Preparation method and application of cerium-doped graphite phase carbon nitride nanozyme

Abstract

The present invention provides a preparation method and application of cerium-doped graphitic carbon nitride nanozyme. The specific preparation method includes Step 1: Dissolve cerium nitrate hexahydrate in deionized water, add an appropriate amount of hydrogen peroxide to promote the oxidation of Ce<supgt;3+< / supgt;, and stir for 5 - 10 min to form a yellow solution; Step 2: Add urea to the solution obtained in Step 1, continue to stir for 0.5 - 4 h, and dry the obtained solution in an oven at 60 - 80 °C for 4 - 10 h; Step 3: Grind the dried sample, and then place it in a muffle furnace and calcine it at a constant temperature of 550 °C for 2 - 4 h; Step 4: After cooling to room temperature, thoroughly grind the obtained product in an agate mortar to obtain powdery cerium-doped graphitic carbon nitride nanozyme. The present invention also provides a method for applying the obtained cerium-doped graphitic carbon nitride nanozyme to the detection of tetracycline. The preparation method of the present invention is simple, convenient, and easy to control, and can realize the large-scale production of nanozymes.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials and analytical detection, and specifically relates to a preparation method of a cerium-doped graphite phase carbon nitride nanozyme and an application thereof in tetracycline detection. Background Art

[0002] Enzymes are highly efficient biocatalysts that play an important role in many fields, including metabolism in organisms, disease diagnosis and treatment, degradation of environmental pollutants, and analytical detection. However, natural enzymes have disadvantages such as easy inactivation, complex preparation process, and high cost, which limit their application. Nanozymes are a new type of catalytic nanomaterials that exhibit catalytic mechanisms and enzymatic reaction kinetics similar to those of natural enzymes. They have the advantages of low synthesis cost, stable and easy storage, adjustable catalytic activity, sensitive response to external stimuli, and easy modification. They are excellent substitutes for natural enzymes. Therefore, it is particularly important to develop simple, efficient, and low-cost methods for preparing nanozymes.

[0003] In terms of antibiotic detection, nanozymes have opened up new avenues for the development of new and highly sensitive detection methods. The traditional colorimetric method for detecting antibiotics based on nanozymes is low-cost and simple to operate, but its lack of sensitivity is also becoming increasingly prominent. Especially when faced with extremely low concentrations of antibiotic residues, the color changes of the colorimetric method are often not obvious enough, making it difficult to meet the needs of high-precision detection. In order to improve the sensitivity of antibiotic detection, researchers have begun to explore new detection methods, among which fluorescence analysis has attracted much attention due to its high sensitivity. Fluorescence analysis quantitatively analyzes substances by measuring the fluorescence intensity of the substance. Its sensitivity is hundreds to thousands of times higher than that of the colorimetric method, thus showing obvious superiority in highly sensitive detection tasks.

[0004] Based on the above background, the present invention proposes a method for preparing cerium-doped graphite carbon nitride nanozyme, aiming to achieve large-scale production of nanozymes in a simple, convenient and easy-to-control manner. In addition, the present invention also utilizes the fluorescence characteristics of 3,3',5,5'-tetramethylbenzidine (TMB), and affects the fluorescence intensity of TMB through the competitive interaction between tetracycline, TMB and cerium-doped graphite carbon nitride, and applies cerium-doped graphite carbon nitride nanozyme in the fluorescence detection of tetracycline. This detection method is not only simple to operate, short in time and low in cost, but also has high sensitivity and good selectivity, providing a new solution for the field of antibiotic detection. Summary of the invention

[0005] In view of the problems existing in the prior art, the technical solutions adopted by the present invention to solve the problems existing in the prior art are as follows:

[0006] A method for preparing cerium-doped graphite phase carbon nitride nanozyme comprises the following steps:

[0007] Step 1: Dissolve cerium nitrate hexahydrate in deionized water and add an appropriate amount of hydrogen peroxide to promote Ce 3+ Oxidation, stirring for 5-10 min, forming a yellow solution;

[0008] Step 2: Add urea to the above solution, continue stirring for 0.5-4 h, and dry the resulting solution in an oven at 60-80 °C for 4-10 h;

[0009] Step 3: Grind the dried sample, place it in a muffle furnace, heat it to 550 °C, and calcine it at a constant temperature for 2-4 h;

[0010] Step 4: After cooling to room temperature, the obtained product is fully ground in an agate mortar to obtain a powdered nanomaterial, namely, cerium-doped graphite phase carbon nitride nanozyme.

