Covalent organic framework-based Fe3O4 (at) COF electrochemical sensor, preparation method and application

Abstract

The embodiment of the invention provides a Fe3O4 (at) COF electrochemical sensor based on a covalent organic framework, and a preparation method and application thereof. The electrochemical sensor comprises a base electrode with the surface modified with a solid film; the solid film is a Fe3O4 (at) COF composite material; the Fe3O4-coated COF composite material comprises an inner core formed by ferroferric oxide with a porous structure and a COF shell layer attached to the surface of the inner core, the COF shell layer is a covalent organic framework layer formed by copolymerization of an aromatic aldehyde compound and a polyamino aromatic compound. According to the Fe3O4 (at) COF electrochemical sensor based on the covalent organic framework, the preparation method and the application provided by the invention, quinolone antibiotic molecules such as norfloxacin and the like can be detected, and the detection limit can reach 1.927 * 10 <-13 > mol / L; and the method can be widely applied to detection of quinolone antibiotics such as norfloxacin in milk and environmental water samples.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical sensing detection, and in particular to a covalent organic framework porous Fe3O4 electrochemical sensor for detecting norfloxacin and a preparation method thereof. Background Art

[0002] Norfloxacin is a third-generation fluoroquinolone antibiotic and one of the most widely used fluoroquinolone antibiotics. Norfloxacin has low metabolic activity in humans and animals, resulting in 40–90% of its active metabolites being released into the environment through domestic sewage and aquaculture wastewater. In recent years, norfloxacin has been frequently detected in various aquatic environments, even in drinking water. Antibiotics in aquatic environments can cause imbalances in microbial populations and even induce the development of drug-resistant genes. Furthermore, they accumulate in the food chain and enter the human body, where they can induce the development of drug-resistant genes. Their mechanism of action is to inhibit bacterial DNA helicase, thereby inhibiting DNA replication and transcription, leading to bacterial death. Drug-resistant bacteria may also harbor resistance plasmids, which can be transferred between different bacterial species and strains, posing a significant threat to the prevention and control of infectious diseases.

[0003] Currently, the main methods for detecting norfloxacin are Raman scattering, enzyme-linked reaction (ELR), and liquid chromatography. Raman scattering confirms the presence of norfloxacin by comparing its spectra to standards and can quantitatively detect residues above 1 mg / kg. However, its sensitivity is limited, with a limit of detection (LOD) of only ppm. ELR immobilizes a norfloxacin-carrier protein conjugate on a microplate surface, measures the absorbance (OD) using a microplate reader, and calculates the norfloxacin concentration using a standard curve. This method can quantitatively detect residues between 1 and 10 mg / kg. However, due to the structural similarity of norfloxacin to other quinolone antibiotics (such as ciprofloxacin and ofloxacin), it is highly susceptible to antibody cross-reactions, resulting in false-positive or false-negative results. Liquid chromatography detects the presence of norfloxacin based on its UV absorption (maximum absorption wavelength approximately 278 nm), but the cost of LC instrumentation and maintenance is high, making it unsuitable for small laboratories or on-site testing. In contrast, electrochemical technology has attracted widespread attention due to its simple operation, fast analysis speed, low cost, high sensitivity and accuracy. Summary of the Invention

[0004] Aiming at the technical problems existing in the prior art, in order to solve the technical problems of low sensitivity, low precision, high cost and complicated operation of the detection method for norfloxacin in the prior art, a Fe3O4@COF electrochemical sensor based on a covalent organic framework, a preparation method and application are provided.

[0005] In a first aspect, the present invention provides a Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising: a base electrode whose surface is modified with a solid film; the solid film is a Fe3O4@COF composite material; the Fe3O4@COF composite material comprises: a core composed of ferrosoferric oxide with a porous structure and a COF shell layer attached to the surface of the core; the COF shell layer is a covalent organic framework layer formed by copolymerization of an aromatic aldehyde compound and a polyamino aromatic compound.

