Preparation method and application of carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity

Abstract

The present invention relates to a preparation method and application of carboxymethyl cellulose-based manganese nitrogen-doped carbon dots with simulated oxidase activity, and belongs to the technical field of nanomaterial preparation and nitrite detection. The present invention dissolves sodium carboxymethyl cellulose, ethylenediamine and manganese chloride in deionized water, performs a hydrothermal reaction, and prepares carbon dots, wherein the concentration of sodium carboxymethyl cellulose is 0.04 g / mL, the mass ratio of ethylenediamine to sodium carboxymethyl cellulose is 0.5-1.5:1, and the mass ratio of manganese chloride to sodium carboxymethyl cellulose is 1:1. The present invention prepares manganese nitrogen carbon dots from cellulose-based precursors, and the raw materials and processes are green and environmentally friendly, low in cost, simple in equipment and process, and are conducive to large-scale production. The manganese nitrogen carbon dots prepared by the present invention have both fluorescence and simulated oxidase activity, can realize colorimetric-ratio-fluorescence "multi-mode" detection of nitrite, have the advantages of high sensitivity, high accuracy, strong anti-interference ability, etc., and are conducive to expanding the application field of carbon dots.

Description

Technical Field

[0001] The invention relates to a preparation method and application of carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity, belonging to the technical field of nanomaterial preparation and nitrite detection. Background Art

[0002] Nanozymes have the advantages of high stability, low cost and adjustable enzyme activity. They can be used as substitutes for natural enzymes and have attracted widespread attention from researchers. At present, nanozymes mainly include metal-organic frameworks, metal single atoms / diatoms, metal oxides and carbon materials. Among them, carbon dots are a low-dimensional carbon material with a size of less than 10 nm, which has the advantages of easy preparation, low toxicity, biocompatibility and good dispersibility. In the reports of carbon dot nanozymes, researchers usually use structural design or heteroatom doping methods to give or improve the catalytic ability of carbon dots. In addition to mimicking enzyme activity, carbon dots also have excellent intrinsic photoluminescence ability. Therefore, the combination of photoluminescence characteristics and mimicking enzyme activity has opened up new avenues for carbon dots in the biomedical field (antibacterial, anti-inflammatory and cancer treatment, etc.) and multimodal sensing fields.

[0003] Current research on carbon dots mimicking enzyme activity primarily focuses on peroxidase activity. Carbon dots (CDs) with peroxidase-mimicking properties require the introduction of unstable hydrogen peroxide during use, potentially leading to unexpected risks and errors. As another member of the nanozyme family, oxidase-mimicking CDs require only the presence of dissolved oxygen for catalysis, making their applications more flexible and broad. In related reports, researchers have used small-molecule carbon sources such as citric acid, serine, and ethylenediaminetetraacetic acid to prepare CDs with oxidase-mimicking activity. However, small-molecule carbon sources often suffer from non-renewable properties or high production and processing costs. The current demands for carbon neutrality and industrial production are spurring researchers to seek renewable, low-cost materials for CD production. Lignocellulosic biomass, comprising cellulose, lignin, and hemicellulose, is a green, renewable natural resource. Its renewable nature, abundance, and low cost make it an ideal carbon source for the industrial production of low-cost CDs. Lignin, a polymer composed of phenylpropane units, has relatively few reactive functional groups, and CDs prepared from it have very low quantum efficiencies. Although hemicellulose possesses a rich array of reactive functional groups, its heterogeneous structure makes the properties of CDs derived from it difficult to control and investigate. Cellulose, in contrast, possesses a more uniform structure and abundant reactive sites, facilitating the preparation of CDs. To date, most research on cellulose-based CDs has focused on photoluminescence, a relatively limited focus. Therefore, it is necessary to develop CDs that combine fluorescence properties with mimicking oxidase activity to expand their application.

