A method for high-sensitivity electrochemical detection of niclosamide based on MOF / COF composite and a sensor

Abstract

This invention belongs to the field of electrochemical sensor technology and aims to solve the problems of low sensitivity, insufficient charge transport efficiency, and weak target enrichment ability of existing electrochemical detection methods for niclosamide. It provides a highly sensitive electrochemical detection method and sensor for niclosamide based on MOF / COF composite materials. The sensor uses a glassy carbon electrode modified with MOF / COF composite material as the working electrode, combined with an auxiliary electrode and a reference electrode to form a three-electrode system. It utilizes the synergistic effect of the high specific surface area and high catalytic activity of MOF and the good conductivity and ordered porous structure of COF to enhance the adsorption, enrichment, and electron transfer efficiency of niclosamide. The detection method achieves accurate detection of niclosamide by optimizing electrochemical test parameters and employing square wave voltammetry. This invention features a low detection limit, wide linear range, strong anti-interference ability, excellent stability and reproducibility, and can rapidly detect niclosamide in water, soil, fish, and tablets, possessing broad practical application value.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical sensor technology, specifically relating to a highly sensitive electrochemical detection method and sensor for niclosamide based on MOF / COF composite material, which is suitable for trace detection of niclosamide in water, food and other samples. Background Technology

[0002] Niclosamide is a widely used insecticide and anthelmintic, highly effective against snails and tapeworms, and is also used for snail control in water bodies and treatment of tapeworm infections in livestock and poultry. However, niclosamide has a certain degree of residual toxicity, and excessive residues in water and food can pose potential harm to the ecological environment and human health. Therefore, establishing a highly sensitive, rapid, and accurate method for detecting niclosamide is of great significance.

[0003] Currently, the main methods for detecting niclosamide include high-performance liquid chromatography (HPLC), gas chromatography (GC), spectrophotometry, and electrochemical detection. Among these, electrochemical detection has become a research hotspot for trace pollutant detection due to its advantages such as ease of operation, fast detection speed, low cost, and the ability to enable portable on-site detection.

[0004] Metal-organic frameworks (MOFs) are porous materials formed by the self-assembly of metal ions or metal clusters and organic ligands through coordination bonds. They have high specific surface area, precisely controllable pore size, and rich topological structures, giving them significant advantages in the adsorption and enrichment of target substances. Covalent organic frameworks (COFs), on the other hand, are crystalline porous materials formed by small organic molecules linked by strong covalent bonds. They possess highly ordered pore structures, good chemical stability, and conductivity, which can effectively promote charge transport.

[0005] In existing electrochemical detection techniques for niclosamide, single MOFs or their derived carbon materials are commonly used. However, the limited adsorption and enrichment capacity of single MOFs and their derived carbon materials leads to insufficient charge transport efficiency, making it difficult to achieve accurate detection of trace niclosamide. Furthermore, some detection methods suffer from narrow linear ranges, weak anti-interference capabilities, and poor stability, failing to meet the needs of trace niclosamide detection in real-world samples. Therefore, combining COFs with MOFs, which possess strong adsorption capabilities, becomes an effective means to overcome these technical shortcomings. Summary of the Invention

[0006] This invention aims to overcome the technical defects of existing electrochemical detection methods for niclosamide, such as low sensitivity, insufficient charge transport efficiency, weak target enrichment ability, and narrow linear range. It provides a highly sensitive electrochemical detection method and sensor for niclosamide based on MOF / COF composite materials, enabling rapid, accurate, and trace detection of niclosamide.

[0007] Technical solution

[0008] (1) To achieve the above objectives, the present invention adopts the following technical solution: the sensor consists of a working electrode, an auxiliary electrode and a reference electrode forming a three-electrode system; wherein, the working electrode is a glassy carbon electrode modified with MOF / COF composite material, the auxiliary electrode is a platinum wire electrode, and the reference electrode is a calomel electrode (SCE) or a silver / silver chloride electrode (Ag / AgCl).

[0009] (2) The preparation method of the MOF / COF composite material includes the following steps:

[0010] 1. Preparation of MOF materials: Metal salts and organic ligands are added to an organic solvent, ultrasonically dispersed, and then placed in a round-bottom flask. The mixture is reacted at 100–140 °C for 18–30 h. After the reaction, the mixture is naturally cooled to room temperature, centrifuged, washed, and vacuum dried to obtain MOF powder. The metal salt is one or more of zirconium chloride, copper nitrate, and ferric chloride; the organic ligand is one or more of 2-aminoterephthalic acid, trimesic acid, and benzoic acid; and the organic solvent is one or more of N,N-dimethylformamide and N-methylpyrrolidone. Subsequently, the prepared MOF material is placed in a tube furnace and calcined at high temperature under a nitrogen protective atmosphere to obtain MOF-derived carbon materials.

