Preparation method and application of lignin-based nitrogen-doped carbon dots with photoresponse simulated oxidase activity and green fluorescence
The lignin-based nitrogen-doped carbon dots with photoresponsive simulated oxidase activity and green fluorescence were prepared by hydrothermal method, which solved the problem of poor activity of existing carbon dots under visible light and difficult to regulate the fluorescence wavelength, and achieved high accuracy and anti-interference nitrite detection.
Patent Information
- Application Number
- CN202510384277.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2025-07-01
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a preparation method and application of lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence, belonging to the technical fields of nanomaterial preparation and nitrite detection. Background Art
[0002] Nitrite is a food additive commonly used for meat preservation. However, excessive nitrite can be harmful to the human body, such as interfering with oxygen transport, causing teratogenesis, carcinogenesis, etc. Therefore, it is very important to establish a detection method for nitrite. Currently, existing detection methods, such as ion chromatography, Griess reagent, fluorescence method or colorimetric method, etc., have problems such as high detection cost, complex operation or being easily interfered by the environment. Therefore, it is necessary to develop a sensing system for multi-signal detection to improve the accuracy and anti-interference ability of nitrite detection. Carbon dots have excellent fluorescence properties, and their applications in the field of sensing detection have been widely explored. In order to expand the detection ability and scope, while the fluorescence properties of carbon dots have been deeply studied, a photo-responsive mimetic oxidase activity has also been developed. Therefore, multi-mode detection can be achieved based on the fluorescence properties and mimetic oxidase activity of carbon dots.
[0003] High-performance visible-light-responsive mimetic oxidases usually have a lower energy gap structure, which makes electrons more easily excited by visible light, thereby promoting the separation of electrons and holes to catalyze the formation of free radicals. Currently, most carbon dots mainly absorb ultraviolet light and have poor mimetic enzyme activity under visible light irradiation. The size effect (larger size) and heteroatom (O, N, S, P, etc.) doping means can be used to adjust the structure of carbon dots to solve the above problems. The above two means can also synchronously improve the fluorescence properties of carbon dots, improve their quantum efficiency or shift the emission wavelength to the red. Based on the fluorescence properties and enzyme activity of carbon dots during the detection of nitrite, a medium 3,3',5,5'-tetramethylbenzidine (TMB) that can be oxidized by free radicals to turn blue needs to be introduced. However, the above-reported carbon dots only emit blue fluorescence, and the oxidized TMB itself can emit purple fluorescence, which will interfere with the detection effect of blue fluorescence. Therefore, it is necessary to improve the photo-responsive mimetic enzyme activity of carbon dots and promote the red shift of the fluorescence emission wavelength through structural design.
[0004] Lignin is the only natural polymer containing a benzene ring structure in nature and is considered a potential precursor to promote the sustainable development of carbon materials. In addition, during the synthesis of carbon dots, using substances with a benzene ring structure as a carbon source or dopant is one of the strategies to regulate size increase. However, due to its large molecular weight, high steric hindrance, and heterogeneous structure, lignin has poor reactivity. Therefore, preparing high-performance lignin-based carbon dots usually requires pretreatment of lignin such as fractionation, modification, and oxidation to improve its reactivity. However, the processes of lignin fractionation, modification, and oxidation are complex and require precise control of conditions to avoid over-degradation or incomplete reaction, which increases the difficulty of industrial production. Therefore, it is necessary to develop simpler and more environmentally friendly treatment methods to achieve the high-value utilization of lignin Summary of the Invention
[0005] The object of the present invention is to provide a preparation method and application of lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence. In the present invention, kraft lignin is used as a carbon source, m-phenylenediamine is used as a nitrogen dopant, and concentrated nitric acid is used as an oxidant. Carbon dots with both photoluminescence properties and mimetic oxidase activity are prepared by a hydrothermal method, solving the problems of low visible light absorption ability and difficult fluorescence wavelength regulation of carbon dots; then it is used for colorimetric-ratio-fluorescence "multi-mode" sensing detection of nitrite, solving the problems of single detection mode of nitrite and susceptibility to detection environment interference. At the same time, in the preparation process of the present invention, there is no need to pretreat kraft lignin, the process is simple, green and environmentally friendly, the equipment is simple, and the raw material cost is low, which is conducive to large-scale industrial production.
