PCN-224-coated MnO2 nano composite material as well as preparation method and application thereof

Abstract

The invention relates to a PCN-224-coated MnO2 nano composite material as well as a preparation method and application thereof, and belongs to the field of nano sensing materials. The existing compounding of a metal-organic framework and a metal oxide nano material has the problems of weak binding force, easily damaged structure, indefinite process parameters and the like, so that the signal response fluctuation of a sensing detection system is large, and the detection sensitivity is limited. Therefore, PCN-224 is dispersed in an MES buffer solution, a potassium permanganate solution is added for ultrasonic treatment, and precipitates are centrifugally collected and dispersed in ultrapure water to obtain a composite material; meanwhile, the preparation method of the PCN-224 is defined. The composite material prepared on the basis is used for constructing a nitrite detection sensor, and the invention further provides a detection method of nitrite in food. The material dispersity and stability can be improved, the detection sensitivity is improved, and the method is used for detecting nitrite in actual samples such as food.

Description

Technical Field

[0001] The present invention relates to the field of nanosensing materials, and more specifically to a PCN-224@MnO2 nanocomposite material and a preparation method and application thereof. Background Art

[0002] In the field of composite preparation of metal-organic frameworks (MOFs) and metal oxide nanomaterials, existing technologies often achieve loading through physical adsorption or in situ growth methods. However, due to weak binding forces in the physical adsorption method, the loaded metal oxide easily falls off the MOF surface, resulting in insufficient material stability. While the in situ growth method can enhance binding strength, it is difficult to control the reaction kinetics, which can easily lead to damage to the MOF framework structure or excessive thickness of the metal oxide loading layer. For example, the high surface energy of MnO2 nanosheets makes them prone to agglomeration during the loading process, resulting in insufficient exposure of active sites and a significant reduction in catalytic efficiency.

[0003] Furthermore, existing synthesis processes lack systematic optimization of parameter control in key steps, such as ultrasonic treatment and centrifugal purification. The wide range of selectable ultrasonic power, duration, and centrifugation conditions can easily lead to uneven product morphology or residual impurities, compromising the stability and reproducibility of material properties. This uncontrollable process not only increases experimental trial-and-error costs but also limits the scalable preparation of materials.

[0004] The above problems further lead to defects such as large signal response fluctuations and limited detection sensitivity in sensing detection systems based on such composite materials. For example, in nitrite detection, poor material dispersion will reduce the uniformity of the color development reaction, thereby affecting the accuracy of the absorbance ratio. Although the problem can be partially alleviated by adjusting the loading ratio or introducing surface modifiers, these methods often require complex steps or additional reagents, increasing the preparation cost and application difficulty. Therefore, developing a method for preparing nanocomposites with clear process parameters, uniform loading and stable structure has become a difficult problem that urgently needs to be broken through in this field. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0006] Another object of the present invention is to provide a PCN-224@MnO2 nanocomposite material, which can effectively inhibit the agglomeration of nanosheets by uniformly loading MnO2 nanosheets on the surface of PCN-224, and significantly improve the dispersibility and stability of the material. This composite material combines the high specific surface area of PCN-224 with the oxidase-like activity of MnO2, and exhibits enhanced catalytic efficiency in the process of catalyzing the oxidation of the chromogenic substrate TMB to oxTMB. At the same time, its unique structural characteristics optimize the response sensitivity and linear range of the color development reaction to nitrite, thereby supporting high-precision, low-detection limit colorimetric ratio detection, and can achieve visual rapid analysis through color changes. In addition, the material preparation process parameters are clear and reproducible, providing a reliable basis for the convenient detection of nitrite in actual samples.

[0007] In order to achieve these purposes and other advantages according to the present invention, a method for preparing a PCN-224@MnO2 nanocomposite material is provided, which comprises the following steps: S1: Disperse 0.1-10 mL of 0.5-5 mg / mL PCN-224 in MES buffer solution, add 0.1-10 mL of 1-10 mM potassium permanganate solution, and sonicate. S2: The mixed solution after ultrasonication was centrifuged, and the precipitate was collected and dispersed in ultrapure water to obtain a PCN-224@MnO2 composite material.

[0008] Preferably, the ultrasonic treatment power is 50-500 W, the frequency is 20-40 kHz, and the ultrasonic treatment time is 10-100 min.

[0009] Preferably, the centrifugal speed is 9000-10000 rpm and the centrifugal time is 20-30 min.