[0006] Preferably, the aromatic aldehyde compound is one or more of dimethoxyterephthalaldehyde, terephthalaldehyde, benzaldehyde, salicylaldehyde and vanillin; the polyamino aromatic compound is one or more of 1,3,5-tris(4-aminophenyl)benzene, p-phenylenediamine and 2,4,6-triaminopyrimidine.

[0007] Preferably, the molar ratio of the aromatic aldehyde compound to the polyamino aromatic compound is 1:(1-2).

[0008] Preferably, the mesopore diameter of the ferrosoferric oxide is 20-50 nm.

[0009] In a second aspect, the present invention further provides a method for preparing the Fe3O4@COF electrochemical sensor based on the covalent organic framework as described above, comprising the following steps: Preparation of Fe3O4 nanoparticles; Dissolving an aromatic aldehyde compound and a polyamino aromatic compound in a solvent to form a mixed solution; adding the Fe3O4 nanoparticles to the mixed solution, and performing ultrasonic treatment under the action of a catalyst to prepare a Fe3O4@COF composite material; The Fe3O4@COF composite material is drop-coated on the surface of the electrode to form a solid film to obtain a finished product.

[0010] Preferably, in the step of preparing Fe3O4 nanoparticles, the preparation method of Fe3O4 nanoparticles includes: Dissolving ferrous salt and aluminum salt in distilled water, adding ammonia water and mixing well to form a reaction solution, subjecting the reaction solution to an oxidation-reduction reaction at high temperature, and performing ultrasonic treatment to obtain a suspension; The magnetic precipitate phase in the suspension is separated by magnetic separation, and the magnetic precipitate phase is dried and nano-scale crushed to obtain the Fe3O4 nanoparticles.

[0011] Preferably, the mass ratio of the ferrous salt, the aluminum salt and the ammonia solution is 2:(2-3):(1-10); and the temperature of the redox reaction is 50-60°C.

[0012] In a third aspect, the present invention further provides a use of the Fe3O4@COF electrochemical sensor based on a covalent organic framework as described above in the detection of norfloxacin.

[0013] Preferably, 9. The application according to claim 8, characterized in that the application method comprises: Placing a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode in an electrolytic cell containing an electrolyte; the working electrode is the Fe3O4@COF electrochemical sensor; Configuration 10 -12 ~10 -4 M concentration gradient of norfloxacin standard solution; Differential pulse voltammetry was used to detect the oxidation peak current values of norfloxacin standard solutions with different concentration gradients. A linear regression equation was obtained by performing a linear regression between the oxidation peak current value I and the concentration C. A certain amount of sample was placed in the electrolytic cell, and the oxidation peak current value of the sample was detected by differential pulse voltammetry. The concentration of norfloxacin in the sample was calculated by the following formula (1): C=(Ib) / k(1) Preferably, the electrolyte in the electrolytic cell comprises a PBS buffer solution with a volume ratio of (4-5):1 and a potassium ferricyanide solution with a molar concentration of 3-5 mmol / L.

