on" fluorescent sensor for the first time, and the operation is simple, safe and efficient.

Description

TECHNICAL FIELD

[0001] The application relates to a method for detecting Au (III) and creatinine in a “off-on” fluorescent sensor, and belongs to the field of analysis and detection of Au (III) and creatinine. BACKGROUND

[0002] The kidney plays a vital role in filtering a large number of metabolic waste of the human body. In fact, creatinine (Cre) is a metabolic waste molecule in our muscle metabolism process. It is actually produced from creatine, which is used to generate the main energy in our muscles. Almost 2% of the precursor creatine is converted into creatinine every day, which is then transported to the kidney through the blood. When the kidney function is abnormal, the creatinine level in urine will increase. In the early stage, frequent detection of creatinine in human urine can improve the quality of life of people, especially for diabetic patients. Therefore, it is necessary to develop a simple and low-cost method for selectively and sensitively detecting creatinine in a biological sample in the early clinical diagnosis field of these diseases. In addition, with the development of modern industry, heavy metal ion pollution seriously threatens the natural environment and human health and safety, and Au 3+ ions can damage the liver, kidney and nervous system of the human body due to the strong coordination between the ions and enzymes. Therefore, it is essential to develop a method for detecting gold ions with high efficiency, sensitivity, good specificity.

[0003] In recent years, various analysis methods for detecting creatinine have been developed, mainly including high performance liquid chromatography, electrochemical method, chemiluminescence method and the like. Although these methods have high precision and reliability, they have problems such as poor selectivity, high toxicity, low sensitivity and complex operation. Therefore, it is urgent to find a simpler, faster and more sensitive Cre detection method. SUMMARY

[0004] TECHNICAL PROBLEM

[0005] The currently developed various analysis methods for detecting creatinine mainly include high performance liquid chromatography, electrochemical method, chemiluminescence method and the like. These methods have problems such as poor selectivity, high toxicity, low sensitivity and complex operation. At the same time, there are few reports on the detection of creatinine in urine by using fluorescent sensing technology, and the sensitivity and detection limit are not superior to those of traditional methods.

[0006] TECHNICAL SCHEME

[0007] A method for detecting Au 3+ and creatinine based on a “off-on” fluorescent sensor, comprising the following steps:

[0008] (1) carbon dots are synthesized by a hydrothermal method with o-phenylenediamine and isopropanol as precursors, the carbon dots are purified and diluted to obtain a carbon dot solution for subsequent detection;

[0009] (2) Prepare Au at different concentrations 3+ Standard solution, Au 3+ The standard solution was mixed thoroughly with carbon dot solution, phosphate buffer, and lake water sample, and then diluted with deionized water. After incubation, a mixed test sample solution was obtained and subjected to fluorescence spectroscopy detection.

[0010] (3) Au was measured respectively 3+ The fluorescence intensity of the mixed test sample solution with a standard solution concentration of 0 and a non-zero concentration was calculated using Au. 3+ The fluorescence quenching degree is obtained by comparing the ratio of the fluorescence intensity of the standard solution with a concentration of 0 to that of the mixed test sample solution with a concentration not equal to 0. This fluorescence quenching degree is then correlated with the Au content in the corresponding mixed test sample solution. 3+ Concentration construction of linear Au 3+ Quantitative models;

[0011] (4) Obtain the lake water sample to be tested according to step (2), detect the fluorescence intensity of the lake water sample by fluorescence spectroscopy, calculate the corresponding fluorescence quenching degree, and then, according to the linear Au in step (3) 3+ Quantitative models yield Au in lake water samples. 3+ concentration;

[0012] (5) Prepare creatinine standard solutions of different concentrations, mix the creatinine standard solutions with the urine samples, and then add carbon dot solution, phosphate buffer, and Au. 3+ The mixture of standard solutions was thoroughly mixed and diluted to volume with deionized water, then incubated to obtain a mixed urine test sample solution, which was then subjected to fluorescence spectroscopy detection.

[0013] (6) The fluorescence intensity of the mixed urine test sample solution with a concentration of creatinine standard solution that is not 0 and a concentration of 0 is measured respectively. The fluorescence recovery degree is obtained by calculating the ratio of the fluorescence intensity of the mixed test sample solution with a concentration of creatinine standard solution that is not 0 and a concentration of 0. A linear creatinine quantification model is constructed by using the fluorescence recovery degree and the corresponding creatinine concentration in the mixed urine test sample solution.