[0010] Preferably, the preparation method of PCN-224 comprises the following steps: 1) dissolving tetracarboxyphenylporphyrin, zirconium oxychloride octahydrate, and benzoic acid in N, N-dimethylformamide to form a mixed solution; the mass ratio of tetracarboxyphenylporphyrin, zirconium oxychloride octahydrate, and benzoic acid is 1:1-5:20-30; 2) Transfer the mixed solution to a round-bottom flask and react at 80-100°C for 5-10 h to obtain a purple mixture; 3) The purple mixture was centrifuged and washed with N, N-dimethylformamide until the supernatant was clear to obtain PCN-224.

[0011] A PCN-224@MnO2 nanocomposite material is prepared by the above preparation method.

[0012] A nitrite detection sensor based on PCN-224@MnO2 nanocomposite material, comprising: The PCN-224@MnO2 composite material has a concentration of 5-50 μg / mL; 3,3',5,5'-tetramethylbenzidine solution at a concentration of 1-10 mM; Acetic acid-sodium acetate buffer solution, with a concentration of 0.05-0.5 M and a pH of 2.5-5; PCN-224@MnO2 composite material, 3,3',5,5'-tetramethylbenzidine solution and the sample to be tested were added to the acetic acid-sodium acetate buffer solution. After incubation for 15-30 minutes, the absorbance ratio at 445 nm and 652 nm was measured by UV-visible spectroscopy. The nitrite concentration was calculated based on the standard curve using this ratio.

[0013] A method for detecting nitrite in food comprises the following steps: a) Mix the sample to be tested with a 1-10 mM hydroxylamine hydrochloride solution at a volume ratio of 1:1-5, heat in a 40-60°C water bath for 10-30 minutes, cool to room temperature, and centrifuge to remove the precipitate to obtain a supernatant; b) adding a 0.1-5 mM ethylenediaminetetraacetic acid solution to the supernatant in an amount of 0.5-2% of the volume of the supernatant, and allowing to stand for 5-15 minutes to obtain a static solution; c) The static solution, PCN-224@MnO2 composite material, and 3,3',5,5'-tetramethylbenzidine solution were added to an acetic acid-sodium acetate buffer solution. After incubation for 15-30 minutes, the absorbance ratio at 445 nm and 652 nm was measured by UV-visible spectroscopy. The nitrite content in the sample was calculated based on the linear relationship between the absorbance ratio and nitrite concentration.

[0014] Preferably, the following steps are further included between step a) and step b): The supernatant after centrifugation to remove the precipitate was mixed with a 0.1-2 mg / mL proteinase K solution at a volume ratio of 1:0.05-0.2, and incubated with shaking at 37-45°C for 20-40 minutes in 50-100 mM Tris-HCl buffer at pH 7.0-8.0; After incubation, heat the mixture to 95-100°C for 5-10 minutes to inactivate the protease. After cooling, centrifuge at 8000-12000 rpm for 5-15 minutes, collect the supernatant, and proceed to step b).

[0015] Preferably, in step c), the acetic acid-sodium acetate buffer solution further comprises sodium pyrophosphate at a concentration of 0.05-0.3 mM; The incubation process in step c) is carried out under light-shielding conditions, and the mixture is vortexed for 10-30 seconds every 5 minutes during the incubation period.

[0016] Preferably, after step b) and before step c), the method further comprises the following steps: The static liquid is mixed with polyamide resin powder with a particle size of 50-200 μm at a volume ratio of 1:0.1-0.5, shaken at 25-40° C. for 10-30 min, and then centrifuged at 8000-12000 rpm for 5-10 minutes, and the supernatant is collected as a purified liquid and entered into step c); The polyamide resin powder is pretreated by washing with 0.1-0.5 M hydrochloric acid solution, ultrapure water, 0.1-0.5 M sodium hydroxide solution and ultrapure water in sequence until neutral, and then vacuum drying at 60-80° C. for 2-4 h.

[0017] The present invention has at least the following beneficial effects: First, the present invention optimizes the in-situ loading process of MnO2 nanosheets on the PCN-224 surface, effectively inhibits the agglomeration of nanosheets, improves the material dispersibility and catalytic site accessibility, and enhances the stability and reuse potential of the composite material. Second, the present invention combines the high specific surface area of PCN-224 with the oxidase-like activity of MnO2 to significantly improve the oxidation efficiency of the chromogenic substrate TMB, providing a basis for high-sensitivity detection.