[0014] The beneficial effects of the present invention are: The Fe3O4@COF electrochemical sensor provided by the present invention is an electrode composed of a solid film formed by modifying the surface of a base electrode with a layer of Fe3O4@COF composite material. The Fe3O4@COF composite material has a core of ferroferric oxide with high catalytic activity and a porous structure, and an outer shell composed of a covalent organic skeleton formed by a covalent polycondensation reaction of aromatic aldehyde compounds and polyamino aromatic compounds. The Fe3O4 core provides a rich Fe 2+ / Fe 3+The redox active site will produce reactive oxygen species (ROS) during the detection process, which can efficiently oxidize and degrade quinolone antibiotic molecules such as norfloxacin. The COF outer shell forms a highly ordered two-dimensional layered structure through an alkaline condensation reaction. The slits formed between the two-dimensional layers can accurately identify quinolone antibiotic molecules such as norfloxacin, so that the antibiotic molecules are selectively enriched on the surface of the material. At the same time, the positively charged Fe-O bonds on the surface of the Fe3O4 core and the negatively charged COF hydroxyl groups form a stable core-shell composite structure through electrostatic attraction, constructing a stable interface with quinolone antibiotic molecule recognition function. Under the synergistic mechanism of Fe3O4 and COF, quinolone antibiotic molecules such as norfloxacin can be efficiently adsorbed and degraded, improving anti-interference and stability, thereby improving detection sensitivity. The Fe3O4@COF electrochemical sensor can detect quinolone antibiotic molecules such as norfloxacin at a concentration of 1.0×10 -12 ~1.0×10 -4 mol / L has a wide linear range and the detection limit can reach 1.927×10 -13 mol / L; it can be widely used in the detection of quinolone antibiotics such as norfloxacin in milk and environmental water samples, and its sample recovery rate can reach 99.668%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0016] Figure 1 This is the reaction flow chart of Fe3O4@COF / GCE sensor for detecting norfloxacin; Figure 2a is the SEM scan of Fe3O4@COF nanoparticles; Figure 2b is the TEM scan of Fe3O4@COF nanoparticles; Figure 3a It is the detection linearity plot of cyclic voltammetry; Figure 3b is the electrochemical impedance spectroscopy; Figure 3c The concentration gradient is 10 -8 ~10 -4 Linearity plot of differential pulse voltammetry detection within the M range; Figure 3d The concentration gradient is 10 -12 ~10 -9 Detection linearity plot of differential pulse voltammetry within the M range. DETAILED DESCRIPTION

[0017] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0018] An embodiment of the present invention provides a Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising: a base electrode with a surface modified with a solid film; the solid film is a Fe3O4@COF composite material; the Fe3O4@COF composite material comprises: a core composed of ferrosoferric oxide with a porous structure and a COF shell layer attached to the surface of the core; the COF shell layer is a covalent organic framework layer formed by copolymerization of an aromatic aldehyde compound and a polyamino aromatic compound.

[0019] The Fe3O4 core provides a rich Fe 2+ / Fe 3+ Redox active sites will produce reactive oxygen species (ROS) (such as ·OH radicals) during the detection of quinolone antibiotic molecules such as norfloxacin. These free radicals have strong oxidizing properties and can efficiently oxidize and degrade quinolone antibiotic molecules. The mesoporous structure can significantly increase the specific surface area of the material, promoting the adsorption and catalytic degradation of quinolone antibiotic molecules. The oxidized and degraded molecules will generate characteristic current signals, and the oxidation products will form a conductive layer on the electrode surface, triggering cascade amplification of the electrochemical signal and increasing the electron transfer rate, thereby improving the detection sensitivity of the sensor.

[0020] The COF outer shell forms a highly ordered two-dimensional layered structure through an alkaline condensation reaction. The slit pores (0.5~2 nm) formed between the two-dimensional layers are size-selective for quinolone antibiotic molecules. The hydroxyl groups rich in its surface achieve specific adsorption of quinolone antibiotic molecules through hydrogen bonding and π-π stacking effect. This molecular sieve effect and selective adsorption capacity enable the quinolone antibiotic molecules in the detection system to be selectively enriched on the material surface, significantly increasing the local concentration, thereby improving the detection sensitivity of quinolone antibiotic molecules; at the same time, the positively charged Fe-O bonds on the surface of the Fe3O4 core and the negatively charged COF hydroxyl groups form a stable core-shell composite structure through electrostatic attraction, constructing a stable interface with quinolone antibiotic molecular recognition function, optimizing the interfacial electron transfer path, and accelerating the interfacial reaction kinetics, thereby improving the anti-interference and stability of the sensor and enhancing the detection sensitivity.

[0021] Under the synergistic mechanism of Fe3O4 and COF, quinolone antibiotic molecules such as norfloxacin can be efficiently adsorbed and degraded, improving anti-interference and stability, thereby enhancing detection sensitivity.

[0022] Specifically, the aromatic aldehyde compound is one or more of dimethoxyterephthalaldehyde (DMTP), terephthalaldehyde, benzaldehyde, salicylaldehyde, and vanillin; the polyamino aromatic compound is one or more of 1,3,5-tris(4-aminophenyl)benzene (TAPB), p-phenylenediamine, and 2,4,6-triaminopyrimidine. The molar ratio of the aromatic aldehyde compound to the polyamino aromatic compound is 1:(1-2). The mesopore diameter of the ferrosoferric oxide is 20-50 nm.