[0011] The amount of cerium nitrate hexahydrate added in step 1 is 0.413-0.964 g, and 120-200 μL of 30% hydrogen peroxide is added to promote the Ce 3+ Oxidation, the amount of urea added in step 2 is 4 g.

[0012] The heating rate of the muffle furnace in step 3 is 1-5 ℃･min -1 .

[0013] The present invention also includes an application of the cerium-doped graphite phase carbon nitride nanozyme obtained based on the above-mentioned preparation method, that is, a method for fluorescent detection of tetracycline based on the cerium-doped graphite phase carbon nitride nanozyme, comprising the following steps:

[0014] Step S1: Prepare a blank sample without tetracycline: add 0.04-0.08 mg / mL cerium-doped graphite phase carbon nitride nanozyme and 4-10 µmol / L TMB into acetic acid-sodium acetate (pH=3.0-5.0) buffer;

[0015] Step S2: reacting the solution obtained in step S1 at room temperature for 10-30 minutes;

[0016] Step S3: Record the fluorescence spectrum of the solution obtained in step S2 using a fluorescence spectrometer, and the fluorescence intensity of the system at 400 nm is recorded as F0;

[0017] Step S4: preparing samples containing different concentrations of tetracycline: adding 0.5-7.0 µg / mL tetracycline, 0.04-0.08 mg / mL cerium-doped graphite carbon nitride nanozyme and 4-10 µmol / L TMB into acetic acid-sodium acetate (pH=3.0-5.0) buffer;

[0018] Step S5: reacting the several groups of solutions obtained in step S4 at room temperature for 10-30 minutes;

[0019] Step S6: using a fluorescence spectrometer to record the fluorescence intensity of each reaction system of the several groups of solutions obtained in step S5, and the fluorescence intensity of the system at 400 nm is recorded as F;

[0020] Step S7: The fluorescence intensity F of the sample containing tetracycline minus the fluorescence intensity F0 of the sample not containing tetracycline is recorded as DF. After adding tetracycline, the fluorescence change rate of the system is calculated as DF / F0;

[0021] Step S8: Establish a standard curve between the fluorescence change rate of the system and the tetracycline concentration, with the fluorescence change rate of the system after adding tetracycline as the ordinate and the tetracycline concentration as the abscissa; and detect the content of tetracycline in the sample based on the established standard curve.

[0022] In step S1, the concentration of the acetic acid-sodium acetate buffer solution is 0.10 mol / L, and the pH of the acetic acid-sodium acetate buffer solution is 4.0; the concentration of the cerium-doped carbon nitride nanozyme is 0.05 mg / mL; and the concentration of TMB is 5 µmol / L;

[0023] The instrument parameters of the fluorescence spectrometer in step S3 and step S6 are: excitation wavelength 281 nm, emission wavelength 350-450 nm, excitation voltage 700 V, and slit width 5 nm.

[0024] Furthermore, the tetracycline in step S4 can be replaced with penicillin G sodium, cephalosporin, ampicillin, amoxicillin, and chloramphenicol at a concentration of 4.0 µg / mL, and the test can be performed according to the experimental method of steps S4-S7 to evaluate the effect of other antibiotics on the fluorescence intensity of the system and investigate the selectivity of the established fluorescence detection method for tetracycline;

[0025] For a specific experimental sample, the tetracycline content therein is detected and calculated using steps S1-S8. After adding tetracycline of different concentrations to the experimental sample, the experiment is continued according to the experimental method of steps S4-S7, the fluorescence change rate DF / F0 is calculated, and the DF / F0 value is substituted into the standard curve equation in step S8 to calculate the detection concentration of tetracycline. The ratio of the tetracycline detection concentration and the corresponding spiked concentration is the spiked recovery rate. The practicability of the detection method is verified by the spiked recovery rate.