[0004] Nitrite is a food additive commonly used to preserve meat products and inhibit the growth of microorganisms. However, nitrite binds to hemoglobin in the blood, interfering with oxygen transport, posing a particularly serious threat to pregnant women and infants. Furthermore, nitrite reacts with amino acids in the stomach to form the carcinogen N-nitrosamine. Currently, commonly used detection methods include ion chromatography, capillary electrophoresis, gas-phase chemiluminescence, and Griess reagent, but these methods often suffer from high costs and complex procedures. Fluorescence and colorimetric ratiometric methods can also be used to detect nitrite. In recent years, aromatic compounds containing primary amine groups, such as folic acid, neutral red, and anthocyanins, have been formulated into fluorescent materials for nitrite detection. Furthermore, materials with oxidase-mimicking activity, such as hollow MnFeO, CoMnO3 nanofibers, and Co-NC nanomaterials, have been used to detect nitrite using ratiometric colorimetry. However, these detection methods are single-shot and susceptible to environmental interference (for example, when the sample is colored or mixed with fluorescent substances), leading to inaccurate results. Therefore, there is an urgent need to develop a biomass-based CDs that can simultaneously possess photoluminescence properties and simulate oxidase activity, and use it to construct a colorimetric-ratio-fluorescence "multimodal" sensing system to improve the accuracy of nitrite detection. Summary of the Invention

[0005] In order to solve the technical problems existing in the existing carbon dot preparation process and the problem of inaccurate detection results caused by a single detection mode in the nitrite detection process, the present invention provides a method for preparing carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity and its application. The present invention uses naturally renewable, cheap and easily available sodium carboxymethyl cellulose (CMC) as a carbon source, ethylenediamine as a nitrogen dopant, and manganese chloride (MnCl2) as a manganese dopant. The carbon dots having both photoluminescence properties and simulated oxidase activity are prepared by a simple, green and environmentally friendly hydrothermal method, and are used for colorimetric-ratio-fluorescence "multi-mode" sensing detection of nitrite. The present invention has a simple process, is green and environmentally friendly, and has simple equipment. At the same time, the cost of the raw materials used is low, which is conducive to large-scale industrial production.

[0006] A method for preparing carboxymethyl cellulose-based manganese-nitrogen doped carbon dots with simulated oxidase activity comprises dissolving sodium carboxymethyl cellulose, ethylenediamine and manganese chloride in deionized water and performing a hydrothermal reaction to prepare the carbon dots.

[0007] In the method of the present invention, the concentration of the sodium carboxymethyl cellulose is 0.04 g / mL.

[0008] In the method of the present invention, the mass ratio of ethylenediamine to sodium carboxymethyl cellulose is 0.5-1.5:1.

[0009] Furthermore, when the mass ratio of ethylenediamine to sodium carboxymethyl cellulose increased from 0.5:1 to 1.5:1, the simulated oxidase activity of the carbon dots gradually increased; the fluorescence intensity increased significantly when the mass ratio of ethylenediamine to sodium carboxymethyl cellulose increased from 0.5:1 to 1:1, and decreased rapidly when it increased from 1:1 to 1.5:1.

[0010] Preferably, the mass ratio of ethylenediamine to sodium carboxymethyl cellulose is 1:1.

[0011] In the method of the present invention, the mass ratio of the manganese chloride to sodium carboxymethyl cellulose is 1:1.

[0012] In the method of the present invention, the temperature of the hydrothermal reaction is 220° C., and the reaction time is 12 to 36 hours.

[0013] Preferably, the hydrothermal reaction time is 36 hours.

[0014] The present invention preferably has a technical solution comprising the following steps:

[0015] S1: Dissolve sodium carboxymethyl cellulose, ethylenediamine, and manganese chloride in deionized water at room temperature and stir to mix thoroughly to obtain a transparent light yellow solution;

[0016] S2: Transfer the light yellow solution obtained in S1 to a high-pressure reactor, seal it, and place it in a magnetic stirrer for hydrothermal reaction. After the reaction is completed, cool it to room temperature to obtain a dark brown reaction solution;

[0017] S3: The reaction solution obtained in S2 is subjected to ultrasonic treatment, centrifugation, and filtration, and the filtered clear solution is dialyzed with deionized water to obtain a solid product;

[0018] S4: Drying the solid product obtained in S3 to obtain pure carbon dots.