[0011] 2. Preparation of COF material: Using a solvothermal method, organic monomers are added to a mixed solvent, ultrasonically dissolved, and then a catalyst is added. The mixture is placed in a polytetrafluoroethylene reactor and reacted at 80–120 °C for 24–72 h. After centrifugation, washing, and vacuum drying, COF powder is obtained. The organic monomers are one or more of N,N,N′,N′-tetramethyl(4-aminophenyl)-1,4-phenylenediamine (TPDA) and 2,3-dihydroxyterephthalaldehyde (2,3-Dha). The mixed solvent is a mixture of 1,4-dioxane and dioxane (volume ratio 1:1), and the catalyst is an aqueous acetic acid solution.

[0012] 3. Preparation of MOF / COF composite material: The MOF-derived carbon powder obtained in step (1) and the COF powder obtained in step (2) were dispersed in deionized water and ultrasonically dispersed for 30-60 min to obtain a uniform dispersion of MOF-derived carbon and COF composite material. Then, they were mixed at a volume ratio of 1:1-5:1 to obtain the MOF / COF composite material. This composite material can fully utilize the synergistic effect of the high specific surface area and high catalytic activity of MOF and the good conductivity and ordered pore structure of COF to enhance the adsorption, enrichment and electron transfer efficiency of niclosamide.

[0013] (3) The method for preparing the working electrode includes the following steps:

[0014] 1. Pretreatment of glassy carbon electrode: Polish the glassy carbon electrode to a mirror finish with 0.3 μm and 0.05 μm alumina powder in sequence, then ultrasonically clean it with anhydrous ethanol and ultrapure water for 5-10 min respectively, and dry it with nitrogen gas for later use.

[0015] 2. Preparation of Modification Solution: MOF-derived carbon powder and COF powder were dispersed in deionized water and ultrasonically dispersed for 30–60 min to obtain a concentration of 0.5–2 mg / mL. -1 MOF and COF composite material dispersions were then ultrasonically mixed at a volume ratio of 1:1 to 5:1 to obtain MOF / COF composite materials.

[0016] 3. Electrode modification: Take 4-8 μL of the modification solution with a pipette and drop it onto the surface of the pretreated glassy carbon electrode. Dry it under an infrared lamp to obtain the MOF / COF composite material modified glassy carbon electrode.

[0017] (4) This method is based on the above-mentioned sensor and specifically includes the following steps:

[0018] 1. Plotting the standard curve:

[0019] 2. Prepare a series of niclosamide standard solutions with different concentrations, ranging from 1.0 × 10⁻⁶. -12 M-6.0×10 -6 M, with phosphate-buffered saline (PBS, pH 6.0–8.0) as the supporting electrolyte;

[0020] 3. Insert the three electrodes of the sensor into the above niclosamide standard solution and perform electrochemical testing using square wave voltammetry (SWV). Set the test parameters as follows: potential range of -0.5 to 0.3 V, amplitude of 25 mV, frequency of 15 Hz, and settling time of 2 s.

[0021] 4. Record the oxidation peak current values ​​corresponding to different concentrations of niclosamide standard solutions. Plot a standard curve with the logarithm of niclosamide concentration on the x-axis and the oxidation peak current value on the y-axis to obtain the linear regression equation.

[0022] 5. Take the samples to be tested (water, soil, fish, and niclosamide tablets), centrifuge and filter them, then dilute them to the appropriate concentration with phosphate buffer solution (PBS, pH=6.0-8.0);

[0023] 6. Insert the three electrodes of the sensor into the diluted sample solution, perform square wave voltammetry test according to the test parameters in step 1.2, and record the oxidation peak current value;

[0024] 7. Substitute the measured oxidation peak current value into the linear regression equation of the standard curve to calculate the concentration of niclosamide in the sample to be tested;

[0025] 8. Interference Experiment and Stability Test: During the detection process, common interfering substances (such as metal ions, other pesticides, organic matter, etc.) can be added to the sample solution to verify the sensor's anti-interference ability; the stability and reproducibility of the sensor can be verified by repeatedly testing the same concentration of niclosamide solution. Attached Figure Description

[0026] Figure 1 The XRD pattern of the material of this invention;

[0027] Figure 2 The SWV diagrams of the sensor of the present invention with respect to niclosamide are shown below, along with those of a glassy carbon electrode, a pure MOF-modified electrode, and a pure COF-modified electrode.