[0023] As a diamine, p-phenylenediamine contains two amino groups, which can react with the metal ions (Fe 2+ or Fe 3+ ) form coordination bonds, thereby modifying the material surface and enhancing dispersibility or stability. 1,3,5-Tris(4-aminophenyl)benzene and 2,4,6-triaminopyrimidine, as triamino monomers, contain three amino groups and a more symmetrical spatial distribution. This structure can provide more coordination sites, forming stronger coordination bonds with Fe₃O₄, and has a stronger coordination effect, resulting in a more stable surface modification. Furthermore, the three amino groups may promote more complex cross-linked structures during the synthesis process, such as forming a three-dimensional network that encapsulates Fe₃O₄ nanoparticles during polymerization.

[0024] In the surface modification of Fe3O4 nanoparticles, the number and spatial distribution of amino groups have a significant impact on the stability and functionalization of the material.

[0025] As a diamine, p-phenylenediamine has two primary amino groups that can react with Fe on the surface of Fe3O4. 2+ / Fe 3+ The ions form bidentate coordination bonds (Fe-N bonds), thereby improving the dispersibility of the nanoparticles and inhibiting their oxidation to enhance stability. Triamino monomers such as 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-triaminopyrimidine, due to their C3 symmetry and tridentate coordination configuration (bond angle 120°), can form tripodal anchoring coordination with the Fe3O4 surface, improving the stability of the modified layer. In addition, the triamino monomer can condense with three aldehyde monomers to construct a cross-linking density of 10 20 cm -3 The COF network above encapsulates Fe3O4 particles in a 20-50 nm thick shell. However, triamino monomers are prone to amorphous products during the reaction due to insufficient kinetic control.

[0026] Dimethoxyterephthalaldehyde is used as a dialdehyde monomer. The para-distributed aldehyde groups react with polyamine monomers through base condensation to form a two-dimensional lattice connected by β-ketoenamine. The interlayers form ordered slit pores (0.5~2 nm) through π-π stacking, which has a selective adsorption effect on small molecules. Dimethoxyterephthalaldehyde contains two para-distributed aldehyde groups, which easily form a two-dimensional layered COF after condensation with polyamine monomers. The narrow pores formed between the two-dimensional layers are suitable for the selective adsorption of small molecules. The +I / +M effect of the ortho-methoxy group reduces the electrophilicity of the aldehyde carbon, inhibits side reactions, improves the crystallinity of the imine bond, and suppresses the production of amorphous products by the triamino monomer. In addition, the steric hindrance and hydrolysis resistance of the methoxy group can make the material highly resistant to acids and alkalis. At the same time, the electron-donating effect of the methoxy group can regulate the band structure of the COF and optimize its photocatalytic or electrochemical properties. The two-dimensional layered structure inhibits the "shuttle effect" of polysulfides and improves the stability of the current.

[0027] The present invention provides a method for preparing a Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising the following steps: S1: Preparation of Fe3O4 nanoparticles; S2: dissolving an aromatic aldehyde compound and a polyamino aromatic compound in a solvent to form a mixed solution; adding the Fe3O4 nanoparticles to the mixed solution, and performing ultrasonic treatment under the action of a catalyst to prepare a Fe3O4@COF composite material; S3: drop-coating the Fe3O4@COF composite material on the surface of the electrode to form a solid film to obtain a finished product.

[0028] In the above step S1, the method for preparing Fe3O4 nanoparticles includes the following steps: S11: dissolving ferrous salt and aluminum salt in distilled water, adding ammonia water and mixing well to form a reaction solution, subjecting the reaction solution to an oxidation-reduction reaction at 50-60° C., and performing ultrasonic treatment to obtain a suspension; S12: Separating the magnetic precipitate phase in the suspension by magnetic separation, drying the magnetic precipitate phase, and nano-crushing the magnetic precipitate phase to obtain the Fe3O4 nanoparticles.

