A covalent organic framework-based Fe3O4@COF electrochemical sensor, a preparation method and applications thereof

Abstract

The embodiment of the present application provides a Fe3O4@COF electrochemical sensor based on a covalent organic framework, a preparation method and application, the electrochemical sensor comprises: a base electrode which is surface-modified with a solid film; the solid film is a Fe3O4@COF composite material; the Fe3O4@COF composite material comprises: a core formed by a porous structure of Fe3O4 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 aromatic aldehyde compounds and polyamino aromatic compounds. The Fe3O4@COF electrochemical sensor based on the covalent organic framework, the preparation method and the application can detect quinolone antibiotic molecules such as norfloxacin, and the detection limit can reach 1.927*10 ‑ 13 mol / L; and can be widely applied to the detection of quinolone antibiotics such as norfloxacin in milk and environmental water samples.

Description

Technical Field

[0001] This invention relates to the field of electrochemical sensing and detection technology, and in particular to a covalent organic framework porous Fe3O4 electrochemical sensor for detecting norfloxacin and its preparation method. Background Technology

[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 the aquatic environment can lead to microbial imbalances and even induce the development of drug-resistant genes. Furthermore, they can accumulate in the human body through the food chain, inducing the development of drug-resistant genes. Their mechanism of action is to inhibit bacterial DNA gyrase, thereby inhibiting DNA replication and transcription, leading to bacterial death. Drug-resistant bacteria may also contain resistance plasmids, which can transfer between different 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 immunosorbent assay (ELISA), and liquid chromatography (LC). Raman scattering confirms the presence of norfloxacin by comparing it to standard spectra and can quantitatively detect residues above 1 mg / kg, but its sensitivity is insufficient, with a limit of detection (LOD) only reaching the ppm level. ELISA involves immobilizing a norfloxacin-carrier protein conjugate on the surface of a microplate and measuring the absorbance (OD value) using an ELISA reader. The concentration of norfloxacin is calculated using a standard curve, allowing for quantitative detection of residues from 1 to 10 mg / kg. However, because norfloxacin has a structure similar to other quinolone antibiotics (such as ciprofloxacin and ofloxacin), it is extremely prone to antibody cross-reactions, leading to false positives or false negatives. LC detects norfloxacin's presence through its ultraviolet absorption (maximum absorption wavelength approximately 278 nm), but LC instruments and maintenance are expensive, 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] To address the technical problems existing in the prior art, and to solve the problems of low sensitivity, low accuracy, high cost and complicated operation of the existing detection methods for norfloxacin, this paper provides an Fe3O4@COF electrochemical sensor based on a covalent organic framework, its preparation method and application.

[0005] In a first aspect, the present invention provides an Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising: a base electrode with a solid film modified on its surface; the solid film being an Fe3O4@COF composite material; the Fe3O4@COF composite material comprising: a core composed of porous iron(III) oxide and a COF shell layer attached to the surface of the core; the COF shell layer being a covalent organic framework layer formed by copolymerization of aromatic aldehydes and polyamino aromatic compounds.

[0006] Preferably, the aromatic aldehyde compound is one or more of dimethoxytetraphenylaldehyde, 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 size of the iron oxide is 20~50 nm.

[0009] Secondly, the present invention also provides a method for preparing a Fe3O4@COF electrochemical sensor based on a covalent organic framework as described above, comprising the following steps:

[0010] Preparation of Fe3O4 nanoparticles;

[0011] Aromatic aldehydes and polyamino aromatic compounds are dissolved in a solvent to form a mixture; Fe3O4 nanoparticles are added to the mixture and ultrasonically treated under the action of a catalyst to obtain Fe3O4@COF composite material;

[0012] The finished product is obtained by drop-coating the Fe3O4@COF composite material onto the surface of the electrode to form a solid film.

[0013] Preferably, in the step of preparing Fe3O4 nanoparticles, the method for preparing Fe3O4 nanoparticles includes:

[0014] Ferrous salt and aluminum salt are dissolved in distilled water, and ammonia water is added and mixed to form a reaction solution. The reaction solution is subjected to a redox reaction at high temperature and then ultrasonically treated to obtain a suspension.

[0015] The Fe3O4 nanoparticles are obtained by separating the magnetic aggregate phase in the suspension by magnetic separation, and then drying and nano-scale pulverization of the magnetic aggregate phase.

[0016] Preferably, the mass ratio of the ferrous salt, aluminum salt and ammonia is 2:(2~3):(1~10); the temperature of the redox reaction is 50~60℃.

