CN112538347B

CN112538347B - Preparation method and application of nitrogen-doped carbon quantum dot-based fluorescent imprinting material

Info

Publication number: CN112538347B
Application number: CN202011296613.6A
Authority: CN
Inventors: 黄卫红; 吴长春; 倪晓霓; 杨文明; 曹云飞; 栾雨
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2020-11-18
Filing date: 2020-11-18
Publication date: 2022-04-26
Anticipated expiration: 2040-11-18
Also published as: CN112538347A

Abstract

The invention belongs to the technical field of detection material preparation, and relates to a preparation method and application of a nitrogen-doped carbon quantum dot-based fluorescent imprinting material. The method comprises the following steps: firstly, preparing nitrogen-doped carbon quantum dots, synthesizing silicon dioxide nanospheres, and then chemically modifying amino on the surface of the nitrogen-doped carbon quantum dots; and finally obtaining the nitrogen-doped carbon quantum dot-based fluorescent imprinted material. The carbon quantum dot prepared by the method has high quantum yield, and is easy to generate electron transfer with sulfadiazine to form stable hydrogen-like bond acting force. And secondly, forming complementary imprinting sites on the surface functional monomers of the silicon dioxide spheres by a sol-gel method, and combining the hydrogen-like bond action of lone pair electron nitrogen to obtain the molecular imprinting polymer so as to realize selective recognition of the molecular imprinting polymer. The imprinting material has an obvious core-shell structure consistent with the invention target; meanwhile, the invention combines the performance of the molecular imprinting material and the fluorescent response material, and is successfully applied to the high-efficiency detection of sulfadiazine.

Description

Preparation method and application of nitrogen-doped carbon quantum dot-based fluorescent imprinting material

Technical Field

The invention belongs to the technical field of detection material preparation, and particularly relates to a preparation method and application of a nitrogen-doped carbon quantum dot-based fluorescence imprinting sensor.

Background

Sulfadiazine (SDZ) is a middle-acting sulfonamide for systemic application, and is a broad-spectrum bacteriostatic agent. Because of the advantages of low cost, broad-spectrum bacteriostasis and the like, the SDZ is widely applied to the breeding industry as an anti-infective drug. Because of its long half-life, SDZ degrades very slowly in water, soil and cellular tissues, which makes sulfadiazine readily available for enrichment in animals. In daily life, if the animal products containing the sulfadiazine exceeding the standard are eaten for a long time, adverse reactions can be generated on systems such as urinary system, nerve and blood of people, and the health of the people is threatened. The most direct and effective method for controlling the SDZ residue is to establish a detection means with good accuracy, good repeatability and high sensitivity. Therefore, developing an efficient, low-cost analytical method to detect SDZ in environments and foods has become one of the hot spots of research. At present, methods for detecting SDZ are commonly used, such as high performance liquid chromatography, electrochemical method, gas chromatography-mass spectrometry, and the like. However, these methods have problems such as expensive equipment, complicated pretreatment, susceptibility to environmental influences, and poor reproducibility. Therefore, the research on a method for detecting sulfadiazine with high efficiency and low cost is very urgent and important.

In recent years, carbon Quantum Dots (QDs) have received much attention from the scientific community as fluorescent probes for fluorescence detection. Due to unique optical properties, ease of synthesis, good biocompatibility and low toxicity, environmentally friendly carbon quantum dots have been used to detect target molecules as fluorescent sensors. The surface defects of the quantum dots can be adjusted through the doping process, the structure, optical and physicochemical properties of the quantum dots are improved, and the fluorescence yield is improved. However, the lack of good selectivity is a major drawback of quantum dots, which limits their applications. To address this problem, quantum dots are combined with molecular imprinting techniques, imprinting polymers (MIPs) that have a specific response to a target.

The molecular imprinting technique is a highly selective technique that can form a template-shaped cavity by using the memory of a template molecule, and thus has received wide attention in the field of purification and selective separation. A highly cross-linked three-dimensional network structure is formed among the functional monomer, the cross-linking agent and the template molecule. After the elution of the template molecules, the MIPs obtain specific recognition sites matched with the shape and size of the target object so as to achieve the purpose of detecting the target object. Therefore, the combination of the molecularly imprinted polymer and the nitrogen-doped fluorescent sensor has the potential of detecting sulfadiazine in actual samples.