[0006] A preparation method of lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence, dissolving kraft lignin, m-phenylenediamine, and concentrated nitric acid in deionized water, stirring evenly, and performing a hydrothermal reaction at 200 °C for 24 h to obtain lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence, wherein the concentration of the kraft lignin is 10 mg / mL, the mass ratio of m-phenylenediamine to kraft lignin is 1:1, and the volume ratio of concentrated nitric acid to deionized water is 5-20 μL:1 mL.
[0007] Further, the concentrated nitric acid is commercially available concentrated nitric acid with a mass fraction of about 68%.
[0008] Further, when the dosage of the concentrated nitric acid increases from 5 μL / mL to 10 μL / mL, the photo-responsive mimetic oxidase activity and fluorescence intensity of the obtained carbon dots gradually increase; when it increases from 10 μL / mL to 20 μL / mL, the photo-responsive mimetic oxidase activity and fluorescence intensity of the obtained carbon dots gradually decrease.
[0009] Preferably, the volume ratio of concentrated nitric acid to deionized water is 10 μL:1 mL.
[0010] A preferred technical solution of the present invention includes the following steps: At room temperature, sulfate lignin, m-phenylenediamine, and concentrated nitric acid are dissolved in deionized water, stirred and mixed evenly to obtain a brownish-yellow solution; the obtained dark brown solution is transferred to a high-pressure reactor, sealed, placed in a magnetic stirrer, stirred evenly, and then subjected to a hydrothermal reaction at 200 °C for 24 h. After the reaction is completed, it is cooled to room temperature to obtain a dark brown reaction solution; the obtained reaction solution is subjected to ultrasonic treatment, centrifugation, and filtration, and the filtrate obtained by filtration is dialyzed with deionized water to obtain a solid product, which is dried to obtain lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence.
[0011] In the above technical solution, the ultrasonic condition is ultrasonic dispersion for 20 min in a ultrasonic cell disruptor under the condition of ultrasonic dispersion for 2 s and stopping for 3 s at a power of 100 W.
[0012] In the above technical solution, the centrifugation condition is centrifugation at 5000 rpm for 5 min.
[0013] In the above technical solution, the filtration method is to use a 0.22 μm aqueous filter membrane to filter out insoluble precipitates in the solution to obtain a clear liquid.
[0014] In the above technical solution, the dialysis condition is to purify the filtrate using a cellulose ester dialysis bag with a molecular weight cut-off of 1000 Da. The dialysis treatment time is 48 h, and the water is changed every 8 - 12 h.
[0015] In the above technical solution, the drying condition is drying at 60 °C for 24 h in a forced-air drying oven.
[0016] Another object of the present invention is to provide lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence prepared by the above method.
[0017] Further, the lignin-based nitrogen-doped carbon dots are spherical nanoparticles with an average particle size of 1.25 - 1.75 nm.
[0018] Further, the optimal excitation wavelength and optimal emission wavelength of the lignin-based nitrogen-doped carbon dots change with the amount of concentrated nitric acid used. When the amount of concentrated nitric acid used increases from 5 μL / mL to 20 μL / mL, the optimal excitation wavelength range of the obtained carbon dots is 425 - 445 nm, and the optimal emission wavelength range is 495 - 515 nm.
[0019] Further preferably, when the amount of concentrated nitric acid used is 10 μL / mL, the optimal excitation wavelength of the obtained carbon dots is 445 nm, and the optimal emission wavelength is 515 nm.
[0020] Furthermore, the lignin-based nitrogen-doped carbon dots have photoluminescence and mimetic oxidase activity, and their catalytic ability can be activated by visible light irradiation during use.
[0021] Another object of the present invention is to provide the application of the above-mentioned lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence in the detection of nitrite.
[0022] Furthermore, the lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence can simultaneously achieve multi-mode detection of nitrite by colorimetry, ratio method, and fluorescence method.