[0026] The present invention has the following advantages:

[0027] The present invention proposes a method for preparing a cerium-doped graphite carbon nitride nanozyme. Cerium, as a rare earth element, has unique chemical properties and electronic structure. The present invention dopes cerium into graphite carbon nitride to significantly change its energy band structure and electron distribution. The prepared nanozyme has a multilayer sheet structure, a high specific surface area and catalytic performance. At the same time, by precisely controlling the reaction conditions and parameters (such as stirring time, drying temperature, calcination temperature and time, etc.), a cerium-doped graphite carbon nitride nanozyme with good stability and repeatability can be prepared. The entire synthesis process is simple and convenient, so that the method has great application potential in industrial production.

[0028] The present invention uses TMB as a fluorescent indicator, utilizes the competitive interaction between tetracycline, TMB and cerium-doped graphite phase carbon nitride nanozyme to affect the fluorescence intensity of TMB, and establishes a fluorescence detection method based on cerium-doped graphite phase carbon nitride nanozyme for the detection of tetracycline. The method has a simple operation process, and only requires adding a certain amount of each substance to an acetic acid-sodium acetate buffer for a one-step reaction. The entire detection process can be completed within 1 hour, with short time consumption, low cost and high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an X-ray diffraction pattern of the cerium-doped graphite phase carbon nitride prepared in Example 1 of the present invention;

[0030] Figure 2 This is a scanning electron microscope image of the cerium-doped graphite phase carbon nitride prepared in Example 1 of the present invention;

[0031] Figure 3 This is a Fourier transform infrared spectrum of the cerium-doped graphite phase carbon nitride prepared in Example 1 of the present invention;

[0032] Figure 4 This is a graph showing the oxidase activity of the cerium-doped graphite-phase carbon nitride prepared in Example 1 of the present invention;

[0033] Figure 5 The fluorescence spectra of tetracycline at different concentrations added to the cerium-doped graphite carbon nitride-TMB system (A) and the linear relationship between the fluorescence intensity change rate at 400 nm and the tetracycline concentration (B);

[0034] Figure 6 The cerium-doped graphite phase carbon nitride nanozyme prepared in Example 1 of the present invention is applied to the selectivity of fluorescent detection of tetracycline. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further specifically described below through examples and in conjunction with the accompanying drawings. Example 1: A method for preparing a cerium-doped graphite phase carbon nitride nanozyme, comprising the following steps:

[0036] Step 1: Dissolve 0.578 g of cerium nitrate in 5 mL of deionized water, add 120 µL of 30% H2O2 solution, and stir for 5 min to form a yellow solution;

[0037] Step 2: Add 4 g of urea to the above solution, continue stirring for 2.5 h, and then dry the resulting solution in an oven at 80 °C for 8 h;

[0038] Step 3: Grind the dried sample and place it in a muffle furnace at 3 °C･min -1 The temperature was raised to 550 °C at a heating rate of 1.5 °C and calcined at a constant temperature for 3 h;

[0039] Step 4: Cool the sample obtained after calcination in step 3 to room temperature, and grind the obtained product in an agate mortar to obtain a powdered nanomaterial, i.e., cerium-doped graphite phase carbon nitride nanozyme;

[0040] Step 5: Perform X-ray diffraction and scanning electron microscopy characterization tests on the prepared samples to obtain Figure 1 and Figure 2 relevant data;

[0041] Step 6: Perform Fourier transform infrared spectroscopy test on the prepared samples to obtain Figure 3 relevant data;

[0042] Step 7: Add 0.67 mmol / L TMB to the first set of acetic acid-sodium acetate (pH = 4.0) buffer solution;

[0043] 0.03 mg / mL graphite carbon nitride nanozyme and 0.67 mmol / L TMB were added to the second group of acetic acid-sodium acetate (pH=4.0) buffer solution; 0.03 mg / mL graphite carbon nitride nanozyme was added to the third group of acetic acid-sodium acetate (pH=4.0) buffer solution;

[0044] Step 8: The three groups of solutions obtained in step 7 were allowed to stand at room temperature for 20 minutes, the color change of the system was observed and the UV-visible absorption spectrum of the samples was collected to obtain Figure 4 Related data.