Disclosure of Invention

The invention provides a preparation method of a nitrogen-doped carbon quantum dot-based fluorescent imprinting material, which is used for synthesizing nitrogen-doped carbon quantum dots, solving the problem of low yield of the quantum dots and ensuring that nitrogen-doped carbon quantum has good responsiveness to a target object. And the detection of the actual sulfadiazine in the pork is realized by combining the molecularly imprinted polymer.

A preparation method of a nitrogen-doped carbon quantum dot-based fluorescence imprinting material comprises the following steps:

step 1, preparation of nitrogen-doped quantum dots:

placing citric acid, urea and distilled water into a stainless steel autoclave lined with polytetrafluoroethylene, stirring and dispersing, placing into a drying oven for heating reaction to obtain brown solution, centrifuging the obtained solution, filtering by using a filter membrane to remove large particles, and finally dialyzing the solution by using distilled water of a dialysis bag to obtain an N-CQDs solution;

step 2, silicon dioxide ball (SiO)₂) The preparation of (1):

firstly, adding tetraethyl orthosilicate (TEOS), ammonium hydroxide, ethanol and distilled water into a round-bottom flask, stirring, and continuously stirring at room temperature to perform a first-step reaction; then adding 3-Aminopropyltriethoxysilane (APTES) into the reaction system, and carrying out a second-step stirring reaction; washing the obtained substance with ethanol and distilled water, collecting white solid and vacuum drying; obtaining silicon dioxide ball powder;

step 3, preparation of imprinted polymer:

s1, mixing SiO₂Mixing APTES, N-CQD and ethanol, and carrying out a first-step stirring reaction to obtain a reaction solution 1;

s2, dissolving SDZ and NaOH solution in distilled water, stirring and dispersing uniformly, then mixing with the reaction solution 1 obtained in the step S1, and continuing stirring and reacting to obtain a reaction solution 2;

s3, adding TEOS, APTES and ammonium hydroxide into the reaction liquid 2, and stirring and reacting at room temperature to obtain a suspension; and the suspension was washed three times with methanol-acetic acid solution to remove the template molecules until no characteristic absorption peak of SDZ was detected in the solution by uv-vis spectroscopy, and then the solid particles were collected and dried in a vacuum oven to give imprinted polymer powders, denoted MIPs @ N-CQDs.

Preferably, in the step 1, the dosage ratio of the citric acid, the urea and the distilled water is 0.5-1.5 g: 1.5-4.5 g: 5-15 mL; stirring and dispersing for 10min, heating and reacting at 160-200 ℃ for 8-20 h.

Preferably, in step 2, the dosage ratio of tetraethyl orthosilicate (TEOS), 3-Aminopropyltriethoxysilane (APTES), ammonium hydroxide, ethanol and distilled water is 0.5-2 mL: 100-300. mu.L: 0.5-1.5 mL: 20-60 mL: 10-30 mL. When the solvent is centrifugally washed, the ratio of ethanol to distilled water is 1: 1; the reaction time of the first step is 8-20h, and the reaction time of the second step of stirring is 4-8 h; the vacuum drying temperature is 60 ℃, and the drying time is 10-20 h.

Preferably, in S1 of step 3, silica Spheres (SiO) are used₂) The dosage proportion of 3-aminopropyl triethoxysilane (APTES), N-CQD and ethanol is 50-150 mg: 50-150 μ L: 0.5-1.5 mL: 20-60 mL; the stirring reaction time of the first step is 2-6 h.

Preferably, in step 3S 2, the ratio of sulfadiazine, sodium hydroxide solution and distilled water is 100-200 mg: 50-100 μ L: 10-20mL, wherein the concentration of the oxyhydrogen solution is 1 mol/L; the stirring reaction time is 0.5-1 h.

Preferably, in step 3S 3, the ratio of the amounts of TEOS, APTES, and ammonium hydroxide is 0.5-1.5 mL: 1-2 mL: 1-2 mL; stirring and reacting for 8-20 h.

In steps S1, S2, and S3 of step 3, the usage ratio of silica spheres, sulfadiazine, and TEOS is: 50-150 mg: 100-200 mg: 0.5-1.5 mL.

In step 3S 3, the volume ratio of the methanol-acetic acid solution is 9: 1; the vacuum drying temperature is 60 ℃, and the drying time is 10-20 h.

Preferably, in step 3, the reaction is carried out at normal temperature.

The nitrogen-doped carbon quantum dot fluorescent imprinted material prepared by the invention is used for detecting sulfadiazine in pork.

In addition, in the preparation of non-imprinted polymers (denoted as NIPs @ N-CQDs), the same procedure as above was followed, except that the template molecule, sulfadiazine, was not added.