[0028] Figure 3 The SWV plots and linear calibration curves of the sensor of this invention for detecting different concentrations of niclosamide are shown below.

[0029] Figure 4 These are test diagrams for the anti-interference performance (A), long-term stability (B), reproducibility (C), and repeatability (D) of the sensor of this invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0031] Example 1: Preparation of MOF / COF composite materials

[0032] Preparation of MOF material (ZrO2@C): Zirconium chloride, benzoic acid, and meso-tetra(4-carboxyphenyl)porphyrin were dissolved in N,N-dimethylformamide. The solution was sonicated to ensure complete dissolution of all reactants, and the reaction was carried out at 120°C for 24 hours. The resulting product was washed several times with tetrahydrofuran and deionized water, and then dried in a vacuum oven to obtain a light purple PCN-222 solid powder. The obtained PCN-222 was placed in a tube furnace and calcined at high temperature under a nitrogen atmosphere to obtain ZrO2@C.

[0033] 2. Preparation of COF material (COF-TPDA): N,N,N′,N′-tetramethyl(4-aminophenyl)-1,4-phenylenediamine (TPDA) and 2,3-dihydroxyterephthalaldehyde (2,3-Dha) were dissolved in a mixed solution of 1,4-dioxane, o-dichlorobenzene, and acetic acid. The resulting mixture was then transferred to a polytetrafluoroethylene reactor and reacted at 120°C for 3 days. The product was washed with dimethyl sulfoxide and ethanol to obtain a brown crystalline powder, COF-TPDA.

[0034] 3. Preparation of MOF / COF composite materials: ZrO2@C and COF-TPDA were dispersed separately in deionized water to prepare solutions, which were then sonicated to completely dissolve them. Subsequently, the solutions were sonicated for 1 hour using a simple ultrasonic-assisted method at a ratio of 1:1 to 5:1 to prepare ZrO2@C / COF-TPDA composite materials.

[0035] Example 2: Preparation of the working electrode

[0036] 1. Pretreatment of glassy carbon electrode: Polish the glassy carbon electrode to a mirror finish with 0.3 μm and 0.05 μm alumina powder in sequence, then ultrasonically clean it with anhydrous ethanol and ultrapure water for 5-10 min respectively, and dry it with nitrogen gas for later use.

[0037] 2. Preparation of Modification Solution: MOF powder and COF powder were dispersed in deionized water and ultrasonically dispersed for 30–60 min to obtain a concentration of 0.5–2 mg / mL. -1 MOF and COF composite material dispersions were then ultrasonically mixed at a volume ratio of 1:1 to 5:1 to obtain MOF / COF composite materials.

[0038] 3. Electrode modification: Take 4-8 μL of the modification solution with a pipette and drop it onto the surface of the pretreated glassy carbon electrode. Dry it under an infrared lamp to obtain the MOF / COF composite material modified glassy carbon electrode.

[0039] Example 3: Sensor Assembly and Testing Performance

[0040] 1. Sensor assembly: Using the working electrode prepared in Example 2 as the working electrode, the platinum wire electrode as the auxiliary electrode, and the silver / silver chloride electrode as the reference electrode, a three-electrode system is formed, thus obtaining a highly sensitive electrochemical sensor of niclosamide based on MOF / COF composite material;

[0041] 2. Standard Curve Plotting: Niclosamide standard solutions with concentrations of 1 pM, 10 pM, 100 pM, 500 pM, 1 nM, 50 nM, 100 nM, 300 nM, 500 nM, 1 µM, 2 µM, 3 µM, 4 µM, 5 µM, and 6 µM were prepared, using phosphate buffer solution at pH 7.0 as the supporting electrolyte. A three-electrode method was used to test the standard solutions using square wave voltammetry. The oxidation peak current values ​​corresponding to each concentration were recorded. A standard curve was plotted with the logarithm of niclosamide concentration on the x-axis and the oxidation peak current value on the y-axis. The linear regression equations obtained were y = 2.52x + 11.08 and y = 46.86x - 68.06, with a correlation coefficient of R0. 2 =0.9934 and R 2=0.9902, detection limit is 0.51 pM;

[0042] 3. Anti-interference test: Add 100 times the concentration of ion interference substances (K⁺, Zn²⁺, Mg²⁺, Zn²⁺, NH₄⁺) to the above sample solution. + NO3 - The sensor was repeatedly tested with 5 times the concentration of similar interfering substances (nitroisocyanate (NYL), rafenib (RAX), p-nitrophenol (PNP), 2-chloro-4-nitrophenol (CNP), albendazole (ABZ) and praziquantel (PZQ)). The relative standard deviation of the oxidation peak current was ≤3%, indicating that the sensor has strong anti-interference ability.