[0019] In the method of the present invention, the ultrasonic conditions are as follows: ultrasonic dispersion for 20 minutes at a power of 100 W followed by ultrasonic dispersion for 2 seconds and rest for 3 seconds in an ultrasonic cell disruptor.

[0020] In the method of the present invention, the centrifugation condition is centrifugation at 5000 rpm for 5 minutes.

[0021] In the method of the present invention, the filtration method is to use a 0.22 μm water filter membrane to filter out insoluble precipitates in the solution to obtain a clear solution.

[0022] In the method of the present invention, the dialysis conditions are to purify the filtrate using a polycellulose ester dialysis bag with a molecular weight cutoff of 1000Da, the dialysis treatment time is 72h, and the water is changed every 8 to 12h.

[0023] In the method of the present invention, the drying condition is drying at 60° C. for 24 hours in a blast drying oven.

[0024] Another object of the present invention is to provide carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity prepared by the above method.

[0025] Furthermore, the carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity are spherical nanoparticles with an average particle size of 3.5 to 4.2 nm.

[0026] Another object of the present invention is to provide the use of the above-mentioned carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity in nitrite detection.

[0027] Furthermore, the carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity can achieve multimodal detection of nitrite through colorimetry, ratiometry and fluorescence methods.

[0028] A colorimetric-ratiometric-fluorescence multimodal detection method for nitrite based on carboxymethylcellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity. The carbon dot aqueous solution and 3,3',5,5'-tetramethylbenzidine ethanol solution are incubated in an acetic acid-sodium acetate buffer solution with a pH of 4 for 2 minutes. Then, a nitrite-containing solution is added and incubated for a further 15 minutes. The color change of the solution is observed, and the absorbance and fluorescence intensity are measured to achieve colorimetric-ratiometric-fluorescence multimodal detection of nitrite.

[0029] Furthermore, when the carbon dot aqueous solution is incubated with a 3,3',5,5'-tetramethylbenzidine ethanol solution in an acetic acid-sodium acetate buffer solution at pH 4 and then a nitrite-containing solution is added and the incubation is continued, the color, absorbance, and fluorescence intensity of the solution can change simultaneously, and nitrite can be detected simultaneously using colorimetry, ratiometry, and fluorescence methods.

[0030] In the above technical solution, the volume ratio of the carbon dot solution, 3,3',5,5'-tetramethylbenzidine ethanol solution, acetic acid-sodium acetate buffer solution and nitrite solution is 1:2:115:2.

[0031] Furthermore, 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.

[0032] Furthermore, the detection range of the colorimetric method is 0 to 300 μM, and the color gradually changes from blue to green and then to yellow as the concentration of nitrite increases.

[0033] Furthermore, the detection range of the ratiometric method is 0-200 μM, and the detection limit is 3.50 μM.

[0034] Furthermore, the detection range of the fluorescence method is 0-100 μM, and the detection limit is 1.06 μM.

[0035] The carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity of the present invention have the activity of simulating oxidase, which can reduce dissolved oxygen to superoxide anion radicals, and the superoxide anion radicals can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to TMB + , so that the solution turns blue and absorbs visible light at 652nm, and then the oxidized TMB + It can undergo a diazotization reaction with nitrite to change the solution from blue to green. As the concentration of nitrite increases, it gradually changes from green to yellow, realizing the visual detection of nitrite; TMB + The diazotization product generated with nitrite has an absorbance at 445nm, and the ratio of the absorbance at 652nm to that at 445nm (A652 / A445) is linearly related to the concentration of nitrite; TMB + The diazotization product generated by nitrite can quench the fluorescence of carbon dots, and the fluorescence intensity is linearly related to the concentration of nitrite.