Drawings

FIG. 1 is a scanning electron microscope image and a projection electron microscope image of a sample prepared in example 2, (a) is a transmission pattern of quantum dots, (b) is a crystal plane pattern of quantum dots, (c) is a MIPs @ N-CQDs scan pattern, and (d) is a MIPs @ N-CQDs transmission pattern.

Fig. 2 is a fourier infrared graph of the sample prepared in example 2, and (a) is a fourier infrared graph of the quantum dots. (b) Wherein i is SiO₂Ii is a Fourier infrared plot of MIPs @ N-CQDs, iii is a Fourier infrared plot of NIPs @ N-CQDs, iv is a Fourier infrared plot of MIPs @ N-CQDs after elution.

Fig. 3 is an XPS scan of the quantum dots prepared in example 2.

FIG. 4 is a condition optimization study of MIPs @ N-CQDs prepared in example 2, (a) is a pH performance curve of MIPs @ N-CQDs, (b) is a stability performance curve of MIPs @ N-CQDs, and (c) is a response time curve of MIPs @ N-CQDs.

Fig. 5 is an ultraviolet absorption spectrum and a fluorescence spectrum of the quantum dot prepared in example 2.

FIG. 6 shows fluorescence studies of MIPs @ N-CQDs and NIPs @ N-CQDs prepared in example 2.

FIG. 7 is a selection study of MIPs @ N-CQDs and NIPs @ N-CQDs prepared in example 2.

Detailed Description

The invention is further described with reference to specific examples on the lower surface:

example 1:

step 1, preparation of nitrogen-doped quantum dots:

1g of (CA), 2g of urea, 10mL of distilled water were placed in a stainless steel autoclave (20mL) lined with polytetrafluoroethylene. Then, the mixture was heated in an oven set at 160 ℃ for 20 hours. The resulting solution was subjected to centrifugation (8500rpm, 10 minutes) and then filtered using a 0.22 μm membrane to remove large particles. Finally, the solution was dialyzed with a dialysis bag (dialysate of molecular weight 2000 Da) against distilled water for 24 hours to obtain N-CQDs solution.

Step 2 silicon dioxide ball SiO₂The preparation of (1):

first, 0.5mL of TEOS, 1mL of ammonium hydroxide, 20mL of ethanol, and 10mL of distilled water were added to a 100mL round-bottom flask, and dispersed with stirring for 10 minutes. The reaction was then continued at room temperature with stirring for 20 hours. Then 100. mu.L of APTES was added to the reaction system, and stirring was maintained for 8 hours. The product was washed 3 times with ethanol and distilled water, collected and dried under vacuum at 60 ℃ for 12 hours and reported as SiO₂。

Step 3 preparation of imprinted polymer:

first, 50mg of SiO are placed in a 100mL flask ₂100 μ L of APTES and 1mL of N-CQD were dispersed in 40mL of ethanol and stirred for 6 h. Second, 200mg of SDZ was dissolved in 20mL of distilled water and stirred for 10 minutes, and 100. mu.L of NaOH (1M) was added to the flask. Third, after 30 minutes, 1mL TEOS, 1.5mL APTES, 2mL ammonium hydroxide was charged into the flask and stirred at room temperature for 12 hours to obtain solid particles. Finally, the solid particles were washed three times with methanol-acetic acid solution (9: 1, v/v) to remove the template molecules until no characteristic absorption peak of SDZ was detected in the solution by uv-vis spectroscopy. The solid particles were then collected and dried in a vacuum oven at 60 ℃ for 12h to give MIPs @ N-CQDs powder.

At the same time, NIPs @ N-CQDs were prepared under the same procedure except that no template molecule SDZ was added.

Example 2:

step 1, preparation of nitrogen-doped quantum dots:

1g of (CA), 3g of urea, 10mL of distilled water were placed in a stainless steel autoclave (20mL) lined with polytetrafluoroethylene. Then, the mixture was heated in an oven set at 180 ℃ for 12 hours. The resulting solution was subjected to centrifugation (8500rpm, 10 minutes) and then filtered using a 0.22 μm membrane to remove large particles. Finally, the solution was dialyzed with a dialysis bag (dialysate of molecular weight 2000 Da) against distilled water for 24 hours to obtain N-CQDs solution.