[0017] Thirdly, the present invention also provides an application of the Fe3O4@COF electrochemical sensor based on the covalent organic framework as described above in the detection of norfloxacin.

[0018] Preferably, 9. The application according to claim 8, wherein the application method comprises:

[0019] A three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode is placed in an electrolytic cell containing an electrolyte; the working electrode is the Fe3O4@COF electrochemical sensor.

[0020] Configuration 10 -12 ~10 -4 Norfloxacin standard solutions with M concentration gradient;

[0021] The oxidation peak current values ​​of norfloxacin standard solutions with different concentration gradients were detected by differential pulse voltammetry. The oxidation peak current value I was linearly regressed with the concentration C to obtain the linear regression equation I=kC+b.

[0022] A certain amount of sample was placed in an 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):

[0023] C=(Ib) / k(1)

[0024] 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.

[0025] The beneficial effects of this invention are as follows:

[0026] The Fe3O4@COF electrochemical sensor provided by this invention is an electrode formed by modifying the surface of a base electrode with a solid film of Fe3O4@COF composite material. This Fe3O4@COF composite material has a core of highly catalytically active and porous iron(III) oxide, and an outer shell composed of a covalent organic framework formed by the covalent condensation reaction of aromatic aldehydes and polyamino aromatic compounds. The Fe3O4 core provides abundant Fe... 2+ / Fe 3+The redox active sites generate reactive oxygen species (ROS) during detection, which can efficiently oxidize and degrade quinolone antibiotic molecules such as norfloxacin. The COF shell layer forms a highly ordered two-dimensional layered structure through an alkaline condensation reaction. The narrow pores formed between the two-dimensional layers can accurately identify quinolone antibiotic molecules such as norfloxacin, allowing for selective enrichment of antibiotic molecules on the material surface. Simultaneously, the positively charged Fe-O bonds on the Fe3O4 core surface 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 enhancing detection sensitivity. This Fe3O4@COF electrochemical sensor can detect quinolone antibiotic molecules such as norfloxacin within 1.0 × 10⁻⁶. -12 ~1.0×10 -4 It exhibits a wide linear range at mol / L, with a detection limit reaching 1.927 × 10⁻⁶. -13 It has a concentration of mol / L and can be widely used to detect quinolone antibiotics such as norfloxacin in milk and environmental water samples, with a sample recovery rate of up to 99.668%. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0028] Figure 1 This is a flow chart of the reaction process for detecting norfloxacin using the Fe3O4@COF / GCE sensor;

[0029] Figure 2a This is a SEM scan of Fe3O4@COF nanoparticles;

[0030] Figure 2b This is a TEM scan of Fe3O4@COF nanoparticles;

[0031] Figure 3a This is the detection linearity graph of cyclic voltammetry;

[0032] Figure 3b It is an electrochemical impedance spectroscopy (EIS) spectrum.

[0033] Figure 3c The concentration gradient is at 10 -8 ~10 -4 Linearity graph detected by differential pulse voltammetry within the M range;

[0034] Figure 3d The concentration gradient is at 10 -12 ~10 -9The linear graph of the detection was obtained by differential pulse voltammetry within the M range. Detailed Implementation

[0035] To make the objectives, 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 only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort 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.

[0036] This invention provides an Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising: a base electrode with a solid film modified on its surface; the solid film being a Fe3O4@COF composite material; the Fe3O4@COF composite material comprising: a core composed of porous iron(III) oxide and a COF shell layer attached to the surface of the core; the COF shell layer being a covalent organic framework layer formed by copolymerization of aromatic aldehydes and polyamino aromatic compounds.

[0037] The Fe3O4 core provides abundant Fe... 2+ / Fe 3+ Redox active sites generate reactive oxygen species (ROS, such as ·OH radicals) during the detection of quinolone antibiotic molecules like norfloxacin. These radicals are highly oxidizing and can efficiently oxidize and degrade quinolone antibiotic molecules. Their 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 generate characteristic current signals, and the oxidation products form a conductive layer on the electrode surface, triggering a cascade amplification of the electrochemical signal, increasing the electron transfer rate, and thus improving the detection sensitivity of the sensor.

[0038] 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 exhibit size selectivity for quinolone antibiotic molecules. The hydroxyl groups on its surface achieve specific adsorption of quinolone antibiotic molecules through hydrogen bonding and π-π stacking effects. This molecular sieve effect and selective adsorption capability selectively enrich quinolone antibiotic molecules on the material surface, significantly increasing the local concentration and thus improving the detection sensitivity of quinolone antibiotic molecules. At the same time, the positively charged Fe-O bonds on the Fe3O4 core surface 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. This optimizes the interface electron transport path, accelerates the interface reaction kinetics, and thus improves the sensor's anti-interference and stability, and enhances the detection sensitivity.