[0045] Figure 1The X-ray diffraction patterns of graphite carbon nitride and cerium-doped graphite carbon nitride. The diffraction peaks at 13.11° and 27.74° are attributed to the (100) and (002) crystal planes of graphite carbon nitride, respectively. Compared with graphite carbon nitride, the characteristic diffraction peak of cerium-doped graphite carbon nitride shifts to the right at a small angle, indicating that cerium is doped into graphite carbon nitride. At the same time, cerium-doped graphite carbon nitride has an obvious diffraction peak at 43.92°, which corresponds to the standard card JCPDS no.49-1415, that is, CeO 2-x (044) crystal plane. This is due to the Ce ions that appeared when cerium nitrate was oxidized by hydrogen peroxide during the sample synthesis stage. 3+ and Ce 4 + The coexistence of the mixture and a small amount of CeO on the surface of graphite carbon nitride 2-x .

[0046] Figure 2 The morphology is that of cerium-doped graphite-phase carbon nitride. The nanomaterial presents a multilayered sheet structure with some holes.

[0047] Figure 3 Infrared spectrum of Ce-doped graphene-phase carbon nitride nanozyme, at 3400-3000 cm -1 The broad absorption peaks appearing near are attributed to the symmetric and asymmetric stretching vibrations of the amino group. The characteristic absorption peak at 2170 cm⁻¹ corresponds to the typical stretching vibration of the C≡N bond, and the peaks at 1680-1200 cm -1 A series of absorption peaks appearing in the range are related to the stretching vibration of the aromatic ring in carbon nitride, and the characteristic peak at 809 cm⁻¹ is closely related to the bending vibration of the triazine ring. The above results indicate that the obtained product is a multilayer flaky cerium-doped graphite phase carbon nitride nanomaterial.

[0048] Figure 4 The figure shows the oxidase activity assay of cerium-doped graphite carbon nitride. The solutions of TMB and cerium-doped carbon nitride are colorless, and the UV-visible absorption spectrum is close to a straight line, while the mixed solution of TMB and cerium-doped graphite carbon nitride nanomaterials is blue, and there is an absorption peak in the range of 500-750 nm, with a maximum absorption wavelength of around 652 nm, indicating that cerium-doped graphite carbon nitride nanomaterials have oxidase properties.

[0049] Example 2: A fluorescence detection method for detecting tetracycline based on cerium-doped graphite phase carbon nitride nanozyme, comprising the following steps:

[0050] Step S1: Prepare a blank sample without tetracycline: add 0.05 mg / mL cerium-doped graphite phase carbon nitride nanozyme and 5 µmol / L TMB into acetic acid-sodium acetate (pH=4.0) buffer;

[0051] Step S2: leaving the reaction solution to stand at room temperature for 20 minutes;

[0052] Step S3: Record the fluorescence spectrum of the reaction system using a fluorescence spectrometer. The instrument parameters are: excitation wavelength 281 nm, emission wavelength 350-450 nm, excitation voltage 700 V, slit 5 nm. The fluorescence intensity of the system at 400 nm is recorded as F0.

[0053] Step S4: preparing samples containing different concentrations of tetracycline: adding tetracycline at concentrations of 0.5, 1, 2, 3, 4, 5, 6, and 7 µg / mL, 0.05 mg / mL cerium-doped graphite carbon nitride nanozyme, and 5 µmol / L TMB into acetic acid-sodium acetate (pH=4.0) buffer;

[0054] Step S5: leaving the reaction solution to stand at room temperature for 20 minutes;

[0055] Step S6: Record the fluorescence intensity of each reaction system using a fluorescence spectrometer. The instrument parameters are: excitation wavelength 281 nm, emission wavelength 350-450 nm, excitation voltage 700 V, slit 5 nm, and the fluorescence intensity of the system at 400 nm is recorded as F.