Step 2 silicon dioxide ball SiO₂The preparation of (1):

first, 1mL of TEOS, 1mL of ammonium hydroxide, 40mL of ethanol, and 20mL of distilled water were added to a 100mL round-bottom flask, and dispersed with stirring for 10 minutes. The reaction was then continued at room temperature with stirring for 12 hours. Then 200. mu.L of APTES was added to the reaction system, and stirring was maintained for 6 hours. The product was washed 3 times with ethanol and distilled water, collected and dried under vacuum at 60 ℃ for 12 hours and reported as SiO₂。

Step 3 preparation of imprinted polymer:

first, in a 100mL flask, 100mg of SiO ₂100 μ L of APTES and 1mL of N-CQD were dispersed in 20mL of ethanol and stirred for 6 h. Second, 100mg SDZ was dissolved in 10mL distilled water and stirred for 10 minutes, 100. mu.L NaOH (1M) was added to the flask. Third, after 30 minutes, 1mL TEOS, 1mL APTES, and 1mL ammonium hydroxide were charged into the flask, and stirred at room temperature for 12 hours to obtain solid particles. Finally, the solid particles were washed three times with methanol-acetic acid solution (9: 1, v/v) to remove the template molecules until no characteristic absorption peak of SDZ was detected in the solution by uv-vis spectroscopy. The solid particles were then collected and dried in a vacuum oven at 60 ℃ for 12h to give MIPs @ N-CQDs powder.

Example 3:

step 1, preparation of nitrogen-doped quantum dots:

1.5g of (CA), 4.5g of urea, 15mL of distilled water were placed in a stainless steel autoclave (20mL) lined with polytetrafluoroethylene. Then, the mixture was heated in an oven set at 200 ℃ for 8 hours. The resulting solution was subjected to centrifugation (8500rpm, 10 minutes) and then filtered using a 0.22 μm membrane to remove large particles. Finally, the solution was dialyzed with a dialysis bag (dialysate of molecular weight 2000 Da) against distilled water for 24 hours to obtain N-CQDs solution.

Step 2 silicon dioxide ball SiO₂The preparation of (1):

first, 2mL of TEOS, 1.5mL of ammonium hydroxide, 60mL of ethanol, and 20mL of distilled water were added to a 100mL round-bottom flask, and dispersed with stirring for 10 minutes. However, the device is not suitable for use in a kitchenThe reaction was then continued at room temperature with stirring for 12 hours. Then 300. mu.L of APTES was added to the reaction system, and stirring was maintained for 6 hours. The product was washed 3 times with ethanol and distilled water, collected and dried under vacuum at 60 ℃ for 12 hours and reported as SiO₂。

Step 3 preparation of imprinted polymer:

first, in a 100mL flask, 100mg of SiO₂150 μ L of APTES and 1.5mL of N-CQDs were dispersed in 20mL of ethanol and stirred for 6 h. Second, 200mg of SDZ was dissolved in 20mL of distilled water and stirred for 10 minutes, and 100. mu.L of NaOH (1M) was added to the flask. Third, after 60 minutes, 0.5mL TEOS, 2mL APTES, and 1mL ammonium hydroxide were charged into the flask, and stirred at room temperature for 20 hours to obtain solid particles. Finally, the solid particles were washed three times with methanol-acetic acid solution (9: 1, v/v) to remove the template molecules until no characteristic absorption peak of SDZ was detected in the solution by uv-vis spectroscopy. The solid particles were then collected and dried in a vacuum oven at 60 ℃ for 12h to give MIPs @ N-CQDs powder.

FIG. 1 is a scanning electron micrograph and a projection electron micrograph of the sample prepared in example 2, as shown in FIG. a, in which N-CDs are spherical and have an average diameter of 4 nm. As shown in FIG. b, the lattice spacing of N-CQD is 0.24nm, corresponding to the (1120) crystal plane of graphite. The synthesized quantum dots are proved to have good dispersibility and morphology, which is beneficial to the subsequent imprinting process. The fluorescent material has a graphite structure, has a pi-conjugated structure, and is beneficial to energy transfer of quantum dots and quenching of fluorescence. As shown in FIG. c, d, MIPs @ N-CQDs can be found to have rough surfaces with an average diameter of about 200 nm. In addition, the MIPs @ N-CQDs have a spherical core-shell structure and a thin MIPs @ N-CQDs layer, and quantum dots are favorably and uniformly distributed on the surface of the silica spheres.