[0043] 4. Stability Test: A 1.0 µM niclosamide standard solution was used for evaluation. The same sensor was used for 19 repeated measurements, and the relative standard deviation (RSD) of the oxidation peak current was 1.58%, indicating excellent repeatability. Nine parallel measurements were performed on nine separate sensors, and the relative standard deviation of the oxidation peak current was 1.18%, demonstrating good reproducibility. After refrigerating the sensor in a refrigerator for 50 days, the response current decreased by 5.12 μA, indicating excellent long-term stability.

[0044] Example 4: Performance Comparison of Different MOF / COF Mass Ratios

[0045] MOF / COF composite materials were prepared at mass ratios of 1:1, 2:1, 3:1, 4:1, and 5:1, respectively. The steps of Examples 2-3 were repeated, and the detection performance of the sensor was tested. The results showed that when the mass ratio of MOF to COF was 3:1, the sensor had the highest detection sensitivity and the best linear relationship. Too high or too low a mass ratio would weaken the synergistic effect between MOF and COF, leading to a decrease in detection performance.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A niclosamide electrochemical sensor based on MOF / COF composite material, characterized in that, The device includes a substrate electrode and a MOF / COF composite material layer modified on the surface of the substrate electrode. The MOF / COF composite material is a hybrid material formed by combining MOF and COF materials. The MOF material is ZrO2@C, and the COF material is COF-TPDA. The mass ratio of MOF to COF material in the MOF / COF composite material layer is 1:1 to 5:

1. The MOF / COF composite material is prepared by a simple ultrasound-assisted method. By leveraging the synergistic effect of MOF and COF, the adsorption capacity and electrochemical response performance of niclosamide are improved, achieving highly sensitive detection of niclosamide.

2. The sensor according to claim 1, characterized in that, The substrate electrode is one of glassy carbon electrode, ITO electrode, or gold electrode; the surface of the substrate electrode is pretreated, and the pretreatment steps are as follows: the substrate electrode is polished to a mirror finish with 1.0 μm, 0.3 μm, and 0.05 μm alumina powder in sequence, and then ultrasonically cleaned with anhydrous ethanol and ultrapure water for 5-15 min each, and dried with nitrogen gas for later use. The pretreatment is used to remove impurities on the electrode surface, reduce electrode impedance, and improve the bonding stability between the composite material layer and the electrode.

3. The sensor according to claim 1, characterized in that, The preparation method of the MOF / COF composite material includes the following steps: Step 1: Preparation of ZrO2@C (MOF material) by oil bath reflux: Zirconium chloride and N,N-dimethylformamide (DMF) were mixed and ultrasonicated for 15-20 min. Benzoic acid and methyl-4-tetra(4-carboxyphenyl)porphyrin were then added, and ultrasonication was continued for another 15-20 min until the system was homogeneous. The mixture was then heated at 120℃ for 24 h. After the reaction was completed, the mixture was naturally cooled to room temperature, and the product was collected by centrifugation. The product was washed repeatedly with N,N-dimethylformamide, tetrahydrofuran, and deionized water 3-5 times. The product was then dried under vacuum at 50℃ for 6-8 h to obtain light purple PCN-222 powder. Subsequently, the prepared MOF material was placed in a tube furnace and calcined at high temperature under a nitrogen protective atmosphere to obtain ZrO2@C material. Step 2: In-situ composite preparation of COF-TPDA (COF material) using a solvothermal method: N,N,N′,N′-tetramethyl(4-aminophenyl)-1,4-phenylenediamine (TPDA) and 2,3-dihydroxyterephthalaldehyde (2,3-Dha) were dissolved in a mixed solution of 1,4-dioxane, o-dichlorobenzene, and acetic acid. The resulting mixture was then transferred to a polytetrafluoroethylene reactor and reacted at 120°C for 3 days. The product was washed with dimethyl sulfoxide and ethanol to obtain brown crystalline powder COF-TPDA. Step 3: Disperse the MOF powder obtained in step (1) and the COF powder obtained in step (2) in deionized water and ultrasonically disperse for 30-60 min to obtain a uniform MOF and COF composite material dispersion; then mix them at a volume ratio of 1:1-5:1 to obtain the MOF / COF composite material.