[0014] (7) Obtain the urine sample to be tested according to step (5), detect the fluorescence intensity of the urine sample to be tested by fluorescence spectroscopy, calculate the corresponding fluorescence recovery degree, and then obtain the concentration of creatinine in the urine sample to be tested according to the linear creatinine quantification model in step (6).

[0015] In one embodiment of the present invention, in step (1), the amount of o-phenylenediamine relative to isopropanol is 20-50 mg / mL; specifically, 40 mg / mL may be selected.

[0016] In an embodiment of the present application, in step (1), the o-phenylenediamine and isopropanol are added to the deionized water for hydrothermal reaction; wherein the volume ratio of isopropanol to deionized water is 1: (3-8); specifically, 1:4 can be selected.

[0017] In an embodiment of the present application, in step (1), the temperature of the hydrothermal reaction is 150-200℃, and the time is 8-15h. Specifically, 180℃ for 10h can be selected.

[0018] In an embodiment of the present application, in step (1), the synthesis process of the carbon dots is specifically as follows:

[0019] The o-phenylenediamine and isopropanol are added to the deionized water, and ultrasonic treatment is performed for 10min to make the mixture fully dissolved, and then the reaction is performed at 180℃ for 10h; wherein the amount of o-phenylenediamine relative to isopropanol is 40mg / mL, and the volume ratio of isopropanol to deionized water is 1:4.

[0020] In an embodiment of the present application, in step (1), the purification process is as follows: after the hydrothermal reaction is completed, cooling is performed to obtain a crude carbon dot solution; the crude carbon dot solution is centrifuged at 10000rpm for 10min, and then unreacted particles are removed by filtering through a microporous filter membrane with a pore size of 0.22μM, and finally the carbon dots are purified by dialysis for 12h using a dialysis membrane with a molecular weight cut-off of 1000Da to obtain the final carbon dots.

[0021] In an embodiment of the present application, in step (1), the dilution multiple of the purified carbon dots is 100-200 to obtain a carbon dot solution. Specifically, a dilution multiple of 150 can be selected.

[0022] In an embodiment of the present application, in steps (2) and (5), the fluorescence spectrum detection conditions are as follows: the fluorescence spectrum is measured by using a fluorescence spectrometer, the excitation slit and the emission slit width of the spectrometer are both 3.0nm, and the integration time is 0.1s; the excitation wavelength of the fluorescence spectrometer is 420nm, the emission wavelength range is 450nm-750nm, and the step is 1nm.

[0023] In an embodiment of the present application, in step (2), the volume ratio of the carbon dot solution, the phosphate buffer solution, the lake water sample and the different concentrations of Au 3+ standard solution is 1:1:1:1.

[0024] In an embodiment of the present application, in step (2), the constant volume condition is that the volume ratio of the constant volume to the Au 3+ standard solution is 10:1.

[0025] In an embodiment of the present application, in step (2), the incubation time is 1-20min; specifically, 5min can be selected.

[0026] In an embodiment of the present application, the linear Au 3+ The quantitative model is:

[0027] F0 / F=1.0582c(Au 3+ )-4.5696, wherein F0 and F respectively represent the fluorescence intensity of the mixed test sample liquid with the concentration of Au 3+ standard solution being 0 and not being 0, and c(Au 3+ ) represents the concentration of Au 3+ in the mixed test sample liquid.

[0028] In an embodiment of the present application, the volume ratio of the sample to be tested and the carbon dot solution in step (4) is 1:1.

[0029] In an embodiment of the present application, the concentration of the Au 3+ standard solution in step (5) is fixed at 10 μmol / L.

[0030] In an embodiment of the present application, in step (5), the volume ratio of the carbon dot solution, the phosphate buffer solution, the lake water sample and the Au 3+ standard solution with different concentrations is 1:1:1:1.

[0031] In an embodiment of the present application, in step (5), the constant volume condition is that the ratio of the volume after constant volume to the volume of the Au 3+ standard solution is 10:1.

[0032] In an embodiment of the present application, in step (5), the incubation time is 1-20 min.

[0033] In an embodiment of the present application, the linear creatinine quantitative model in step (6) is: F / F1=1.8536c(Cre)+1.1356, wherein F1 and F respectively represent the fluorescence intensity of the mixed urine test sample liquid with the concentration of the creatinine standard solution being 0 and not being 0, and c(Cre) represents the concentration of creatinine in the mixed urine test sample liquid.