[0036] Beneficial effects of the present invention:

[0037] (1) The present invention uses sodium carboxymethyl cellulose, a cellulose-modified product with abundant reserves in nature, renewable, green and pollution-free, and low cost, as a carbon source to prepare carbon dots, thus avoiding the problem of expensive and difficult to obtain carbon source materials. Furthermore, the present invention uses a simple and convenient one-step hydrothermal method to prepare carbon dots that have both simulated oxidase activity and fluorescent properties. The raw materials of the present invention are low-cost and widely available, and the preparation method is simple to operate, economical and environmentally friendly, which is conducive to the industrial large-scale production of carbon dots.

[0038] (2) The present invention uses biomass as a carbon source to prepare carbon dots with simulated oxidase activity, which opens up new avenues for the high-value application of cellulose and also provides a new, low-cost raw material for the development of carbon dot nanozymes.

[0039] (3) The carbon dots prepared by the present invention, which have both simulated oxidase activity and fluorescence properties, exhibit excellent TMB catalytic performance, with a maximum reaction rate (V max ) is 19.8×10 -5 mM s -1The Michaelis constant (Km) is 0.159 mM. The carbon dots prepared by the present invention can realize colorimetric, ratiometric, and fluorescence multimodal detection of nitrite with sensitive detection effects. The detection range of the colorimetric method is 0-300 μM; the detection range of the ratiometric method is 0-200 μM, with a detection limit of 3.50 μM; and the detection range of the fluorescence method is 0-100 μM, with a detection limit of 1.06 μM.

[0040] (4) The carbon dots prepared by the present invention have abundant functional groups such as carboxyl, hydroxyl, and amino groups on their surfaces, exhibiting good water solubility and dispersibility, and exhibit excellent biocompatibility. A sensing system based on these carbon dots (a solution system consisting of carbon dots, TMB, and a buffer solution) can be used to detect a variety of substances, including nitrite, glutathione, and dopamine. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 (a) Transmission electron microscopy image and (b) particle size distribution diagram of the carbon dots obtained in Example 1.

[0042] Figure 2 The fluorescence emission spectra of the carbon dots obtained in Example 5 at different excitation wavelengths (a) and in different pH environments (b).

[0043] Figure 3 This is the EPR spectrum of the carbon dots obtained in Example 5.

[0044] Figure 4 These are the detection results of nitrite by the carbon dots obtained in Example 5, wherein (a) is the UV-visible absorption spectrum of the carbon dots + TMB system in response to different concentrations of nitrite; (b) is the linear relationship between the A652 / A445 value and the nitrite concentration; (c) is the fluorescence spectrum of the carbon dots + TMB system in response to different concentrations of nitrite; (d) is the linear relationship between the F0 / F value and the nitrite concentration; (e) is the anti-interference ability test of the carbon dots + TMB system in detecting nitrite using the ratio method; and (f) is the anti-interference ability test of the carbon dots + TMB system in detecting nitrite using the fluorescence method.

[0045] Figure 5 This is a diagram showing the effect of visual detection of nitrite by carbon dots obtained in Example 5. DETAILED DESCRIPTION

[0046] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0047] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are all commercially available unless otherwise specified.