4. The sensor according to claim 3, characterized in that, In step 1, the amount of zirconium chloride used is 60-70 mg, the total amount of N,N-dimethylformamide used is 60-70 mL, the amount of methyl-tetra(4-carboxyphenyl)porphyrin used is 200-240 mg, and the amount of benzoic acid used is 5-7 g; in step 2, the amount of N,N,N′,N′-tetramethyl(4-aminophenyl)-1,4-phenylenediamine used is 55-65 mg, the total amount of the mixed solution used is 20 mL, the amount of 2,3-dihydroxyterephthalaldehyde used is 25-30 mg, and the amount of acetic acid aqueous solution used is 2-5 mL.

5. The sensor according to claim 1, characterized in that, The MOF / COF composite material layer is prepared by drop coating. Specifically, MOF and COF composite materials are dispersed separately in deionized water and ultrasonically dispersed for 15-20 min until a uniform suspension is formed. The suspension is then ultrasonically assisted in composite formation according to a certain ratio. 5-10 μL of the suspension is drop-coated onto the pretreated substrate electrode surface and dried under an infrared lamp to form a film with a thickness of 5-15 μm. This film has good conductivity and stability, can efficiently capture niclosamide and produce a significant electrochemical response.

6. A highly sensitive electrochemical detection method for niclosamide based on the sensor described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step A: Sensor Activation: The electrochemical sensor is placed in a supporting electrolyte solution, forming a three-electrode system with the sensor as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Activation is performed using cyclic voltammetry, with a scan potential range of -0.5–0.3 V and a scan rate of 100 mV·s. -1 Scan for 5-10 cycles until the peak shape and peak current of the cyclic voltammetry curve stabilize. Step B: Standard curve plotting: The activated sensor is placed in a series of standard solutions of niclosamide with different concentrations, and the square wave voltammetry is used for detection. The oxidation peak current value of niclosamide is recorded. The standard curve is plotted with the concentration of niclosamide as the abscissa and the oxidation peak current value as the ordinate, and the linear regression equation is obtained. Step C: Sample detection: Place the activated sensor in the pretreated sample solution and use the same square wave voltammetry detection conditions as in Step B. Record the oxidation peak current value and substitute it into the linear regression equation obtained in Step B to calculate the content of niclosamide in the sample. The detection method utilizes the high specific surface area and excellent electrochemical performance of MOF / COF composite material to achieve highly sensitive and selective detection of niclosamide.

7. The detection method according to claim 6, characterized in that, The concentration range of the niclosamide standard solution is 1×10⁻ 12 -6×10⁻ 6 M, linear correlation coefficient R 2 With a detection limit of ≥0.99 and a detection limit of 0.51 pM (S / N=3), the detection sensitivity is improved by 1-2 orders of magnitude compared to single MOF or COF modified sensors, which is superior to existing electrochemical detection technologies for niclosamide.

8. The detection method according to claim 6, characterized in that, The samples to be tested include water samples, soil samples, biological samples, and tablet samples; the pretreatment steps for the sample solutions are as follows: take the sample to be tested, and at 8000-10000 r·min -1 Centrifuge for 10-15 min under the specified conditions, take the supernatant and filter it through a 0.22 μm filter membrane to remove impurities, then dilute it with a supporting electrolyte solution to a suitable concentration to obtain the sample solution to be tested. Pretreatment can effectively eliminate sample matrix interference and ensure detection accuracy.

9. The detection method according to claim 6, characterized in that, The selectivity of the detection method satisfies the following condition: the detection error is ≤5% in the presence of interfering substances at concentrations higher than niclosamide; the interfering substances include nitrophenolonitrile (NYL), rafenib (RAX), p-nitrophenol (PNP), 2-chloro-4-nitrophenol (CNP), albendazole (ABZ), and praziquantel (PZQ), as well as common metal ions (NH4⁺, K⁺, Zn). 2+ Mg 2+ SO4 2- NO3 - One or more of the following: ); and the detection method has good stability, with a relative standard deviation (RSD) of ≤3% for 10 consecutive tests.

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