[0018] Third, the present invention combines quantitative analysis based on the absorbance ratio (445 nm / 652 nm) with visual detection of solution color changes, achieving a wide linear range (0-100 μM) and a low detection limit (0.23 μM), and is suitable for rapid detection of actual samples (such as sausages).

[0019] Fourth, clear optimization of ultrasonic treatment, centrifugation parameters and reaction conditions reduces the empirical dependence of the preparation process, ensures uniform material morphology and stable performance, and is conducive to large-scale preparation and application.

[0020] Other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1TEM images, fluorescence and UV-visible light of PCN-224 and PCN-224@MnO2; (a) (b) are TEM images of PCN-224 and PCN-224@MnO2, respectively; (c) (d) are fluorescence and UV-visible light spectra, respectively; Figure 2 This is the EDS spectrum analysis diagram of PCN-224@MnO2; Figure 3 (a) Fluorescence spectra of different nitrite concentrations; (b) Linear relationship between A445 / A652 and nitrite concentration; Figure 4 The results of the exploration of enzyme-like types of PCN-224@MnO2 are shown in Figure 1. (a) is the test of catalytic substrates of different materials; (b) is the catalytic test of PCN-224@MnO2 on different substrates. DETAILED DESCRIPTION

[0022] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0023] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0024] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0025] <Example 1> A method for preparing a PCN-224@MnO2 nanocomposite material comprises the following steps: 1) Synthesis of PCN-224: Tetracarboxyphenylporphyrin (TCPP, 0.05 g), zirconium oxychloride octahydrate (0.15 g), and benzoic acid (1.4 g) were dissolved in 50 mL of DMF, transferred to a round-bottom flask, and reacted in an oil bath at 90°C for 6 h to obtain a purple mixture. The mixture was purified by centrifugation and washed with DMF until the supernatant was clear to obtain PCN-224.

[0026] 2) Synthesis of PCN-224@MnO2: 1 mL of PCN-224 dispersion (1.6 mg / mL) was added to 7 mL of MES buffer (pH 6, 0.5 mM). After mixing, 0.8 mL of KMnO4 solution (5 mM) was added to the final volume of 12 mL. The mixture was sonicated (200 W, 40 kHz, 30 min) and centrifuged (9500 rpm, 25 min). The precipitate was then dispersed in ultrapure water and set aside.

[0027] The optical properties of the composite material were characterized by UV-visible absorption spectroscopy and fluorescence spectroscopy; the morphology and particle size of the material were characterized by TEM.

[0028] TEM shows that MnO2 nanosheets are uniformly loaded on the surface of PCN-224 ( Figure 1 ab); Fluorescence and UV-visible light results showed absorption peaks at 445 nm and 652 nm ( Figure 1 cd). EDS confirmed that the Mn element is evenly distributed ( Figure 2 ).

[0029] In this study, tetracarboxyphenylporphyrin (TCPP) was used as an organic ligand, zirconium oxychloride octahydrate (ZrOCl2·8H2O) was used as a metal source, and benzoic acid was used as a linker to self-assemble the metal-organic framework (MOF) PCN-224 in N,N-dimethylformamide (DMF) via a solvothermal reaction (90°C, 6 h). Benzoic acid regulates the Zr 4 ⁺The coordination rate with TCPP forms a stable porous structure.

[0030] PCN-224 was dispersed in MES buffer (pH 6) and potassium permanganate (KMnO4) was added. MnO2 nanosheets were in situ generated on the PCN-224 surface via an ultrasound-assisted redox reaction (KMnO4→MnO2). Ultrasonic treatment (200 W, 40 kHz, 30 min) promoted the uniform decomposition of KMnO4 and the directional deposition of MnO2 through cavitation, while preventing collapse of the PCN-224 framework. Subsequent centrifugation (9500 rpm, 25 min) removed unreacted impurities and ensured a pure loading layer.

[0031] Technical effects: Improved structural stability and dispersibility: TEM characterization shows that MnO2 nanosheets are uniformly loaded on the surface of PCN-224 ( Figure 1 ab), with no agglomeration. The porous structure of PCN-224 provides a high specific surface area support for MnO2, inhibiting the aggregation of MnO2 due to its high surface energy and significantly improving the material's dispersibility.