Fig. 2 is a fourier infrared graph of the sample prepared in example 2, and (a) is a fourier infrared graph of the quantum dots. As shown in FIG. 2a, at 3421cm^-1And 3215cm^-1Peaks at 1408cm, corresponding to O-H and N-H, respectively^-1Existence of peak(s) atThe tensile vibration of C-N is caused, and the nitrogen element is successfully doped. 1591cm^-1And 1688cm^-1The bands in the vicinity are associated with the stretching vibrations of C ═ O and C ═ C, respectively. These results indicate that nitrogen and epoxide exist on the surface of N-CQDs, and nitrogen element is successfully doped. (b) Wherein i is SiO₂Ii is a Fourier infrared plot of MIPs @ N-CQDs, iii is a Fourier infrared plot of NIPs @ N-CQDs, iv is a Fourier infrared plot of MIPs @ N-CQDs after elution. At 1046cm^-1、796cm^-1And 455cm^-1The characteristic peaks at (a) are respectively attributed to the symmetric bending vibration of Si-O-Si and Si-O. This indicates successful synthesis of silica. At 2938cm^-1And 1560cm^-1The nearby vibration peak is-NH₂And (4) stretching and vibrating, and indicating that the amino group is successfully modified on the surface of the silicon dioxide. The bond S ═ O is at 1728cm^-1The special vibration peaks at (A) indicate that SDZ is embedded in MIPs @ N-CQDs. As shown in curve iv, no characteristic peak of SDZ was found, indicating that the target had been well eluted. The result shows that MIPs @ N-CQDs @ CQDs @ SiO has been successfully synthesized₂@NH₃。

Fig. 3 is an XPS scan of the quantum dots prepared in example 2. Furthermore, as shown in fig. 3, the three peaks are 285.05eV, 399.85eV, 531.80eV respectively associated with C1s, N1s and O1s (fig. 3 a). As shown in fig. 3b, the peaks at 284.15eV, 284.99eV, 285.92eV and 288.15eV correspond to C ═ C, C ═ N, C — N and O — C ═ O. As shown in fig. 3C, the peaks for 399.26eV (pyridine nitrogen), 399.9eV (pyrrole nitrogen), 401.17eV (graphite nitrogen) correspond to C ═ N, C-N-C and C-N, respectively. The O1s scan curve (fig. 3d) shows peaks at 531.26eV and 532.60eV, which correspond to C ═ O and C-O-C/C-O-H. These results are similar to the infrared results, indicating successful doping with nitrogen and having a graphite-like structure.

FIG. 4 is a condition optimization study of MIPs @ N-CQDs prepared in example 2, (a) is a pH performance curve of MIPs @ N-CQDs where maximum quenching of fluorescence signal is observed around pH7.0 as shown in FIG. 4 a. therefore, pH7.0 is selected as the optimal experimental value for subsequent experiments. (b) Is a stability performance curve of MIPs @ N-CQDs, the fluorescence signal is basically not changed within one hour, which indicates MIPs @ N-CQDs @ CQDs @ SiO₂@NH₃Has good fluorescence stability. (c) Is MIPs @ N-CQDs response time curve. The fluorescence intensity of MIPs @ N-CQDs decreases rapidly in a short time in a 10. mu.M SDZ solution, which indicates that MIPs @ N-CQDs can respond rapidly to SDZ in solution.

Fig. 5 is an ultraviolet absorption spectrum and a fluorescence spectrum of the quantum dot prepared in example 2. The absorption band at 230nm can be attributed to the C-C pi-pi transition. The secondary peak at 345nm reflects the N-pi transition of the carbon-oxygen double bond on the surface of the N-CD. In addition, under the condition of adding sulfadiazine solutions with different concentrations, the absorption band at 230nm is enhanced, and the absorption band at 345nm is not changed. When the excitation wavelength was changed, the emission peak of N-CDs was hardly shifted, and the maximum emission peak at different excitation wavelengths was always kept at 430 nm.

FIG. 6 shows fluorescence studies of MIPs @ N-CQDs and NIPs @ N-CQDs prepared in example 2. As shown in FIG. 6(a, b), the fluorescence intensity of MIPs @ N-CQDs and NIPs decreases to different extents with increasing concentration of SDZ, but the fluorescence quenching degree of MIPs @ N-CQDs is much greater than that of NIPs at the same concentration. This indicates that the surface of MIPs @ N-CQDs have imprinted sites with similar shape and size to the target by the imprinting process. In addition, the fluorescence quenching degree of MIPs @ N-CQDs and NIPs @ N-CQDs has a good linear relationship with the concentration of SDZ in the range of 0-30. mu.M. Furthermore, as shown in FIG. 6(c, d), the linear fit of MIPs @ N-CQDs is F₀/F^-1＝0.0228[C]+0.0226, correlation coefficient (R)²) 0.9981 for Ksv 22800. By contrast, the linear fit of NIPs is F₀/F^-1＝0.00665[C]-0.0316，R²0.9967, and 6650 for Ksv. The blotting factor was calculated to be up to 3.43 with a minimum detection limit of 0.04. mu.M. These results indicate that the MIPs @ N-CQDs have the potential to sensitively detect SDZ fluorescent sensors.