[0048] Example 1

[0049] A method for preparing carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity comprises the following steps:

[0050] 2g of sodium carboxymethyl cellulose, 2g of ethylenediamine (the mass ratio of ethylenediamine to sodium carboxymethyl cellulose is 1:1) and 2g of manganese chloride are added to a beaker containing 40mL of ultrapure water, stirred with a magnetic stirrer until uniformly mixed, and then transferred to a 100mL para-polyphenylene (PPL) liner; after the liner is sealed with a stainless steel reactor, it is heated using a magnetic stirrer equipped with a heating module. The hydrothermal reaction temperature is 220°C and the reaction time is 24h; after the reaction is completed, the reactor is cooled to room temperature and the obtained dark brown The reaction solution was ultrasonically dispersed for 20 minutes using an ultrasonic cell disruptor at 100W with a 2-second pause and a 3-second pause. The solution was then transferred to a 50-mL centrifuge tube and centrifuged at 5000 rpm for 10 minutes. The supernatant after centrifugation was collected and filtered using a 0.22-μm pinhole water filter membrane. The filtrate was then injected into a 1000-Da dialysis bag for purification. The purification time was 72 hours, and the water was changed every 8 to 12 hours. Finally, the dialyzed solution was dried in a forced air drying oven to obtain pure carbon dots.

[0051] The carbon dots were prepared in deionized water to a 1 mg / mL carbon dot aqueous solution. 25 μL of this solution and 50 μL of a 5 mM 3,3',5,5'-tetramethylbenzidine ethanol solution were added to 2875 μL of acetic acid-sodium acetate (pH 4) buffer and incubated for 2 minutes. The absorbance of the mixed solution at 652 nm was 0.28. The absorbance value reflects the strength of the carbon dot-mimicking oxidase activity.

[0052] Example 2

[0053] Referring to Example 1, the difference from Example 1 is that the mass ratio of ethylenediamine to sodium carboxymethylcellulose is 0.5:1. After the carbon dots prepared under this condition are incubated with TMB ethanol solution for 2 minutes, the absorbance at 652 nm is 0.03.

[0054] Example 3

[0055] Referring to Example 1, the difference from Example 1 is that the mass ratio of ethylenediamine to sodium carboxymethylcellulose is 1.5: 1. After the carbon dots prepared under this condition were incubated with TMB ethanol solution for 2 minutes, the absorbance at 652 nm was 0.38.

[0056] Example 4

[0057] Referring to Example 1, the difference from Example 1 is that the hydrothermal reaction time is 12 h. After the carbon dots prepared under this condition are incubated with TMB ethanol solution for 2 min, the absorbance at 652 nm is 0.2.

[0058] Example 5

[0059] Referring to Example 1, the difference from Example 1 is that the hydrothermal reaction time is 36 h. After the carbon dots prepared under this condition are incubated with TMB ethanol solution for 2 min, the absorbance at 652 nm is 0.62.

[0060] Result analysis:

[0061] Figure 1 The transmission electron micrograph and particle size distribution diagram of the carbon dots obtained in Example 1 show that the carbon dots are spherical nanoparticles with an average particle size of about 4 nm.

[0062] Figure 2 The fluorescence emission spectra of the carbon dots obtained in Example 5 at different concentrations (a) and excitation wavelengths (b) are shown. Figure 2 As can be seen from (a), the fluorescence intensity increases with the increase of carbon dot concentration. When the concentration is 0.12 mg / mL, the fluorescence intensity reaches the maximum. When the concentration exceeds 0.12 mg / mL, the fluorescence intensity gradually decreases due to the aggregation quenching effect. Figure 2 As can be seen in (b), the fluorescence of the carbon dots has an excitation-dependent behavior. As the excitation wavelength changes, the fluorescence emission wavelength also changes accordingly.

[0063] Figure 3 This is the EPR spectrum of the carbon dots obtained in Example 5. During the test, DMPO was used as a scavenger for superoxide anion radicals. Without the carbon dots, DMPO did not capture the radicals. However, with the carbon dots introduced, typical signals corresponding to superoxide anion radicals appeared, demonstrating that the carbon dots catalyze the color change of TMB by converting dissolved oxygen into superoxide anion radicals, which then rob TMB of its electrons, causing it to oxidize and turn blue.