[0029] The solvent is a mixed solution of butanol and 1,4-dioxane in a volume ratio of (1-3):1; the catalyst can be acetic acid; the mass ratio of ferrous salt, aluminum salt, and ammonia is 2:(2-3):(1-10); and the redox reaction temperature is 50-60°C.

[0030] The base electrode was subjected to cyclic voltammetry scanning activation treatment in the potential range of -0.6 ~ 1.0 V (reference electrode) at a scan rate of 50~100 mV / s, and the number of cycles was 10~20.

[0031] The embodiment of the present invention provides an application of a Fe3O4@COF electrochemical sensor based on a covalent organic framework in the detection of norfloxacin.

[0032] Figure 1 This is the reaction flow chart of Fe3O4@COF / GCE sensor for detecting norfloxacin. Figure 1 The above-mentioned application method comprises: placing a three-electrode system of a working electrode, a counter electrode and a reference electrode in an electrolytic cell containing an electrolyte; the working electrode is the Fe3O4@COF electrochemical sensor; Configuration 10 -12 ~10 -4 M concentration gradient of norfloxacin standard solution; Differential pulse voltammetry was used to detect the oxidation peak current values of norfloxacin standard solutions with different concentration gradients. A linear regression equation was obtained by performing a linear regression between the oxidation peak current value I and the concentration C. A certain amount of sample was placed in the electrolytic cell, and the oxidation peak current value of the sample was detected by differential pulse voltammetry. The concentration of norfloxacin in the sample was calculated by the following formula (1): C=(Ib) / k(1) Specifically, the Fe3O4@COF electrochemical sensor uses a glassy carbon electrode as the base electrode, creating an Fe3O4@COF / GCE sensor. A platinum wire electrode is used as the counter electrode, and a saturated calomel electrode is used as the reference electrode. The electrolyte in the electrolytic cell consists of a PBS buffer solution with a volume ratio of (4-5):1 and a potassium ferricyanide solution with a molar concentration of 3-5 mmol / L.

[0033] The following is further described with reference to specific examples.

[0034] Example 1 An embodiment of the present invention provides a Fe3O4@COF electrochemical sensor based on a covalent organic framework, namely a Fe3O4@COF / GCE sensor. The COF outer layer is a covalent organic framework layer formed by copolymerization of dimethoxyterephthalaldehyde and 1,3,5-tris(4-aminophenyl)benzene.

[0035] The present invention provides a method for preparing a Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising the following steps: 1) Dissolve 10.0 g of ferrous sulfate and 15.0 g of aluminum chloride hexahydrate in 200 mL of double-distilled water to form solution A. Heat solution A to 50°C on a magnetic stirrer. Add 15 mL of aqueous ammonia to 100 mL of double-distilled water to form solution B. Mix solutions A and B, add 3–4 drops of ethanol, and sonicate at 150 W for 30 min to obtain suspension C. 2) The magnetic precipitate phase in the coagulated suspension C is adsorbed by a magnet, the coagulated precipitate phase is filtered and dried, and then nano-scaled using a ball mill to obtain Fe3O4 nanopowder; 3) Mix 20 mL of butanol and 20 mL of ethanol to obtain solvent D. Disperse 87 mg of dimethoxyterephthalaldehyde in solvent D and sonicate at 100 W for 10 min to obtain suspension E. Disperse 105 mg of 1,3,5-tris(4-aminophenyl)benzene in suspension E and sonicate at 100 W for 10 min to obtain suspension F. 4) Fe3O4 nanopowder was dispersed in suspension F to obtain suspension G. 0.05 mL of acetic acid was rapidly added dropwise to suspension G, and the suspension was ultrasonically treated at 150 W for 2 h to obtain suspension H. 0.45 mL of acetic acid was added to suspension H, and the suspension was refluxed at 70°C for 48 h to obtain suspension I. Suspension I was washed and freeze-dried for 24 h to obtain the Fe3O4@COF composite material.