[0023] A nitrite colorimetric-ratio-fluorescence multi-mode detection method based on the above-mentioned lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence includes the following steps: Mix an aqueous solution of carbon dots, an ethanol solution of 3,3',5,5'-tetramethylbenzidine, and an acetic acid-sodium acetate buffer solution with a pH of 4, and irradiate with an EDL flashlight with a light power density of 15 mW / m 2 for 10 min, then add the test sample solution containing nitrite and continue to incubate for 15 min, observe the color change of the solution, measure the absorbance and fluorescence intensity, and achieve multi-mode detection of nitrite by colorimetry, ratio method, and fluorescence method.
[0024] Furthermore, after incubation of the above mixed solution, the color, absorbance, and fluorescence intensity of the solution can change simultaneously, and thus it is possible to simultaneously detect nitrite by colorimetry, ratio method, and fluorescence method.
[0025] In the above technical solution, the volume ratio of the carbon dot solution, the ethanol solution of 3,3',5,5'-tetramethylbenzidine, the acetic acid-sodium acetate buffer solution, and the test sample solution containing nitrite is 48:56:1862:35.
[0026] Furthermore, the concentration of the aqueous solution of carbon dots is 1 mg / mL, and the concentration of the ethanol solution of 3,3',5,5'-tetramethylbenzidine is 5 mM.
[0027] Even further, the detection range of the colorimetry method is 0-250 μM, and the color gradually changes from blue to green and then to yellow as the nitrite concentration increases.
[0028] Even further, the detection range of the ratio method is 0-250 μM, and the detection limit is 0.85 μM.
[0029] Even further, the detection range of the fluorescence method is 0-250 μM, and the detection limit is 1.06 μM.
[0030] The lignin-based nitrogen-doped carbon dots with photo-responsive mimetic oxidase activity and green fluorescence in the present invention have strong absorption capacity for visible light, which not only improves the mimetic oxidase activity of the carbon dots under visible light irradiation, but also realizes the regulation of the fluorescence wavelength of the carbon dots, shifting the optimal emission wavelength of the carbon dots to the green light region. At the same time, the green fluorescence of the carbon dots in the present invention enables them to overcome the interference of the purple fluorescence emitted by TMB itself after oxidation when detecting nitrite, with high fluorescence color recognition and more sensitive and accurate detection results.
[0031] The nitrite detection method in the present invention uses the carbon dots + TMB mixed solution system obtained in the present invention. This system can reduce dissolved oxygen to superoxide anion radicals after visible light irradiation, and the superoxide anion radicals can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to TMB + , turning the solution blue and having absorption at the visible light wavelength of 652 nm. Then the oxidized TMB + can undergo a diazotization reaction with nitrite to change the solution from blue to green, and gradually from green to yellow as the concentration of nitrite increases, realizing the visual detection of nitrite; TMB + The diazotization product formed by TMB and nitrite has an absorbance at 445 nm, and the ratio of the absorbances at 652 nm and 445 nm (A652 / A445) has a linear relationship with the concentration of nitrite; TMB + The diazotization product formed by TMB and nitrite can quench the fluorescence of the carbon dots, and the fluorescence intensity has a linear relationship with the concentration of nitrite.
[0032] The beneficial effects of the present invention:
[0033] (1) The present invention uses the most common sulfate lignin in industrial production as a carbon source to prepare carbon dots. Sulfate lignin not only has rich reserves in nature, but can also be extracted from non-food waste biomass, avoiding the problems of high cost and difficulty in obtaining carbon source materials. At the same time, the present invention adopts a one-step hydrothermal method to prepare carbon dots without pretreatment of lignin, with a simple and convenient method, which is conducive to large-scale industrial production.
[0034] (2) The carbon dots obtained in the present invention have photo-responsive mimetic oxidase activity and show excellent TMB catalytic ability under visible light irradiation. They can form a solution system with TMB and buffer solution for the detection of various substances such as nitrite, glutathione, and dopamine. At the same time, the carbon dots obtained in the present invention can emit green fluorescence with high color recognition. In addition to being used for sensing detection, they can also be used for fluorescence anti-counterfeiting.