[0064] Table 1 shows the raw materials, application conditions, maximum catalytic rate (V) of the carbon dots obtained in Example 5 and other carbon dots with simulated oxidase activity. max ) and substrate affinity (K m ) and other aspects. Carbon dots with simulated oxidase activity can be divided into two types, among which type 1 is metal-doped carbon dots and type 2 is non-metal-doped carbon dots. The latter requires ultraviolet or visible light activation to enable the carbon dots to produce oxidase-like activity. V of the carbon dots obtained in Example 5 of the present invention max It is much higher than the carbon dots of type II and does not require photoexcitation when used; the V maxCompared with the carbon dots of type 1, it still has an advantage. m The K value is lower than that of all reported carbon dots. m The carbon dots obtained in Example 5 have an excellent affinity for TMB. In addition, the carbon dots obtained in Example 5 use renewable biomass as a carbon source, which is more economical and sustainable than other carbon dots with mimic oxidase activity.

[0065] Table 1 Comparison of raw materials, application conditions, maximum catalytic rate (Vmax) and substrate affinity (K) between Example 5 and other carbon dots with simulated oxidase activity in the prior art m ) and other aspects of the comparison

[0066] in,

[0067] Literature [1]: Y.Zhang, M.Zhang, Y.Ma,

[0068] Literature [2]: X.Li, S.Ding, Z.Lyu, P.Tieu, M.Wang, Z.Feng, X.Pan, Y.Zhou,

[0069] Reference [3]: L. Wang, Y. Chen, Y. Ji, S. Zheng, F. Wang, C. Li, Cheap and portable paper chip with terrific oxidase-like activity and SERS enhancement performance for SERS-colorimetric bimodal detection of intracellular glutathione, Biosens. Bioelectron. 244 (2024) 115817.

[0070] Reference [4]: G. Wu, H. Qiu, C. Du, Z. Zheng, Q. Liu, Z. Wang, P. Luo, Y. Shen, Intelligent onsite dual-modal assay based on oxidase-like fluorescence carbon dots-driven competitive effect for ethyl carbamate detection, J. Hazard. Mater. 474 (2024) 134707.

[0071] Reference [5]: J. Li, Y. Zhou, Y. Xiao, S. Cai, C. Huang, S. Guo, Y. Sun, R. Bin Song, Z. Li, Carbon dots as light-responsive oxidase-like nanozyme for colorimetric detection of total antioxidant capacity in fruits, Food Chem. 405 (2023) 134749.

[0072] Reference [6]: Z. Jia, Y. Liu, L. Cheng, Z. Deng, M. Zhang, H. Tuo, Carbon dots with light-responsive oxidase-like activity for colorimetric detection of dopamine and the catalytic mechanism, Front. Chem. 11 (2023) 1–11.

[0073] Literature[7]:

[0074] Figure 4 This is the effect diagram of the carbon dots obtained in Example 5 on nitrite detection using the sensing system constructed with the assistance of TMB. The construction method is as follows: carbon dots are prepared with deionized water to form a carbon dot aqueous solution with a concentration of 1 mg / mL, 25 μL of carbon dot solution and 50 μL of 3,3',5,5'-tetramethylbenzidine ethanol solution (concentration of 5 mM) are added to 2875 μL of acetic acid-sodium acetate (pH=4) buffer solution and incubated for 2 minutes, 50 μL of sodium nitrite solution of different concentrations are added and incubated for 15 minutes, the color change is observed, and then the obtained solution is respectively detected by fluorescence spectrophotometer for fluorescence intensity and UV-visible spectrophotometer for absorbance. Figure 4 As can be seen in (a), when the nitrite concentration increases, the absorbance of the carbon dots + TMB system at 445 nm increases rapidly, and the absorbance at 652 nm decreases slightly. Figure 4 (b) shows that the absorbance ratio at 652 nm and 445 nm is linearly related to the concentration of nitrite, and the calculated detection limit is 3.50 μM. Figure 4 As can be seen in (c), as the nitrite concentration increases, the fluorescence intensity of the carbon dots + TMB system gradually decreases. Figure 4 (d) shows that the fluorescence intensity of the detection system is linearly related to the concentration of nitrite, and the calculated detection limit is 1.06μM. In addition, Figure 4 (e) and Figure 4 (f) The carbon dots + TMB detection system has excellent anti-interference ability for both the ratiometric method and the fluorescence method of nitrite ions.