[0032] Enhanced catalytic activity: EDS spectrum ( Figure 2 ) confirmed the uniform distribution of the Mn element, indicating that MnO2 is tightly anchored to the MOF surface in the form of nanosheets. This structure combines the adsorption and enrichment capacity of PCN-224 with the oxidase-like activity of MnO2, resulting in higher catalytic efficiency in subsequent applications, such as the oxidation of TMB.

[0033] Process controllability and reproducibility: By optimizing ultrasonic power (200 W), centrifugation parameters (9500 rpm), and reaction pH (MES buffer pH 6), the problem of uneven morphology caused by a wide range of parameters in traditional loading processes was resolved, ensuring consistent performance between material batches and laying the foundation for large-scale preparation.

[0034] Optical property verification: UV-visible spectroscopy ( Figure 1 d) The composite material has characteristic absorption peaks at 445 nm and 652 nm, and the fluorescence spectrum ( Figure 1 c) It shows that the fluorescence characteristics of PCN-224 are regularly quenched due to MnO2 loading, which indirectly proves the effective combination of the two and provides a signal basis for subsequent colorimetric detection.

[0035] <Example 2> Sensitivity test of nitrite detection sensor Construction of detection system: PCN-224@MnO2 composite material (17 μg / mL) and TMB solution (5 mM, 20uL) were added to NaAc-HAc buffer (pH 4, 0.1 M) with a total volume of 2 mL.

[0036] Standard curve drawing: different concentrations of nitrite (1, 3, 5, 12.5, 25, 50, 75, 100, 125, 150 μM) were added, and the absorbance ratio at 445 nm and 652 nm was measured after incubation for 20 min.

[0037] Fluorescence spectra of different nitrite concentrations are shown in Figure 2. Figure 3 (a) The linear relationship between A445 / A652 and nitrite concentration is shown in Figure 3 The results showed that the linear range was 0-100 μM and the detection limit was 0.23 μM.

[0038] Actual sample test: After sausage samples were pretreated with hydroxylamine hydrochloride and ethylenediaminetetraacetic acid, the nitrite content was measured to be 34.5 μg / kg, with a recovery rate of 99.27%-105.00% (Table 1) Table 1 Actual sample testing The sensor demonstrated a linear range of 0-100 μM for phytic acid detection, with a detection limit of 0.23 μM. The sensor was applied to the detection of nitrite in sausages, achieving recoveries of 99.27%-105.00%. This translates to a nitrite content of 34.5 μg / kg, significantly lower than the recommended nitrite content of 0.15 g / kg and the residual content of 30 mg / kg specified in the Hygienic Standard for the Use of Food Additives (GB2706-2007). These results demonstrate the ability of the PCN-224@MnO2+TMB sensor system to detect nitrite in real-world samples.

[0039] <Example 3> Exploration of enzyme-like species of PCN-224@MnO2 1. Experimental Material Preparation: Prepare PCN-224@MnO2 composite material according to the method in Example 1. Prepare a 5 mM 3,3',5,5'-tetramethylbenzidine (TMB) solution, an o-phenylenediamine (OPD) solution, and an acetic acid-sodium acetate (NaAc-HAc) buffer solution at a pH of 4 and a 0.1 M concentration.

[0040] 2. Experimental grouping and reaction system construction: Multiple reaction groups were set up, namely PCN-224@MnO2+TMB group, PCN-224+TMB group, PCN-224@MnO2 group, TMB group, and PCN-224+TMB group.

[0041] In the PCN-224@MnO2+TMB group, 20 μL of 5 mM TMB solution was added to the PCN-224@MnO2 composite dispersion at a concentration of 17 μg / mL, and then acetic acid-sodium acetate buffer was added to a total volume of 2 mL; In the PCN-224+TMB group, the same amount of TMB solution and buffer solution were added to the PCN-224 dispersion with appropriate concentration (the concentration was consistent with the PCN-224 concentration in PCN-224@MnO2); The PCN-224@MnO2 group consisted of a dispersion of PCN-224@MnO2 composite material with acetic acid-sodium acetate buffer added; the TMB group consisted of 20 μL of 5 mM TMB solution with acetic acid-sodium acetate buffer added, with a total volume of 2 mL; For the OPD group, 20 μL of 5 mM OPD solution was added with acetic acid-sodium acetate buffer to a total volume of 2 mL.

[0042] 3. Reaction and Spectral Measurement: Mix all reaction solutions thoroughly and incubate for 20 min under the same conditions. After incubation, perform a UV-Vis spectrometer to scan the spectra of each reaction solution at a wavelength of 300-800 nm. Record the absorbance changes of each reaction solution within this wavelength range.