FIG. 7 is a selection study of MIPs @ N-CQDs and NIPs @ N-CQDs prepared in example 2. As shown in FIG. 7b, the Ksv (MIPs @ N-CQDs) of SDZ is much higher than Sulfadimidine (SM)₂) Ksv (MIPs @ N-CQDs) of Sulfamethazine (SMZ) and Sulfamethoxazole (SMX) indicates that the fluorescence response ability of the sensor to SDZ is far greater than that of other analogues. In addition, the fluorescence response of MIPs @ N-CQDs to SDZ is shown in FIG. 7cComparison of SM₂The degree of the fluorescent response of SMZ and SMX was significant. And the fluorescence intensity of MIPs @ N-CQDs is changed to a much higher degree than that of NIPs @ N-CQDs. The results show that the synthesized MIPs @ N-CQDs have good selectivity in SDZ determination.

Description of the drawings: the above embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention; thus, while the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Claims

1. A preparation method of a nitrogen-doped carbon quantum dot-based fluorescence imprinting material is characterized by comprising the following steps:

step 1, preparation of nitrogen-doped quantum dots:

step 2, silicon dioxide ball SiO₂The preparation of (1):

firstly, adding tetraethyl orthosilicate TEOS, ammonium hydroxide, ethanol and distilled water into a round-bottom flask, stirring, and continuously stirring at room temperature to perform a first-step reaction; then adding 3-aminopropyltriethoxysilane APTES into the reaction system, and carrying out the second-step stirring reaction; washing the obtained substance with ethanol and distilled water, collecting white solid and vacuum drying; obtaining silicon dioxide ball powder;

step 3, preparation of imprinted polymer:

2. The method of claim 1, wherein: in the step 1, the dosage ratio of the citric acid, the urea and the distilled water is 0.5-1.5 g: 1.5-4.5 g: 5-15 mL; stirring and dispersing for 10min, heating and reacting at 160-200 ℃ for 8-20 h.

3. The method of claim 1, wherein: in step 2, the dosage ratio of tetraethyl orthosilicate (TEOS), 3-Aminopropyltriethoxysilane (APTES), ammonium hydroxide, ethanol and distilled water is 0.5-2 mL: 100-300. mu.L: 0.5-1.5 mL: 20-60 mL: 10-30 mL; when the solvent is centrifugally washed, the ratio of ethanol to distilled water is 1: 1; the reaction time of the first step is 8-20h, and the reaction time of the second step of stirring is 4-8 h; the vacuum drying temperature is 60 ℃, and the drying time is 10-20 h.

4. The method of claim 1, wherein: in S1 of step 3, silica Spheres (SiO)₂) The dosage proportion of 3-aminopropyl triethoxysilane (APTES), N-CQD and ethanol is 50-150 mg: 50-150 μ L: 0.5-1.5 mL: 20-60 mL; the stirring reaction time of the first step is 2-6 h.

5. The method of claim 1, wherein: in step 3S 2, the ratio of sulfadiazine, sodium hydroxide solution and distilled water is 100-200 mg: 50-100 μ L: 10-20mL, wherein the concentration of the oxyhydrogen solution is 1 mol/L; the stirring reaction time is 0.5-1 h.

6. The method of claim 1, wherein: in step 3, in S3, the dosage ratio of TEOS, APTES and ammonium hydroxide is 0.5-1.5 mL: 1-2 mL: 1-2 mL; stirring and reacting for 8-20 h.

7. The method of claim 1, wherein: in steps S1, S2, and S3 of step 3, the usage ratio of silica spheres, sulfadiazine, and TEOS is: 50-150 mg: 100-200 mg: 0.5-1.5 mL.

8. The method of claim 1, wherein: in step 3S 3, the volume ratio of the methanol-acetic acid solution is 9: 1; the vacuum drying temperature is 60 ℃, and the drying time is 10-20 h.

9. The method of claim 1, wherein: in step 3, the reaction is carried out at normal temperature.

10. Use of the nitrogen-doped carbon quantum dot-based fluorescent imprinted material prepared by the preparation method of any one of claims 1-9 for detecting sulfadiazine in pork.