[0036] 5) Polish a glassy carbon electrode with 0.02 μm diameter alumina powder; rinse the polished glassy carbon electrode with deionized water, ultrasonically clean it in deionized water for 3 minutes, ultrasonically clean it in anhydrous ethanol for 3 minutes, and ultrasonically clean it in deionized water for 3 minutes; place the cleaned glassy carbon electrode in 0.5 M sulfuric acid solution and activate it by cyclic voltammetry at a potential range of -0.6 to 1.0 V for 50 cycles; rinse it with deionized water after activation and place it in deionized water for later use; take 6 μL of Fe3O4@COF composite material, take it and drop it on the surface of the activated glassy carbon electrode, and store it in a refrigerator at 4-8°C for about 4 hours to form a uniform solid film, thus preparing the Fe3O4@COF / GCE sensor.

[0037] Example 2 An Fe3O4@COF electrochemical sensor based on a covalent organic framework (COF) is provided in an embodiment of the present invention. The COF outer layer is a COF layer formed by copolymerizing terephthalaldehyde and p-phenylenediamine in a 1:1 molar ratio. Its preparation method is the same as in Example 1.

[0038] Example 3 An Fe3O4@COF electrochemical sensor based on a covalent organic framework (COF) is provided in this embodiment. The COF outer layer is a COF layer formed by copolymerizing 2,4,6-triaminopyrimidine with a mixture of benzaldehyde, salicylaldehyde, and vanillin in a molar ratio of 1:2. Its preparation method is the same as in Example 1.

[0039] Example 4 The Fe3O4@COF electrochemical sensor based on a covalent organic framework and the preparation method provided in this embodiment of the present invention are the same as those in Example 1. The difference is that the mass ratio of ferrous sulfate, aluminum chloride hexahydrate and ammonia water is 1:1:5.

[0040] Example 5 The Fe3O4@COF electrochemical sensor based on a covalent organic framework and the preparation method provided in this embodiment of the present invention are the same as those in Example 1. The difference is that the mass ratio of ferrous sulfate, aluminum chloride hexahydrate and ammonia water is 2:3:1.

[0041] Example 6 The Fe3O4@COF electrochemical sensor based on a covalent organic framework and the preparation method provided in this embodiment of the present invention are the same as those in Example 1.

[0042] The Fe3O4@COF electrochemical sensor application method includes: 1) Prepare PBS buffer solution with pH=6.5; 2) Weigh a certain amount of norfloxacin and dissolve it in ultrapure water to make a volume of 10 -12 ~10 -4 M concentration gradient of norfloxacin standard solution; 3) Weigh a certain amount of potassium ferrocyanide and dissolve it in ultrapure water to prepare a 3mM potassium ferrocyanide solution; 4) Construct a three-electrode system: Pipette 5 mL of PBS buffer solution into the electrolytic cell and add 1 mL of potassium ferricyanide solution to form the electrolyte. Use a glassy carbon electrode modified with the Fe3O4@COF composite material as the working electrode, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. The operating conditions are: initial potential of -0.2 V, peak potential of 0.7 V, scan rate of 0.05 V / s, pulse width of 50 ms, and dwell time of 2 min.

[0043] 5) Take 10 -12 ~10 -4 M different concentration gradients of norfloxacin standard solution, each concentration was taken 1 μL 10 times, with a sampling interval of 0.1 s.

[0044] 6) Differential pulse voltammetry was used to detect and record the oxidation peak current values at different concentration gradients, and a linear regression was performed between the oxidation peak current value I and the concentration C to obtain the linear regression equation I=kC+b (k and b are both constants); 7) Add 10 μL of sample to the electrolytic cell three times. Detect and record the oxidation peak current values I1, I2, and I3 by differential pulse voltammetry. Calculate the corresponding concentrations C1, C2, and C3 of I1, I2, and I3 using the linear regression equation. The average value of C1, C2, and C3 is the norfloxacin concentration in the sample.

[0045] The detection of norfloxacin is further described below.