[0035] (3) The carbon dots obtained in the present invention can achieve colorimetric-ratio-fluorescent multimode detection of nitrite. Among them, the detection ranges of colorimetry, ratio method, and fluorescence method are all 0-250 μM. The detection limit of the ratio method is 0.85 μM, and the detection limit of the fluorescence method is 1.06 μM. At the same time, the bright green fluorescence emitted by it avoids the purple fluorescence interference of oxidized TMB, making the detection effect more sensitive and the detection result more accurate. Description of the Drawings
[0036] Figure 1 It is the transmission electron microscope image (a) and particle size distribution diagram (b) of the carbon dots obtained in Example 2.
[0037] Figure 2 It is the ultraviolet-visible absorption spectrum diagram (a) and fluorescence excitation-emission spectrum diagram (b) of the carbon dots obtained in Example 2.
[0038] Figure 3 (a) is the catalytic activity of the carbon dots obtained in Example 2 on TMB at different concentrations, Figure 3 (b) is the fluorescence and color diagram of the solution after the carbon dots obtained in Example 2 catalyze TMB at different concentrations, Figure 3 (c) is the catalytic activity diagram of the carbon dots obtained in Example 2 on different concentrations of TMB, Figure 3 (d) is the fluorescence and color diagram of the solution after the carbon dots obtained in Example 2 catalyze different concentrations of TMB.
[0039] Figure 4 It is the EPR spectrum diagram of the carbon dots obtained in Example 2.
[0040] Figure 5 It is the detection result diagram of the carbon dots obtained in Example 2 for nitrite. Among them, (a) is the ultraviolet-visible absorption spectrum diagram of the carbon dot + TMB system responding to different concentrations of nitrite; (b) is the linear relationship diagram between the A652 / A445 value and the nitrite concentration; (c) is the fluorescence spectrum diagram of the carbon dot + TMB system responding to different concentrations of nitrite; (d) is the linear relationship diagram between the F0 / F value and the nitrite concentration. Detailed Embodiments
[0041] The following non-limiting embodiments can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.
[0042] In the following embodiments, the test methods are all conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial channels unless otherwise specified.
[0043] Example 1
[0044] A preparation method of carbon dots with light-responsive mimetic oxidase activity and green fluorescence, including the following steps:
[0045] 500 mg of softwood kraft lignin, 500 mg of m-phenylenediamine and 250 μL of concentrated nitric acid were added to a beaker containing 50 mL of ultrapure water, stirred with a magnetic stirrer until evenly mixed, and then transferred to a 100 mL poly(p-xylylene) (PPL) liner; after sealing the liner with a stainless steel autoclave, it was heated using a magnetic stirrer equipped with a heating module, the hydrothermal reaction temperature was 200 °C, and the reaction time was 24 h; after the reaction ended and the autoclave cooled to room temperature, the obtained dark brown reaction solution was ultrasonically dispersed for 20 min using an ultrasonic cell disruptor under the conditions of ultrasonic dispersion at 100 W for 2 s and stopping for 3 s, and then the solution was transferred to a 50 mL centrifuge tube and centrifuged at 5000 rpm for 5 min; the supernatant after centrifugation was collected, filtered through a 0.22 μm pinhole aqueous filter membrane, and then the filtrate was injected into a 1000 Da dialysis bag for purification treatment for 48 h, changing the water every 8 - 12 h, and finally the dialyzed solution was dried in a blast drying oven to obtain pure carbon dots.
[0046] The carbon dots obtained above were prepared into an aqueous carbon dot solution with a concentration of 1 mg / mL using deionized water. 48 μL of the aqueous carbon dot solution and 56 μL of a 3,3',5,5'-tetramethylbenzidine ethanol solution (concentration 5 mM) were added to 1896 μL of an acetic acid - sodium acetate (pH = 4) buffer solution, and irradiated with an EDL flashlight with a light power density of 15 mW / m 2 for 10 min, and then the absorbance of the mixed solution at 652 nm was measured, and the result was 0.311. Among them, the magnitude of the absorbance value reflects the strength of the carbon dot mimicking oxidase activity.
[0047] Example 2
[0048] Referring to Example 1, the difference from Example 1 was that the concentrated nitric acid was 500 μL. The absorbance of the carbon dots prepared under this condition and the TMB ethanol mixed solution at 652 nm after illumination was 0.521.