[0034] The present application also provides the application of the above detection method in the field of biomedical detection.

[0035] Beneficial effects:

[0036] The present application applies the "on-off" type fluorescent sensor to the detection of Au 3+ and creatinine, and the carbon dots are spherical or spherical-like in appearance and contain rich functional groups on the surface, thereby improving the water solubility of the carbon dots and the binding capacity of the carbon dots with Au 3+ .

[0037] The present application first uses o-phenylenediamine and isopropanol as raw materials to synthesize carbon dots as a fluorescent sensor to realize the quantitative detection of Au 3+ and creatinine in urine, and the method is simple, fast, safe and suitable for routine analysis. The Au 3+ interacts with the functional groups on the surface of the carbon dots and causes fluorescence quenching by electron transfer, and there is also static quenching. 3+ The present application has high selectivity, the creatinine molecules have strong binding capacity with the reduced gold nanoparticles, and then the fluorescence is recovered. 3+ The sensor can detect Au 3+ and creatinine in the same system in sequence.

[0038] The present application detects Au 3+ in the linear range of 8-12 μmol / L, and the detection limit is as low as 1.69*10 -8 mol / L; the linear range of creatinine detection is 0.05-1 μmol / L, and the detection limit is 9.29*10 -9 mol / L, which has important significance for environmental monitoring and biomedical field. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The flow chart for detecting Au 3+ and creatinine by using the "off-on" type fluorescent sensor.

[0040] Figure 2 The fluorescence spectrum diagram when different concentrations of Au 3+ are added in the system in Example 1.

[0041] Figure 3 The relationship curve between the fluorescence quenching degree and the concentration of Au 3+ in Example 1.

[0042] Figure 4 The linear fitting curve between the fluorescence quenching degree and the concentration of Au 3+ in the range of 8-12 μM in Example 1.

[0043] Figure 5 The fluorescence spectrum diagram when different concentrations of creatinine are added in the system in Example 2.

[0044] Figure 6 The relationship curve between the fluorescence recovery degree and the concentration of creatinine in Example 2.

[0045] Figure 7 The linear fitting curve between the fluorescence recovery degree and the concentration of creatinine in the range of 0.05-1 μM in Example 2.

[0046] Figure 8 The detection of Au3+ Graph of selective test results.

[0047] Figure 9 Graph of selective test results for detecting creatinine in Example 4.

[0048] Figure 10 Graph of Au 3+ concentration influence test results for detecting creatinine in Example 5. DETAILED DESCRIPTION

[0049] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application.

[0050] Example 1 Preparation of carbon dot (CD) solution

[0051] 0.2 g of o-phenylenediamine and 5 mL of isopropyl alcohol were weighed in a beaker, 20 mL of deionized water was added, and the mixture was ultrasonically treated for 10 min to fully dissolve the mixture, and then reacted at 180℃ for 10 h, and cooled to obtain a crude carbon dot solution. The crude carbon dot solution was centrifuged at 10000 rpm for 10 min, and the supernatant was collected, and then filtered through a 0.22 μM microporous filter to remove unreacted particles, and finally the carbon dots were purified by dialysis for 12 h using a dialysis membrane with a molecular weight cut-off of 1000 Da to obtain the final carbon dots. The carbon dot solution for subsequent experiments was based on this.

[0052] Example 2 Construction of Au 3+ linear assay model

[0053] (1) Preparation of sample solution: carbon dot solution (diluted 150 times from the carbon dots obtained in Example 1), phosphate buffer (pH = 8), lake water sample, and Au 3+ standard solution with concentrations of 0 (blank control), 1 μM, 2 μM, 3 μM, 4 μM, 5 μM, 6 μM, 7 μM, 8 μM, 9 μM, 9.5 μM, 10 μM, 11 μM, 11.5 μM, 12 μM, 13 μM, 14 μM, 15 μM, respectively;

[0054] (2) The four substances were mixed, and the volume of the carbon dot solution, the phosphate buffer, the lake water sample, and the Au 3+ standard solution with different concentrations were all 0.3 mL, and then deionized water was added to a constant volume of 3 mL, and incubated for 5 min to obtain mixed test sample solutions with different Au 3+ concentrations, and fluorescence spectrum detection was performed, and the reaction temperature was 20℃;

[0055] (3) Determination of the fluorescence spectrum of the system: Scanning conditions: excitation wavelength 420 nm, emission wavelength scanning range 450-750 nm, scanning once every 1 nm, slit width set to 3.0 nm / 3.0 nm (excitation slit / emission slit), obtaining the fluorescence intensity peak F at 420 nm. Figure 2 Add Au 3+ Fluorescence spectroscopy was performed on the mixed test sample solution with a concentration of 0, and the fluorescence intensity peak F0 at 570 nm was obtained. The fluorescence quenching degree F0 / F was recorded.