[0046] 1. Electron microscope scanning morphology analysis Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to scan the prepared Fe3O4@COF nanoparticles. Figure 2a This is the SEM scan of Fe3O4@COF nanoparticles. Figure 2b This is the TEM scanning image of Fe3O4@COF nanoparticles.

[0047] Figure 2a shows the surface morphology of Fe3O4@COF nanoparticles. It can be seen from Figure 2a that the nanoparticles are uniformly distributed spherical particles. These particles are tightly attached to the core surface, creating a relatively regular surface pattern. This uniform distribution of spherical particles not only indicates that the material has good dispersibility, but also reflects its high specific surface area.

[0048] Figure 2b The internal structure of Fe3O4@COF nanoparticles was characterized in detail, showing the shell structure of Fe3O4@COF nanoparticles. Figure 2b The nanoparticles clearly exhibit a core-shell structure, with the core composed of Fe₃O₄ magnetic nanoparticles and the shell serving as a covalent organic framework. Particularly noteworthy is the serrated structure on the shell surface. This unique shape not only increases the material's specific surface area but also provides it with more active sites, enhancing its ability to contact and react with substrates.

[0049] 2. Cyclic voltammetry and differential pulse voltammetry 2.1 Experimental subjects Experimental group: Fe3O4@COF electrochemical sensor of Example 6; Control group: glassy carbon electrode.

[0050] 2.2 Experimental methods 1) Prepare PBS buffer solution with pH=6.5; 2) Weigh a certain amount of norfloxacin and dissolve it in ultrapure water to make a volume of 10 -12 ~10 -4 M concentration gradient of norfloxacin standard solution; 3) Weigh a certain amount of potassium ferrocyanide and dissolve it in ultrapure water to prepare a 3mM potassium ferrocyanide solution; 4) Construct a three-electrode system: Pipette 5 mL of PBS buffer solution into the electrolytic cell and add 1 mL of potassium ferricyanide solution to form the electrolyte. Use the Fe3O4@COF electrochemical sensor and glassy carbon electrode as working electrodes, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. The operating conditions for cyclic voltammetry detection are as follows: a standing time of 2 min, an initial potential of -0.2 V, a peak potential of 0.7 V, a scan rate of 0.05 V / s, and a sensitivity of 10 μA / V.

[0051] 5) Take 10 -12 ~10 -4 M different concentration gradients of norfloxacin standard solution, each concentration was taken 1 μL 10 times, with a sampling interval of 0.001V.

[0052] 6) Cyclic voltammetry was used to measure and record the oxidation peak current and charge transfer resistance values of the experimental and control groups in the potential range of -0.2 to 0.7 V. Differential pulse voltammetry was also used to measure and record the oxidation peak current values of the experimental group at different concentration gradients. 2.3 Results Analysis Figure 3a is the detection linearity plot of cyclic voltammetry, Figure 3b It is an electrochemical impedance spectrum; “Fe3O4+Cof” represents Fe3O4@COF electrochemical sensor, and “Bare electrode” represents glassy carbon electrode.

[0053] Depend on Figure 3a It can be seen that the redox peak current of the electrode coated with Fe3O4@COF is significantly enhanced; Figure 3b As can be seen, the resistance of the electrode coated with Fe3O4@COF is significantly lower than that of the glassy carbon electrode. This indicates that the Fe3O4@COF electrochemical sensor of this embodiment of the present invention is more conductive than the glassy carbon electrode without Fe3O4@COF coating, and that the Fe3O4@COF composite material can enhance electron transfer efficiency.

[0054] Figure 3c The concentration gradient is 10 -8 ~10 -4 Linearity diagram of differential pulse voltammetry detection within the range of M, Figure 3d The concentration gradient is 10 -12 ~10 -9Differential pulse voltammetry detection linearity diagram within the range of M; wherein the abscissa represents the concentration index n; the ordinate represents the oxidation peak current value.