[0049] Example 3
[0050] Referring to Example 1, the difference from Example 1 was that the concentration of concentrated nitric acid was 1000 μL. The absorbance of the carbon dots prepared under this condition and the TMB ethanol mixed solution at 652 nm after illumination was 0.06.
[0051] Result analysis:
[0052] Figure 1 Figure 26 shows the transmission electron microscope image and particle size distribution diagram of the carbon dots obtained in Example 2. It can be seen from the figure that the carbon dots are spherical nanoparticles with an average particle size of about 1.25 - 1.75 nm.
[0053] Figure 2 The UV-Vis absorption spectrum and fluorescence excitation-emission spectrum of the carbon dots obtained in Example 2. Figure 2 (a) shows that the carbon dots have obvious absorption in the visible light range of 400-500 nm; Figure 2 (b) shows that the optimal excitation wavelength of the carbon dots is 445 nm and the optimal emission wavelength is 515 nm.
[0054] Figure 3 The fluorescence and color change diagrams of the carbon dots + TMB system solution in the presence of different concentrations of carbon dots (obtained in Example 2) and different TMB concentrations. From Figure 3 (a), it can be seen that the catalytic activity of the carbon dots towards TMB increases with the increase of the carbon dot concentration. When the carbon dot concentration exceeds 24 μg / mL, the increasing trend of the catalytic activity slows down. At the same time, the increase of the carbon dot concentration makes the fluorescence of the solution continuously enhance and the color of the solution gradually deepen ( Figure 3 (b)). From Figure 3 (c), it can be seen that with the increase of the TMB concentration, the absorbance of the solution continuously enhances, indicating that the carbon dots have excellent catalytic ability. Figure 3 (d) is the diagram of the fluorescence and color of the solution changing with the TMB concentration. It can be seen that: the higher the TMB concentration, the deeper the color of the solution, but when the TMB concentration exceeds 56 μM, the color of the solution will cause fluorescence quenching.
[0055] Figure 4 The EPR spectrum of the carbon dots obtained in Example 2. During the test, DMPO was used as a scavenger for superoxide anion radicals. Under light illumination, when no carbon dots were introduced, no radicals were captured by DMPO; when carbon dots were introduced, typical signals corresponding to superoxide anion radicals appeared, indicating that the principle of the carbon dots in this invention catalyzing the color change of TMB is to convert dissolved oxygen into superoxide anion radicals, and then the radicals rob the electrons of TMB to oxidize it to blue.
[0056] Figure 5 The effect diagram of the sensing system constructed with the carbon dots obtained in Example 2 assisted by TMB for the detection of nitrite. The construction method of the sensing system is as follows: The carbon dots are prepared into an aqueous carbon dot solution with a concentration of 1 mg / mL using deionized water. Take 48 μL of the carbon dot solution and 56 μL of 3,3',5,5'-tetramethylbenzidine ethanol solution (concentration of 5 mM) and add them to 1862 μL of acetic acid-sodium acetate (pH = 4) buffer solution. After irradiating with an EDL flashlight with a light power density of 15 mW / m 2 for 10 min, add 35 μL of sodium nitrite solutions with different concentrations (0-250 μM) and continue to incubate for 15 min. Observe the color change, and then the obtained solutions are respectively detected for fluorescence intensity using a fluorescence spectrophotometer and absorbance using an ultraviolet-visible spectrophotometer. From Figure 5It can be seen from (a) that when the concentration of nitrite increases, the absorbance of the carbon dots + TMB system at 445 nm increases rapidly, while the absorbance at 652 nm decreases. Figure 5 (b) shows that the standard curve of the absorbance ratio of 652 nm to 445 nm and the concentration of nitrite is linearly related, with a detection range of 0 - 250 μM and a detection limit of 0.85 μM. From Figure 5 (c), it can be seen that as the concentration of nitrite increases, the fluorescence intensity of the carbon dots + TMB system gradually decreases. Figure 5 (d) shows that the standard curve of the fluorescence intensity of the detection system and the concentration of nitrite is linearly related, with a detection range of 0 - 250 μM and a detection limit of 1.06 μM.