[0056] (4) Plot the fluorescence quenching degree of the sample solution against the Au content in the mixed test sample solution. 3+ Concentration relationship curve, such as Figure 3 As shown, the degree of quenching and Au 3+ The fitted curve is as follows Figure 4 ,from Figure 3 , Figure 4 It can be seen that when Au 3+ At concentrations of 8-12 μM, the degree of fluorescence quenching in the solution is related to Au. 3+ The concentration shows a linear relationship, with the linear equation being F0 / F = 1.0582c(Au). 3+ The correlation coefficient is -4.5696, and the correlation coefficient is R. 2 =0.9911, detection limit is 1.69×10 -8 mol / L.

[0057] Example 3: Constructing a linear measurement model for creatinine

[0058] (1) Preparation of sample solutions: carbon dot solution (diluted 150 times), phosphate buffer (pH=8), Au 3+ Standard solution (10 μM), urine sample, and standard solutions of creatinine with concentrations of 0 (blank control), 0.05 μM, 0.1 μM, 0.2 μM, 0.3 μM, 0.4 μM, 0.5 μM, 0.7 μM, 0.8 μM, 1 μM, 1.5 μM, and 2 μM, respectively;

[0059] (2) First, prepare the carbon dot solution, phosphate buffer, and Au. 3+ The standard solutions were mixed evenly, with each of the three solutions having a volume of 0.3 mL. Then, urine solutions of different concentrations of creatinine (creatinine and urine each having a volume of 0.3 mL) were added. Finally, the volume was adjusted to 3 mL with deionized water and incubated for 20 min to obtain mixed urine test sample solutions spiked with different creatinine concentrations. Fluorescence spectroscopy was then performed to detect the samples.

[0060] (3) Fluorescence spectrum of the determination system: scanning conditions and detection of Au 3+To keep consistency, the sample solution with 0 concentration of creatinine was added to detect the fluorescence spectrum, and the fluorescence intensity peak F1 at 570 nm was obtained. The mixed urine test sample solution with other concentrations of creatinine standard solution was added to obtain the fluorescence intensity peak F, and the fluorescence recovery degree F / F1 was recorded, as shown in Figure 5 .

[0061] (5) The relationship curve between the fluorescence recovery degree of the sample solution and the creatinine concentration in the mixed urine test sample was drawn, as shown in Figure 6 . The fitting curve of the recovery degree and creatinine is as shown in Figure 7 . From Figure 6 , Figure 7 it can be seen that when the creatinine concentration is 0.05-1 μM, the fluorescence recovery degree of the solution is linearly related to the creatinine concentration, the linear equation is F / F1=1.8536c(Cre)+1.1356, the correlation coefficient is R 2 =0.9965, and the detection limit is 9.29×10 -9 mol / L.

[0062] Example 4: Investigation of the selectivity of the fluorescence "off" process for detecting Au 3+

[0063] Referring to Example 2, 12 different common metal ions (Na + , K + , Ca 2+ , Mg 2+ , Al 3+ , Cu 2+ , Fe 3+ , Zn 2+ , Hg 2+ , Pb 2+ , Ag + ) were selected as interference substances, as shown in Figure 8 , F0 and F represent the fluorescence intensities before and after the addition of metal ions, respectively. The concentration of all cations was 12 μM, and all fluorescence detections were performed under the same conditions.

[0064] According to the detection results, the interference substances have no obvious fluorescence quenching effect on the carbon dots, and will not interfere with the detection of Au 3+ ions.

[0065] Example 5: Investigation of the selectivity of the fluorescence "on" process for detecting creatinine

[0066] Referring to Example 3, eight common organic substances and inorganic salt ions in urine (urea, uric acid, glucose, ascorbic acid, dopamine, histidine, Cl - , NO3 - ) were selected as interference substances to study CDs-Au 3+ ​The selectivity of the system for detecting creatinine was measured with the concentration of creatinine and interferents both being 10 μM, Au 3+ The detection results are shown in Table 1. Figure 9

[0067] According to the images, creatinine has a significant restoring effect on the fluorescence of CDs-Au 3+ system, and other substances cannot basically restore the fluorescence.