[0039] Under the synergistic mechanism of Fe3O4 and COF, it can efficiently adsorb and degrade quinolone antibiotic molecules such as norfloxacin, improve anti-interference and stability, and thus enhance detection sensitivity.

[0040] Specifically, the aromatic aldehyde compound is one or more selected from dimethoxyterephthalaldehyde (DMTP), terephthalaldehyde, benzaldehyde, salicylaldehyde, and vanillin; the polyamino aromatic compound is one or more selected from 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 mesoporous pore size of the iron(III) oxide is 20~50 nm.

[0041] p-Phenylenediamine, as a diamine, contains two amino groups and can react with metal ions (Fe3O4) on the surface of Fe3O4. 2+ or Fe 3+ These amino groups form coordination bonds, thereby modifying the material surface and enhancing its dispersibility or stability. 1,3,5-Tris(4-aminophenyl)benzene and 2,4,6-triaminopyrimidine, as triamino monomers, contain three amino groups with a more symmetrical spatial distribution. This structure provides more coordination sites, forming stronger coordination bonds with Fe3O4, resulting in more stable surface modification. Furthermore, the three amino groups may promote more complex cross-linking structures during synthesis, such as forming a three-dimensional network during polymerization to encapsulate Fe3O4 nanoparticles.

[0042] 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.

[0043] p-Phenylenediamine, as a diamine, has two primary amino groups that can react with Fe on the surface of Fe3O4. 2+ / Fe3+ Ions form bidentate coordination bonds (Fe-N bonds), thereby improving the dispersibility of nanoparticles and inhibiting their oxidation-enhanced stability. Triamino monomers such as 1,3,5-tris(4-aminophenyl)benzene and 2,4,6-triaminopyrimidine, due to their C3 symmetry and bidentate coordination configuration (bond angle 120°), can form tripole-anchored coordination with the Fe3O4 surface, improving the stability of the modified layer. In addition, triamino monomers can condense with three aldehyde monomers to construct crosslinking densities reaching 10. 20 cm -3 The COF network described above encapsulates Fe3O4 particles in a shell 20–50 nm thick. However, the triamino monomer is highly susceptible to amorphous products due to insufficient kinetic control during the reaction.

[0044] Dimethoxy-terephthalaldehyde, as a dialdehyde monomer, forms a two-dimensional lattice with β-keto-enamine linkages through a base condensation reaction between the para-distributed aldehyde groups and polyamine monomers. Ordered slit pores (0.5–2 nm) are formed between the layers via π-π stacking, exhibiting selective adsorption effects for small molecules.

[0045] Dimethoxy-terephthalaldehyde contains two para-positioned aldehyde groups, which readily form a two-dimensional layered COF upon condensation with polyamine monomers. The narrow pores formed between the two 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, increases the crystallinity of the imine bond, and suppresses the formation of amorphous products from the triamine monomer. Furthermore, the steric hindrance and hydrolysis resistance of the methoxy group enable the material to exhibit strong acid and alkali resistance. Simultaneously, the electron-donating effect of the methoxy group can modulate the band structure of the COF, optimizing its photocatalytic or electrochemical performance. The two-dimensional layered structure suppresses the "shuttle effect" of polysulfides, improving current stability.

[0046] This invention provides a method for preparing a Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising the following steps:

[0047] S1: Preparation of Fe3O4 nanoparticles;

[0048] S2: Aromatic aldehydes and polyamino aromatic compounds are dissolved in a solvent to form a mixture; Fe3O4 nanoparticles are added to the mixture and ultrasonically treated under the action of a catalyst to obtain Fe3O4@COF composite material;

[0049] S3: The Fe3O4@COF composite material is drop-coated onto the surface of the electrode to form a solid film, thus obtaining the finished product.

[0050] In step S1 above, the preparation method of Fe3O4 nanoparticles includes the following steps:

[0051] S11: Dissolve ferrous salt and aluminum salt in distilled water, add ammonia water and mix well to form a reaction solution. The reaction solution undergoes a redox reaction at 50~60℃ and is then subjected to ultrasonic treatment to obtain a suspension.