[0043] 4. Result analysis: Figure 4 It can be seen that the PCN-224@MnO2+TMB group exhibited a significantly different absorbance change trend at a specific wavelength from the other groups. This indicates that PCN-224@MnO2 has a unique catalytic effect on the oxidation reaction of TMB, which is significantly different from the presence of PCN-224 alone and other control conditions. This further proves that PCN-224@MnO2 has oxidase-like activity and that this activity plays an important role in catalyzing the oxidation reaction of TMB. At the same time, compared with the spectral curve of the OPD group, the specific catalytic effect of PCN-224@MnO2 on TMB can be more clearly seen, providing a strong basis for determining the enzyme-like type of PCN-224@MnO2.

[0044] <Example 4> A method for detecting nitrite in food comprises the following steps: 1) Sample pretreatment: 1 g of sausage sample was mixed with 5 mL of hydroxylamine hydrochloride solution (5 mM) at a volume ratio of 1:2. The mixture was heated in a 50°C water bath for 15 min. After cooling, the mixture was centrifuged at 10,000 rpm for 10 min, and the supernatant was collected.

[0045] 2) EDTA treatment: Add ethylenediaminetetraacetic acid (EDTA, 1 mM, 1% of the supernatant volume) to the supernatant and let it stand for 10 min to obtain a static solution.

[0046] 3) Detection reaction: The static solution, PCN-224@MnO2 composite material (17 μg / mL), and TMB solution (5 mM, 20 μL) were added to acetic acid-sodium acetate buffer (pH 4.0, 0.2 M) to a total volume of 2 mL and incubated in the dark for 20 min.

[0047] Absorbance determination: The absorbance ratio at 445 nm and 652 nm was measured. The nitrite concentration was calculated based on the standard curve to be 28.4 μM, with a recovery rate of 98.5%.

[0048] Centrifugation can remove precipitates (such as proteins, fats and other macromolecular impurities) to obtain a clear supernatant. Ethylenediaminetetraacetic acid (EDTA) forms stable complexes with metal ions (such as Fe³⁺, Cu²⁺, etc.) in the supernatant, blocking the catalytic effect of metal ions on the TMB oxidation reaction and avoiding false positive signals. The oxidase-like activity of PCN-224@MnO2 catalyzes the oxidation of TMB to oxTMB (blue product), producing a characteristic absorption peak at 652 nm. Residual nitrite reacts with oxTMB under acidic conditions (pH 4.0) to form a diazonium compound, resulting in an increase in absorbance at 445 nm and a decrease in absorbance at 652 nm. NO2 can be quantified by the ratio (A445 / A652). - concentration.

[0049] Technical effect: High specificity and anti-interference: Double treatment with hydroxylamine hydrochloride and EDTA effectively eliminates interference from protein, fat and metal ions in food matrices, ensuring the reliability of test results.

[0050] Sensitivity and accuracy: The nitrite content in sausage was measured to be 28.4 μM, with a recovery rate of 98.5%. Compared with the national standard method (GB 5009.33-2016), the error was <5%, verifying the accuracy of the method.

[0051] Rapid visual detection: incubation time is shortened to 20 min, and the solution color changes with NO2 - The concentration gradient change (colorless → light blue → blue-yellow) can support semi-quantitative visual judgment.

[0052] Low detection limit and wide linear range: The detection limit is as low as 0.23 μM, and the linear range covers 0-100 μM (R²=0.998), meeting the warning requirements for excessive nitrite residues in food (30 mg / kg≈435 μM).

[0053] <Example 5> A method for detecting nitrite in food comprises the following steps: 1) Sample pretreatment: Sausage homogenate was mixed with hydroxylamine hydrochloride (10 mM, volume ratio 1:3), incubated in a 60°C water bath for 20 min, and centrifuged to obtain the supernatant.

[0054] 2) Enzymatic hydrolysis: Add proteinase K (1 mg / mL, 1:0.1 volume ratio) to the supernatant in Tris-HCl buffer (pH 7.5, 100 mM) and incubate at 40°C with shaking for 30 min. Inactivate at 95°C for 10 min, centrifuge, and collect the supernatant.

[0055] 3) EDTA treatment: Add EDTA (2 mM, 1.5% by volume) and let it stand for 15 minutes.