[0068] Example 6: Influence of Au 3+ concentration on the detection of creatinine

[0069] Referring to Example 3, Au 3+ standard solutions with different concentrations (8 μM, 9 μM, 10 μM, 11 μM, 12 μM) were added to the carbon dot solution, and the concentration of creatinine was controlled to be 0.5 μM in order to maximize the sensitivity of the detection of creatinine. The measured results are shown in Table 1. Figure 10 When the concentration of Au 3+ is 10 μM, the fluorescence recovery effect is slightly obvious, and therefore, the concentration of Au 3+ is fixed at 10 μM when detecting creatinine.

[0070] Example 7: Detection of Au 3+

[0071] Referring to Example 2, Au 3+ with concentrations of 8, 9, and 10 μM was measured, and the detection results are shown in Table 1.

[0072] Table 1: Test results of Example 7

[0073] Spiked concentration (μΜ) Detection concentration (μΜ) Recovery (%) Relative standard deviation (%), n = 3 8 8.06 100.7 0.33 9 8.97 99.7 0.31 10 10.06 100.6 0.58

[0074] Example 8: Detection of creatinine in urine

[0075] Referring to Example 3, creatinine with concentrations of 100, 300, and 500 nM was measured, and the detection results are shown in Table 2. The detection results are satisfactory, indicating that this method is accurate and feasible, and can be applied to the biomedical field to detect creatinine.

[0076] Table 2: Test results of Example 8

[0077] Spiked concentration (nM) Detection concentration (nM) Recovery (%) Relative standard deviation (%), n = 3 100 101 101.0 0.79 300 292 97.3 0.75 500 527 105.4 2.11

[0078] Comparative Example 1: Comparison of other fluorescence methods for detecting creatinine in existing reports

[0079] ​In a prior report (Label-free detection of creatinine using nitrogen passivated fluorescent carbon dots. RSC Adv. 2020, 10, 36253), carbon dots were synthesized using ascorbic acid and urea, thiourea, and cysteine as raw materials, and then modified with picric acid, which is an explosive and controlled product, and is not suitable as a synthetic material.

[0080] Meanwhile, there is also a report (A copper nanoclusters probe for dual detection of microalbumin and Creatinine. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. 2022, 270, 120816) using copper nanoclusters to detect creatinine, but the detection limit of this method is only 1.3 x 10 -5 M, and has no advantage for the detection of trace creatinine. Therefore, the method of the present application has the advantages of rapid preparation, sensitive detection, and low cost.

[0081] Preparation of carbon dots with different carbon sources and o-phenylenediamine in Comparative Example 2

[0082] 0.2 g of o-phenylenediamine and 5 mL of glycerol were weighed into a beaker, 20 mL of deionized water was added, and the mixture was ultrasonically treated for 10 min to fully dissolve the mixture, and then reacted at 180℃ for 10 h. The synthesized crude carbon dot solution was centrifuged at 10000 rpm for 10 min, and then filtered through a 0.22 μM microporous filter to remove unreacted particles, and finally purified by dialysis membrane with a molecular weight cut-off of 1000 Da for 12 h to obtain the final carbon dots.

[0083] The carbon dots obtained in Example 1 and Comparative Example 2 were each diluted 150 times and subjected to fluorescence spectrum detection under excitation light at a wavelength of 420 nm. The fluorescence peak positions of the two were different. 0.3 mL of each of the two kinds of carbon dots was taken into a test tube, 0.3 mL of 10 μM Au 3+ solution, 0.3 mL of 1 μM Cre solution, and deionized water were added to make up to 3 mL, and incubated for 3 min before fluorescence spectrum detection. The fluorescence quenching rate and fluorescence recovery rate in the carbon dot system obtained in Example 1 were higher than those in Comparative Example 2.

[0084] Although the present application has been disclosed with reference to the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make various modifications and modifications without departing from the spirit and scope of the present application, and therefore the protection scope of the present application should be defined by the claims.