[0056] Step S7: The fluorescence intensity F of the sample containing tetracycline minus the fluorescence intensity F0 of the sample not containing tetracycline is recorded as DF. After adding tetracycline, the fluorescence change rate of the system is calculated as DF / F0;

[0057] Step S8: With the fluorescence change rate of the system after adding tetracycline as the ordinate and the tetracycline concentration as the abscissa, a standard curve between the fluorescence change rate of the system and the tetracycline concentration is established to obtain Figure 5 relevant data;

[0058] like Figure 5 As shown in the figure, with the increase of tetracycline concentration, the fluorescence of the system at 400 nm gradually increased. In the concentration range of 0.5 to 7 µg / mL, there was a good linear relationship between the fluorescence change rate DF / F0 and the tetracycline concentration. The linear expression was y = 0.5497x + 0.0518, and the correlation coefficient R 2 =0.9972. According to LOD=3σ / k, the detection limit (LOD) is calculated to be 55.7 ng / mL. Where σ is the standard deviation of the sample and k is the slope of the standard curve.

[0059] Example 3: Selectivity of cerium-doped graphite phase carbon nitride nanozyme for fluorescence detection of tetracycline:

[0060] In order to evaluate the selectivity of the above analytical method, several other antibiotics, including penicillin G sodium, cephalosporin, ampicillin, amoxicillin and chloramphenicol, were used for control experiments to evaluate their effects on the fluorescence intensity of the system.

[0061] Step 1): Prepare a blank sample: add 0.05 mg / mL cerium-doped graphite phase carbon nitride nanozyme and 5 µmol / L TMB into acetic acid-sodium acetate (pH=4.0) buffer;

[0062] Step 2): The reaction solution was allowed to stand at room temperature for 20 minutes;

[0063] Step 3): Use a fluorescence spectrometer to record the fluorescence spectrum of the reaction system. The instrument parameters are: excitation wavelength 281 nm, emission wavelength 350-450 nm, excitation voltage 700 V, slit 5 nm, and the fluorescence intensity of the system at 400 nm is recorded as F0.

[0064] Step 4): Prepare a sample containing tetracycline. Add 4.0 µg / mL tetracycline, 0.05 mg / mL cerium-doped graphite carbon nitride nanozyme and 5 µmol / L TMB into acetic acid-sodium acetate (pH=4.0) buffer;

[0065] Step 5): Prepare samples containing penicillin G sodium, cephalosporin, ampicillin, amoxicillin and chloramphenicol respectively, and replace the tetracycline in step 4) with penicillin G sodium, cephalosporin, ampicillin, amoxicillin and chloramphenicol at the same concentration;

[0066] Step 6): Let the solution of step 4)-5) stand at room temperature for 20 minutes;

[0067] Step 7): Use a fluorescence spectrometer to record the fluorescence intensity of each reaction system after standing in step 6). The instrument parameters are: excitation wavelength 281 nm, emission wavelength 350-450 nm, excitation voltage 700 V, slit 5 nm, and the fluorescence intensity of the system at 400 nm is recorded as F.

[0068] Step 8): The fluorescence intensity F of the sample in step 7) minus the fluorescence intensity F0 of the sample in step 3) is recorded as DF, and the fluorescence change rate of the system is calculated as DF / F0;

[0069] Step 9): Compare the change rate DF / F0 of the fluorescence intensity of the system caused by tetracycline, penicillin G sodium, cephalosporin, ampicillin, amoxicillin and chloramphenicol.

[0070] The results are as follows Figure 6As shown in the figure, under the same test conditions, tetracycline caused the largest fluorescence change rate, while other antibiotics caused smaller fluorescence change rates. This result shows that the proposed method for detecting tetracycline based on cerium-doped graphene phase carbon nitride nanozymes has significant selectivity and excellent anti-interference ability.