[0056] 4) Detection reaction: The treated solution, PCN-224@MnO2 composite material (20 μg / mL, 150 μL), and TMB solution (8 mM, 25 μL) were added to acetic acid-sodium acetate buffer (pH 3.5, 0.3 M) containing sodium pyrophosphate (0.2 mM), and incubated in the dark for 25 minutes, with vortexing for 20 seconds every 5 minutes.

[0057] Result analysis: The RSD of the measured nitrite concentration was 3.2%, with strong anti-interference ability and a recovery rate of 102.3%.

[0058] Proteinase K in Tris-HCl buffer (pH 7.5) efficiently degrades proteins in the sample, eliminating nonspecific adsorption of proteins to the active sites of the nanocomposite and reducing false-positive signals. Sodium pyrophosphate (0.2 mM) inhibits nanocomposite aggregation through electrostatic shielding, maintaining exposure of catalytic active sites while also buffering the pH of the system and enhancing reaction stability. Incubation in the dark prevents spontaneous oxidation of TMB under light, reducing background noise. Vortexing (20 seconds) every 5 minutes ensures thorough mixing of the reactants, improving color development uniformity and signal consistency.

[0059] Technical effect: High anti-interference and precision: Proteinase K treatment reduces protein degradation to >95%. Combined with EDTA chelation, the RSD is as low as 3.2%, significantly better than traditional methods (RSD>10%), meeting the testing needs of complex food samples.

[0060] Sensitivity and Accuracy: The spiked recovery reached 102.3%, with a deviation of <3% compared with the national standard method (GB 5009.33-2016), validating the accuracy of the method. The detection limit was 0.20 μM, covering the trace detection range of nitrite residues in food.

[0061] Operational convenience and stability: The addition of sodium pyrophosphate improves the dispersibility of the composite material by 30% and the catalytic efficiency by 20%. The light-shielding and vortex design shortens the incubation time to 25 minutes, supporting high-throughput detection.

[0062] Broad applicability: The method was successfully applied to high-protein, high-fat sausage samples with stable recoveries (98.5%-105.0%), demonstrating its strong adaptability to diverse food matrices.

[0063] <Example 6> A method for detecting nitrite in food comprises the following steps: 1) Sample pretreatment: Sausage homogenate was mixed with hydroxylamine hydrochloride (10 mM, volume ratio 1:3), incubated in a 60°C water bath for 20 min, and centrifuged. The supernatant was collected.

[0064] 2) Enzymatic hydrolysis: Add proteinase K (1 mg / mL, 1:0.1 volume ratio) to the supernatant in Tris-HCl buffer (pH 7.5, 100 mM) and incubate at 40°C with shaking for 30 min. Inactivate at 95°C for 10 min, centrifuge, and collect the supernatant.

[0065] 3) EDTA treatment: Add EDTA (2 mM, 1.5% by volume) and let it stand for 15 min.

[0066] 4) Resin purification: The standing liquid was mixed with pretreated polyamide resin powder (particle size 100 μm, volume ratio 1:0.3), shaken at 35°C for 20 minutes, centrifuged at 12,000 rpm for 8 minutes, and the purified liquid was collected.

[0067] 5) Detection reaction: The purified solution, PCN-224@MnO2 composite material (40 μg / mL, 250 μL), and TMB solution (10 mM, 30 μL) were added to acetic acid-sodium acetate buffer (pH 2.8, 0.4 M) and incubated in the dark for 30 min.

[0068] Test results: The detection limit of nitrite was as low as 0.18 μM, the actual sample recovery rate was 99.8%, and the RSD was <2%, proving that the purification step effectively removed impurity interference.

[0069] Polyamide resins adsorb organic interfering substances such as pigments, polyphenols, and lipids in samples through hydrophobic interactions and hydrogen bonding. The pretreated resin (after acid and base washing) exhibits high adsorption capacity, effectively removing impurities from complex food matrices, reducing background signal and improving detection sensitivity.

[0070] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a PCN-224@MnO2 nanocomposite material, characterized in that: The following steps are involved: S1: Disperse 0.1-10 mL of 0.5-5 mg / mL PCN-224 in MES buffer solution, add 0.1-10 mL of 1-10 mM potassium permanganate solution, and sonicate. S2: The mixed solution after ultrasonication was centrifuged, and the precipitate was collected and dispersed in ultrapure water to obtain a PCN-224@MnO2 composite material.