Claims

1. A method for detecting Au based on an "off-on" type fluorescence sensor 3+ The method for controlling creatinine includes the following steps: (1) Carbon dots were synthesized by hydrothermal method using o-phenylenediamine and isopropanol as precursors. After purification and dilution, carbon dot solution was obtained for subsequent detection. (2) Prepare Au at different concentrations 3+ Standard solution, Au 3+ The standard solution was mixed thoroughly with carbon dot solution, phosphate buffer, and lake water sample, and then diluted with deionized water. After incubation, a mixed test sample solution was obtained and subjected to fluorescence spectroscopy detection. (3) Au was measured respectively 3+ The fluorescence intensity of the mixed test sample solution with a standard solution concentration of 0 and a non-zero concentration was calculated using Au. 3+ The fluorescence quenching degree is obtained by comparing the ratio of the fluorescence intensity of the standard solution with a concentration of 0 to that of the mixed test sample solution with a concentration not equal to 0. The fluorescence quenching degree is then correlated with the Au content in the corresponding mixed test sample solution. 3+ Concentration construction of linear Au 3+ Quantitative models; (4) Obtain the lake water sample to be tested according to step (2), detect the fluorescence intensity of the lake water sample by fluorescence spectroscopy, calculate the corresponding fluorescence quenching degree, and then, according to the linear Au in step (3) 3+ Quantitative models yield Au in lake water samples. 3+ concentration; (5) Prepare creatinine standard solutions of different concentrations, mix the creatinine standard solutions with the urine samples, and then add carbon dot solution, phosphate buffer, and Au. 3+ The mixture of standard solutions was thoroughly mixed and diluted to volume with deionized water, then incubated to obtain a mixed urine test sample solution, which was then subjected to fluorescence spectroscopy detection. (6) The fluorescence intensity of the mixed urine test sample solution with a concentration of creatinine standard solution that is not 0 and a concentration of 0 is measured respectively. The fluorescence recovery degree is obtained by calculating the ratio of the fluorescence intensity of the mixed test sample solution with a concentration of creatinine standard solution that is not 0 and a concentration of 0. A linear creatinine quantification model is constructed by using the fluorescence recovery degree and the corresponding creatinine concentration in the mixed urine test sample solution. (7) Obtain the urine sample to be tested according to step (5), detect the fluorescence intensity of the urine sample to be tested by fluorescence spectroscopy, calculate the corresponding fluorescence recovery degree, and then obtain the concentration of creatinine in the urine sample to be tested according to the linear creatinine quantification model in step (6).

2. The method according to claim 1, characterized in that, In step (1), the amount of o-phenylenediamine relative to isopropanol is 20-50 mg / mL.

3. The method according to claim 1, characterized in that, In step (1), o-phenylenediamine and isopropanol are added to deionized water for a hydrothermal reaction; wherein the volume ratio of isopropanol to deionized water is 1:(3-8).

4. The method according to claim 3, characterized in that, In step (1), the hydrothermal reaction temperature is 150-200℃ and the time is 8-15h.

5. The method according to claim 1, characterized in that, In step (1), the purified carbon dots are diluted 100-200 times to obtain a carbon dot solution.

6. The method according to claim 1, characterized in that, In step (2), carbon dot solution, phosphate buffer, lake water sample, and Au at different concentrations were used. 3+ The volume ratio of the standard solutions is 1:1:1:

1.

7. The method according to claim 1, characterized in that, In step (2), the condition for volume determination is: the volume after volume determination is equal to the volume of Au. 3+ The volume ratio of the standard solution is 10:1; the incubation time is 1-20 min.

8. The method according to claim 1, characterized in that, In step (5), Au 3+ The concentration of the standard solution was fixed at 10 μmol / L.

9. The method according to claim 1, characterized in that, In step (5), carbon dot solution, phosphate buffer, lake water sample, and Au at different concentrations are used. 3+ The volume ratio of the standard solutions is 1:1:1:1; the conditions for making up to volume are: the volume after making up to volume and the volume of Au... 3+ The volume ratio of the standard solution is 10:1; the incubation time is 1-20 min.

10. The method according to any one of claims 1-9, characterized in that, The conditions for fluorescence spectroscopy detection in steps (2) and (5) are as follows: the fluorescence spectrum is measured using a fluorescence spectrometer, the excitation slit and emission slit width of the spectrometer are both 3.0 nm, the integration time is 0.1 s; the excitation wavelength of the fluorescence spectrometer is 420 nm, the emission wavelength range is 450 nm-750 nm, and the step size is 1 nm.

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