[0071] Example 4, detection of tetracycline in milk samples:

[0072] The detection method proposed in the present invention was applied to the detection of tetracycline in actual samples (milk), and a spike recovery experiment was carried out for verification.

[0073] Fluorescence measurement of blank samples: 0.05 mg / mL cerium-doped graphite carbon nitride nanozyme and 5 µmol / L TMB were added to acetic acid-sodium acetate (pH=4.0) buffer; the above solution was allowed to stand at room temperature for 20 minutes; the fluorescence spectrum of the reaction system was recorded using a fluorescence spectrometer, and the fluorescence intensity of the system at 400 nm was recorded as F0.

[0074] Fluorescence measurement of milk samples:

[0075] 300 µL of milk sample was added to 300 µL of ethyl acetate; 15 µL of tetracycline solution of different concentrations was added to 300 µL of milk sample, and then 300 µL of ethyl acetate was added; each sample solution was ultrasonicated for 12 min, centrifuged at 10000 r / min for 10 min, and the supernatant was transferred to another centrifuge tube; the supernatant was dried under nitrogen and then dissolved in 15 µL of deionized water; acetic acid-sodium acetate (pH=4.0) buffer, 0.05 mg / mL cerium-doped graphite phase carbon nitride nanozyme and 5 µmol / L TMB were added, and the total volume of the solution was 300 µL; the above solution was allowed to stand at room temperature for 20 minutes; the fluorescence spectrum of the reaction system was recorded using a fluorescence spectrometer, and the fluorescence intensity of the system at 400 nm was recorded as F.

[0076] The fluorescence intensity F of the milk sample minus the fluorescence intensity F0 of the blank sample is recorded as DF, and the fluorescence change rate of the system is calculated by DF / F0; the fluorescence change rate DF / F0 of the milk sample is substituted into the linear equation y = 0.5497x + 0.0518 to obtain the tetracycline concentration in the milk sample, and the recovery rate is calculated by measuring the ratio of the tetracycline concentration and the spiked tetracycline concentration.

[0077] The results are shown in Table 1. The spiked recovery rate of tetracycline detected by this method is 96.8%-106.8%, indicating that the detection method proposed in the present invention can be used for sensitive detection of tetracycline in actual samples (milk) and has good practicality.

[0078] Table 1 Recovery of tetracycline in milk

[0079]

[0080] In the above embodiment, the synthesis process of cerium-doped graphite phase carbon nitride nanozyme is simple and efficient, and common raw materials and instruments are used. The established fluorescence detection method can easily detect tetracycline by simply mixing the samples, successfully avoiding the high cost and various uncontrollable factors caused by complex detection conditions. The method can complete the detection of tetracycline within 1 hour, has a short detection cycle, is simple to operate, has high sensitivity and good selectivity, and also obtains an ideal recovery rate for the detection of tetracycline in actual samples, which provides a new idea for the detection of tetracycline in food and has broad application prospects.