[0052] S12: The magnetic aggregate phase in the suspension is separated by magnetic separation, and the magnetic aggregate phase is dried and nano-sized pulverized to obtain the Fe3O4 nanoparticles.

[0053] 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); the temperature of the redox reaction is 50~60℃.

[0054] The base electrode was activated by cyclic voltammetry at a scan rate of 50 to 100 mV / s within a potential range of -0.6 to 1.0 V (reference electrode), with 10 to 20 cycles.

[0055] This invention provides an application of a covalent organic framework-based Fe3O4@COF electrochemical sensor in the detection of norfloxacin.

[0056] Figure 1 This is a reaction flow diagram for the detection of norfloxacin using a Fe3O4@COF / GCE sensor. (Reference) Figure 1 The above-mentioned application method includes: placing a three-electrode system of a working electrode, a counter electrode, and a reference electrode in an electrolytic cell containing an electrolyte; wherein the working electrode is the Fe3O4@COF electrochemical sensor;

[0057] Configuration 10 -12 ~10 -4 Norfloxacin standard solutions with M concentration gradient;

[0058] The oxidation peak current values ​​of norfloxacin standard solutions with different concentration gradients were detected by differential pulse voltammetry. The oxidation peak current value I was linearly regressed with the concentration C to obtain the linear regression equation I=kC+b.

[0059] A certain amount of sample was placed in an 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):

[0060] C=(Ib) / k(1)

[0061] Specifically, the Fe3O4@COF electrochemical sensor uses a glassy carbon electrode as the base electrode, constructing a 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 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.

[0062] The following specific examples will provide further explanation.

[0063] Example 1

[0064] The Fe3O4@COF electrochemical sensor based on a covalent organic framework provided in this embodiment of the invention is a Fe3O4@COF / GCE sensor. The COF shell layer is a covalent organic framework layer formed by the copolymerization of dimethoxytetraphenyl phthalaldehyde and 1,3,5-tris(4-aminophenyl)benzene.

[0065] This invention provides a method for preparing a Fe3O4@COF electrochemical sensor based on a covalent organic framework, comprising the following steps:

[0066] 1) Dissolve 10.0g of ferrous sulfate and 15.0g of aluminum chloride hexahydrate in 200mL of double-distilled water to form solution A; place solution A on a magnetic stirrer and heat to 50℃, add 15mL of ammonia water to 100mL of double-distilled water to form solution B; mix solution A and solution B, add 3-4 drops of ethanol, and sonicate at 150W for 30min to obtain suspension C;

[0067] 2) The magnetic precipitate phase in the coagulated suspension C is adsorbed by a magnet. The precipitate phase after coagulation is filtered and dried, and then pulverized into Fe3O4 nanopowder by ball milling.

[0068] 3) Mix 20 mL of butanol and 20 mL of sodium hydroxide to obtain solvent D. Disperse 87 mg of dimethoxytetraphenyl phthalaldehyde 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.

[0069] 4) Disperse Fe3O4 nanopowder in suspension F to obtain suspension G. Add 0.05 mL of acetic acid dropwise to suspension G and sonicate at 150 W for 2 h to obtain suspension H. Add 0.45 mL of acetic acid to suspension H and reflux at 70 °C for 48 h to obtain suspension I. Wash suspension I and freeze-dry for 24 h to obtain Fe3O4@COF composite material.

[0070] 5) Polish the glassy carbon electrode with 0.02 μm diameter alumina powder; then rinse the polished glassy carbon electrode with deionized water, place it in deionized water for ultrasonic cleaning for 3 min, then place it in anhydrous ethanol for ultrasonic cleaning for 3 min, and then place it in deionized water for ultrasonic cleaning for 3 min; place the cleaned glassy carbon electrode in 0.5 M sulfuric acid solution and activate the electrode by cyclic voltammetry in a potential range of -0.6 to 1.0 V for 50 cycles; after activation, rinse it with deionized water and place it in deionized water for later use; take 6 μL of Fe3O4@COF composite material, drop it onto the surface of the activated glassy carbon electrode, and place it in a refrigerator at 4~8℃ for about 4 h to form a uniform solid film, thus obtaining the Fe3O4@COF / GCE sensor.

[0071] Example 2

[0072] The Fe3O4@COF electrochemical sensor based on a covalent organic framework provided in this embodiment of the invention is a Fe3O4@COF / GCE sensor. The COF shell layer is a covalent organic framework layer formed by copolymerization of terephthalaldehyde and p-phenylenediamine in a molar ratio of 1:1. Its preparation method is the same as in Example 1.