[0075] Figure 5 The carbon dots obtained in Example 5 were incubated with TMB ethanol solution for 2 minutes, and the color of the solution after the introduction of different concentrations of nitrite was changed to achieve visual detection of nitrite. Figure 5 It can be seen that as the concentration of nitrite increases, the color of the detection system gradually changes from blue to green and finally to yellow, and the detection range is 0-300 μM.

Claims

1. A method for preparing carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity, characterized by: Sodium carboxymethyl cellulose, ethylenediamine and manganese chloride are dissolved in deionized water and subjected to hydrothermal reaction to prepare carbon dots, wherein: The concentration of the sodium carboxymethyl cellulose is 0.04 g / mL, the mass ratio of ethylenediamine to sodium carboxymethyl cellulose is 0.5-1.5:1, and the mass ratio of manganese chloride to sodium carboxymethyl cellulose is 1:

1.

2. The preparation method according to claim 1, wherein: The temperature of the hydrothermal reaction is 220° C., and the reaction time is 12 to 36 hours.

3. The preparation method according to claim 1, wherein: The steps include: S1: Dissolve sodium carboxymethyl cellulose, ethylenediamine, and manganese chloride in deionized water at room temperature and stir to mix thoroughly to obtain a transparent light yellow solution; S2: Transfer the light yellow solution obtained in S1 to a high-pressure reactor, seal it, and place it in a magnetic stirrer for hydrothermal reaction. After the reaction is completed, cool it to room temperature to obtain a dark brown reaction solution; S3: The reaction solution obtained in S2 is subjected to ultrasonic treatment, centrifugation, and filtration, and the filtered clear solution is dialyzed with deionized water to obtain a solid product; S4: Drying the solid product obtained in S3 to obtain pure carbon dots.

4. Carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity prepared by the method according to any one of claims 1 to 3.

5. The carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity according to claim 4, characterized in that: The carbon dots are spherical nanoparticles with an average particle size of 3.5-4.2 nm.

6. Use of the carboxymethyl cellulose-based manganese-nitrogen doped carbon dots with simulated oxidase activity according to claim 4 in nitrite detection.

7. The use according to claim 6, characterized in that: The carboxymethyl cellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity can simultaneously realize multi-mode detection of nitrite through colorimetry, ratiometry and fluorescence.

8. A colorimetric-ratiometric-fluorimetric multimodal detection method for nitrite based on carboxymethylcellulose-based manganese-nitrogen-doped carbon dots with simulated oxidase activity, characterized by: An aqueous solution of carbon dots and an ethanol solution of 3, 3', 5, 5'-tetramethylbenzidine are incubated in an acetic acid-sodium acetate buffer solution at pH 4 for 2 min, and then a solution containing nitrite is added and incubated for a further 15 min. The color change of the solution is observed, and the absorbance and fluorescence intensity are measured to achieve colorimetric-ratiometric-fluorescence multimodal detection of nitrite, wherein the carbon dots are the carbon dots described in claim 4.

9. The detection method according to claim 8, wherein: The volume ratio of the carbon dot solution, 3, 3', 5, 5'-tetramethylbenzidine solution, acetic acid-sodium acetate buffer solution, and nitrite-containing solution is 1:2:115:2, 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.

10. The method according to claim 8 or 9, characterized in that: The detection range of the colorimetric method is 0-300 μM, and the color gradually changes from blue to green and then to yellow as the nitrite concentration increases; the detection range of the ratiometric method is 0-200 μM, and the detection limit is 3.50 μM; the detection range of the fluorescence method is 0-100 μM, and the detection limit is 1.06 μM.

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