[0081] The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims

1. An application of cerium-doped graphite phase carbon nitride nanozyme, characterized in that: The preparation method of the cerium-doped graphite phase carbon nitride nanozyme comprises the following steps: Step 1: Dissolve cerium nitrate hexahydrate in deionized water and add an appropriate amount of hydrogen peroxide to promote Ce 3+ Oxidation, stirring for 5-10 min, forming a yellow solution; Step 2: Add urea to the solution obtained in step 1, continue stirring for 0.5-4 h, and dry the resulting solution in an oven at 60-80 °C for 4-10 h; Step 3: Grind the dried sample, place it in a muffle furnace, heat it to 550 °C, and calcine it at a constant temperature for 2-4 hours; Step 4: After cooling to room temperature, the obtained product is fully ground in an agate mortar to obtain a powdered nanomaterial, namely, cerium-doped graphite phase carbon nitride nanozyme; The amount of cerium nitrate hexahydrate added in step 1 is 0.413-0.964 g, and 120-200 μL of 30% hydrogen peroxide is added to promote the Ce 3+ Oxidation; The application includes a method for fluorescent detection of tetracycline based on cerium-doped graphite phase carbon nitride nanozyme, which specifically includes the following steps: Step S1: prepare a blank sample without tetracycline: add 0.04-0.08 mg / mL cerium-doped graphite phase carbon nitride nanozyme and 4-10 µmol / L TMB into acetic acid-sodium acetate buffer at pH=3.0-5.0; Step S2: reacting the solution obtained in step S1 at room temperature for 10-30 minutes; Step S3: Record the fluorescence spectrum of the solution obtained in step S2 using a fluorescence spectrometer, and the fluorescence intensity of the system at 400 nm is recorded as F0; Step S4: preparing several groups of samples containing different concentrations of tetracycline: adding 0.5-7.0 µg / mL tetracycline, 0.04-0.08 mg / mL cerium-doped graphite carbon nitride nanozyme and 4-10 µmol / L TMB to an acetic acid-sodium acetate buffer at pH=3.0-5.0; Step S5: reacting the several groups of solutions obtained in step S4 at room temperature for 10-30 minutes to obtain several groups of reaction systems; Step S6: using a fluorescence spectrometer to record the fluorescence intensity of the reaction systems obtained in step S5, where the fluorescence intensity of the system at 400 nm is recorded as F; Step S7: The fluorescence intensity F of the sample containing tetracycline minus the fluorescence intensity F0 of the sample not containing tetracycline is recorded as DF. After adding tetracycline, the fluorescence change rate of the system is calculated as DF / F0; Step S8: Establish a standard curve between the fluorescence change rate of the system and the tetracycline concentration, with the fluorescence change rate of the system after adding tetracycline as the ordinate and the tetracycline concentration as the abscissa; and detect the content of tetracycline in the sample based on the established standard curve.

2. The use of a cerium-doped graphite phase carbon nitride nanozyme as claimed in claim 1, characterized in that: The amount of urea added in step 2 is 4 g.

3. The use of a cerium-doped graphite phase carbon nitride nanozyme as claimed in claim 1, characterized in that: The heating rate of the muffle furnace in step 3 is 1-5 ℃･min -1 .

4. The use of a cerium-doped graphite phase carbon nitride nanozyme as claimed in claim 1, characterized in that: In step S1, the concentration of the acetic acid-sodium acetate buffer solution is 0.10 mol / L, and the pH of the acetic acid-sodium acetate buffer solution is 4.0; the concentration of the cerium-doped carbon nitride nanozyme is 0.05 mg / mL; and the concentration of TMB is 5 µmol / L.

5. The use of a cerium-doped graphite phase carbon nitride nanozyme as claimed in claim 1, characterized in that: The instrument parameters of the fluorescence spectrometer in step S3 and step S6 are: excitation wavelength 281 nm, emission wavelength 350-450 nm, excitation voltage 700 V, and slit width 5 nm.

6. The use of a cerium-doped graphite phase carbon nitride nanozyme as claimed in claim 1, characterized in that: The tetracycline in step S4 was replaced with penicillin G sodium, cephalosporin, ampicillin, amoxicillin, and chloramphenicol at a concentration of 4.0 µg / mL, and the experimental methods of steps S4-S7 were used to evaluate the effects of other antibiotics on the fluorescence intensity of the system and to investigate the selectivity of the established fluorescence detection method for tetracycline.

7. The use of a cerium-doped graphite-phase carbon nitride nanozyme as claimed in claim 1, characterized in that: For a specific experimental sample, the tetracycline content therein is detected and calculated using steps S1-S8. After adding tetracycline of different concentrations to the experimental sample, the experiment is continued according to the experimental method of steps S4-S7, the fluorescence change rate DF / F0 is calculated, and the DF / F0 value is substituted into the standard curve equation in step S8 to calculate the detection concentration of tetracycline. The ratio of the tetracycline detection concentration and the corresponding spiked concentration is the spiked recovery rate. The practicability of the detection method is verified by the spiked recovery rate.

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