2. The method for preparing the PCN-224@MnO2 nanocomposite material according to claim 1, wherein The power of ultrasonic treatment is 50-500 W, the frequency is 20-40 kHz, and the ultrasonic treatment time is 10-100 min.

3. The method for preparing the PCN-224@MnO2 nanocomposite material according to claim 1, wherein The centrifugal speed is 9000-10000 rpm and the centrifugation time is 20-30 min.

4. The method for preparing the PCN-224@MnO2 nanocomposite material according to claim 1, wherein The preparation method of PCN-224 comprises the following steps: 1) dissolving tetracarboxyphenylporphyrin, zirconium oxychloride octahydrate, and benzoic acid in N, N-dimethylformamide to form a mixed solution; the mass ratio of tetracarboxyphenylporphyrin, zirconium oxychloride octahydrate, and benzoic acid is 1:1-5:20-30; 2) Transfer the mixed solution to a round-bottom flask and react at 80-100°C for 5-10 h to obtain a purple mixture; 3) The purple mixture was centrifuged and washed with N, N-dimethylformamide until the supernatant was clear to obtain PCN-224.

5. A PCN-224@MnO2 nanocomposite material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 4.

6. A nitrite detection sensor based on PCN-224@MnO2 nanocomposite material, characterized in that: include: The PCN-224@MnO2 composite material according to claim 5, wherein the concentration is 5-50 μg / mL; 3,3',5,5'-tetramethylbenzidine solution at a concentration of 1-10 mM; Acetic acid-sodium acetate buffer solution, with a concentration of 0.05-0.5 M and a pH of 2.5-5; PCN-224@MnO2 composite material, 3,3',5,5'-tetramethylbenzidine solution and the sample to be tested were added to the acetic acid-sodium acetate buffer solution. After incubation for 15-30 min, the absorbance ratio at 445 nm and 652 nm was measured by UV-visible spectroscopy. The nitrite concentration was calculated based on the standard curve using this ratio.

7. A method for detecting nitrite in food, characterized in that: The following steps are involved: a) Mix the sample to be tested with a 1-10 mM hydroxylamine hydrochloride solution at a volume ratio of 1:1-5, heat in a 40-60°C water bath for 10-30 minutes, cool to room temperature, and centrifuge to remove the precipitate to obtain a supernatant; b) adding a 0.1-5 mM disodium edetate solution to the supernatant in an amount of 0.5-2% of the volume of the supernatant, and allowing the mixture to stand for 5-15 minutes to obtain a static solution; c) The static solution, PCN-224@MnO2 composite material, and 3,3',5,5'-tetramethylbenzidine solution were added to an acetic acid-sodium acetate buffer solution. After incubation for 15-30 minutes, the absorbance ratio at 445 nm and 652 nm was measured by UV-visible spectroscopy. The nitrite content in the sample was calculated based on the linear relationship between the absorbance ratio and nitrite concentration.

8. The method for detecting nitrite in food according to claim 7, wherein The following steps are also included between step a) and step b): The supernatant after centrifugation to remove the precipitate was mixed with a 0.1-2 mg / mL proteinase K solution at a volume ratio of 1:0.05-0.2, and incubated with shaking at 37-45°C for 20-40 minutes in 50-100 mM Tris-HCl buffer at pH 7.0-8.0; After incubation, heat the mixture to 95-100°C for 5-10 minutes to inactivate the protease. After cooling, centrifuge at 8000-12000 rpm for 5-15 minutes, collect the supernatant, and proceed to step b).

9. The method for detecting nitrite in food according to claim 8, wherein In step c), the acetic acid-sodium acetate buffer solution further comprises sodium pyrophosphate at a concentration of 0.05-0.3 mM; The incubation process in step c) is carried out under light-shielding conditions, and vortexing is performed for 10-30 seconds every 5 minutes during the incubation period.

10. The method for detecting nitrite in food according to claim 8, wherein: After step b) and before step c), the method further comprises the following steps: The static liquid is mixed with polyamide resin powder with a particle size of 50-200 μm at a volume ratio of 1:0.1-0.5, shaken at 25-40° C. for 10-30 minutes, and then centrifuged at 8000-12000 rpm for 5-10 minutes, and the supernatant is collected as a purified liquid and entered into step c); The polyamide resin powder is pretreated by washing with 0.1-0.5 M hydrochloric acid solution, ultrapure water, 0.1-0.5 M sodium hydroxide solution and ultrapure water in sequence until neutral, and then vacuum drying at 60-80° C. for 2-4 hours.

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