[0055] Depend on Figure 3c Can be obtained in 10 -8 ~10 -4 The mol / L oxidation peak current showed a good linear relationship with its concentration. The linear regression equation was y=-0.1759x+1.6742, and the correlation coefficient was R 2 =0.98812; by Figure 3d It can be seen that the concentration is 10 -12 ~10 -9 mol / L, the linear regression equation is y=-0.024x+0.4625, and the correlation coefficient is R 2 =0.98914, R refers to the Pearson correlation coefficient, and R < 1 indicates negative linear correlation. In the low concentration range, the minimum concentration detection limit is 1.927×10 -13 mol / L.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A Fe3O4@COF electrochemical sensor based on a covalent organic framework, characterized in that: include: A base electrode with a solid film modified on its surface; The solid film is a Fe3O4@COF composite material; the Fe3O4@COF composite material comprises: a core composed of ferroferric oxide with a porous structure and a COF shell layer attached to the surface of the core; The COF outer shell layer is a covalent organic skeleton layer formed by copolymerization of aromatic aldehyde compounds and polyamino aromatic compounds.

2. The Fe3O4@COF electrochemical sensor based on a covalent organic framework according to claim 1, characterized in that The aromatic aldehyde compound is one or more of dimethoxyterephthalaldehyde, terephthalaldehyde, benzaldehyde, salicylaldehyde and vanillin; the polyamino aromatic compound is one or more of 1,3,5-tris(4-aminophenyl)benzene, p-phenylenediamine and 2,4,6-triaminopyrimidine.

3. The Fe3O4@COF electrochemical sensor based on a covalent organic framework according to claim 1, characterized in that The molar ratio of the aromatic aldehyde compound to the polyamino aromatic compound is 1:(1-2).

4. The Fe3O4@COF electrochemical sensor based on a covalent organic framework according to claim 1, characterized in that The mesopore diameter of the ferrosoferric oxide is 20-50 nm.

5. A method for preparing a Fe3O4@COF electrochemical sensor based on a covalent organic framework according to any one of claims 1 to 4, characterized in that: include: Preparation of Fe3O4 nanoparticles; Dissolving an aromatic aldehyde compound and a polyamino aromatic compound in a solvent to form a mixed solution; adding the Fe3O4 nanoparticles to the mixed solution, and performing ultrasonic treatment under the action of a catalyst to prepare a Fe3O4@COF composite material; The Fe3O4@COF composite material is drop-coated on the surface of the electrode to form a solid film to obtain a finished product.

6. The preparation method according to claim 5, characterized in that: In the step of preparing Fe3O4 nanoparticles, the preparation method of Fe3O4 nanoparticles includes: Dissolving ferrous salt and aluminum salt in distilled water, adding ammonia water and mixing well to form a reaction solution, subjecting the reaction solution to an oxidation-reduction reaction at high temperature, and performing ultrasonic treatment to obtain a suspension; The magnetic precipitate phase in the suspension is separated by magnetic separation, and the magnetic precipitate phase is dried and nano-scale crushed to obtain the Fe3O4 nanoparticles.

7. The preparation method according to claim 6, characterized in that: The mass ratio of the ferrous salt, aluminum salt and ammonia water is 2:(2-3):(1-10); the temperature of the redox reaction is 50-60°C.

8. Use of the Fe3O4@COF electrochemical sensor based on a covalent organic framework according to any one of claims 1 to 7 in detecting norfloxacin.

9. The use according to claim 8, characterized in that The application method includes: Placing a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode in an electrolytic cell containing an electrolyte; the working electrode is the Fe3O4@COF electrochemical sensor; Configuration 10 -12 ~10 -4 M concentration gradient of norfloxacin standard solution; Differential pulse voltammetry was used to detect the oxidation peak current values of norfloxacin standard solutions with different concentration gradients. A linear regression equation was obtained by performing a linear regression between the oxidation peak current value I and the concentration C. A certain amount of sample was placed in the electrolytic cell, and the oxidation peak current value of the sample was detected by differential pulse voltammetry. The concentration of norfloxacin in the sample was calculated by the following formula (1): C=(Ib) / k(1).

10. The use according to claim 8, characterized in that The electrolyte in the electrolytic cell includes a PBS buffer solution with a volume ratio of (4-5):1 and a potassium ferricyanide solution with a molar concentration of 3-5 mmol / L.

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