Claims
1. A method for preparing lignin-based nitrogen-doped carbon dots with light-responsive simulated oxidase activity and green fluorescence, characterized in that: The sulfate lignin, m-phenylenediamine and concentrated nitric acid were dissolved in deionized water, stirred evenly and then subjected to hydrothermal reaction at 200°C for 24 hours to obtain lignin-based nitrogen-doped carbon dots with light-responsive simulated oxidase activity and green fluorescence, wherein the concentration of the sulfate lignin was 10 mg / mL, the mass ratio of the m-phenylenediamine to the sulfate lignin was 1:1, and the volume ratio of the concentrated nitric acid to deionized water was 5-20 μL:1 mL.
2. The preparation method according to claim 1, characterized in that: At room temperature, sulfate lignin, m-phenylenediamine and concentrated nitric acid are dissolved in deionized water, stirred and mixed evenly to obtain a brown-yellow solution; the dark brown solution obtained above is transferred to a high-pressure reactor, sealed and placed in a magnetic stirrer, stirred evenly and then subjected to hydrothermal reaction at 200°C for 24 hours, after the reaction is completed, cooled to room temperature to obtain a dark brown reaction liquid; the reaction liquid obtained above is subjected to ultrasonic, centrifugal and filtration treatments, and the clear liquid obtained by filtration is dialyzed with deionized water to obtain a solid product, which is dried to obtain lignin-based nitrogen-doped carbon dots with light-responsive simulated oxidase activity and green fluorescence.
3. The lignin-based nitrogen-doped carbon dots having light-responsive simulated oxidase activity and green fluorescence prepared by the method according to any one of claims 1 or 2, characterized in that: The lignin-based nitrogen-doped carbon dots are spherical nanoparticles with an average particle size of 1.25 to 1.75 nm; the optimal excitation wavelength of the lignin-based nitrogen-doped carbon dots is 445 nm, and the optimal emission wavelength is 515 nm.
4. The lignin-based nitrogen-doped carbon dots having light-responsive simulated oxidase activity and green fluorescence according to claim 3, characterized in that: The lignin-based nitrogen-doped carbon dots have photoluminescence and simulated oxidase activity, and when used, their catalytic ability can be stimulated by irradiation with visible light.
5. Use of the lignin-based nitrogen-doped carbon dots having light-responsive simulated oxidase activity and green fluorescence prepared by the method according to any one of claims 1 or 2, or the lignin-based nitrogen-doped carbon dots having light-responsive simulated oxidase activity and green fluorescence according to claim 3 or 4 in nitrite detection.
6. The use according to claim 5, characterized in that: The lignin-based nitrogen-doped carbon dots with light-responsive simulated oxidase activity and green fluorescence can simultaneously realize multi-mode detection of nitrite through colorimetry, ratiometry and fluorescence methods.
7. A colorimetric-ratiometric-fluorescence multimodal detection method for nitrite based on lignin-based nitrogen-doped carbon dots with light-responsive simulated oxidase activity and green fluorescence, characterized in that: The carbon dot aqueous solution was mixed with 3,3',5,5'-tetramethylbenzidine ethanol solution in acetic acid-sodium acetate buffer solution with a pH of 4 and then used at a light power density of 15 mW / m 2 The samples were irradiated with an EDL flashlight for 10 min, and then the sample solution containing nitrite was added and incubated for another 15 min. The color change of the solution was observed, and the absorbance and fluorescence intensity were measured to achieve colorimetric-ratio-fluorescence multi-mode detection of nitrite.
8. The detection method according to claim 7, characterized in that: The volume ratio of the carbon dot solution, 3,3',5,5'-tetramethylbenzidine ethanol solution, acetic acid-sodium acetate buffer solution and the test sample solution containing nitrite is 48:56:1862:35, wherein the concentration of the carbon dot aqueous solution is 1 mg / mL, and the concentration of the 3,3',5,5'-tetramethylbenzidine ethanol solution is 5 mM.
9. The use according to claim 7 or 8, characterized in that: The detection range of the colorimetric method is 0-250 μM, and the color gradually changes from blue to green and then to yellow as the nitrite concentration increases; the detection range of the ratio method is 0-250 μM, and the detection limit is 0.85 μM; the detection range of the fluorescence method is 0-250 μM, and the detection limit is 1.06 μM.