[0073] Example 3

[0074] The Fe3O4@COF electrochemical sensor based on a covalent organic framework provided in this embodiment of the invention is a Fe3O4@COF / GCE sensor. The COF shell layer is a covalent organic framework layer formed by copolymerizing a mixture of benzaldehyde, salicylaldehyde, and vanillin in a molar ratio of 1:2 with 2,4,6-triaminopyrimidine. Its preparation method is the same as in Example 1.

[0075] Example 4

[0076] The Fe3O4@COF electrochemical sensor based on a covalent organic framework and its preparation method provided in this embodiment of the invention are the same as in Example 1. The difference is that the mass ratio of ferrous sulfate, aluminum chloride hexahydrate, and ammonia is 1:1:5.

[0077] Example 5

[0078] The Fe3O4@COF electrochemical sensor based on a covalent organic framework and its preparation method provided in this embodiment of the invention are the same as in Example 1. The difference is that the mass ratio of ferrous sulfate, aluminum chloride hexahydrate, and ammonia is 2:3:1.

[0079] Example 6

[0080] The Fe3O4@COF electrochemical sensor based on a covalent organic framework and its preparation method provided in this embodiment of the invention are the same as in Example 1.

[0081] The application methods of this Fe3O4@COF electrochemical sensor include:

[0082] 1) Prepare a PBS buffer solution with pH=6.5;

[0083] 2) Weigh a certain amount of norfloxacin and dissolve it in ultrapure water, then dilute to a final volume of 10. -12 ~10 -4 Norfloxacin standard solutions with M concentration gradient;

[0084] 3) Weigh a certain amount of potassium ferricyanide and dissolve it in ultrapure water, then make up to a final volume to prepare a 3mM potassium ferricyanide solution;

[0085] 4) Constructing a three-electrode system: Transfer 5 mL of PBS buffer solution to the electrolytic cell and add 1 mL of potassium ferricyanide solution to form the electrolyte; use a glassy carbon electrode modified with 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; set the working conditions as follows: 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 resting time of 2 min.

[0086] 5) Take 10 -12 ~10 -4 M Norfloxacin standard solutions of different concentration gradients were sampled 1 μL 10 times for each concentration, with a sampling interval of 0.1 s.

[0087] 6) The oxidation peak current value under different concentration gradients was detected and recorded by differential pulse voltammetry. The oxidation peak current value I was linearly regressed with the concentration C to obtain the linear regression equation I=kC+b (k and b are constants).

[0088] 7) Add 10 μL of sample to the electrolytic cell in three portions. Detect and record the oxidation peak current values ​​I1, I2, and I3 using differential pulse voltammetry. Calculate the concentrations C1, C2, and C3 corresponding to I1, I2, and I3 using a linear regression equation. The average value of C1, C2, and C3 is the concentration of norfloxacin in the sample.

[0089] The following provides further explanation of the testing process for norfloxacin.

[0090] 1. Electron microscopy morphology analysis

[0091] The prepared Fe3O4@COF nanoparticles were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 2a This is a SEM scan of Fe3O4@COF nanoparticles. Figure 2b This is a TEM scan of Fe3O4@COF nanoparticles.

[0092] Figure 2a shows the surface morphology of Fe3O4@COF nanoparticles. As can be seen from Figure 2a, 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 exhibits good dispersibility, but also reflects its high specific surface area.

[0093] Figure 2b Detailed characterization of the internal structure of Fe3O4@COF nanoparticles was performed, revealing the outer shell structure of the Fe3O4@COF nanoparticles. Figure 2b As can be clearly seen, a distinct core-shell layered structure is visible within the nanoparticles. The core is composed of Fe3O4 magnetic nanoparticles, while the shell is a covalent organic framework. Of particular note 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 movable positions, enhancing its ability to contact and react with substrates.

[0094] 2. Cyclic voltammetry and differential pulse voltammetry detection

[0095] 2.1 Experimental Subjects

[0096] Experimental group: Fe3O4@COF electrochemical sensor of Example 6;

[0097] Control group: glassy carbon electrode.

[0098] 2.2 Experimental Methods

[0099] 1) Prepare a PBS buffer solution with pH=6.5;

[0100] 2) Weigh a certain amount of norfloxacin and dissolve it in ultrapure water, then dilute to a final volume of 10. -12 ~10 -4 Norfloxacin standard solutions with M concentration gradient;

[0101] 3) Weigh a certain amount of potassium ferricyanide and dissolve it in ultrapure water, then make up to a final volume to prepare a 3mM potassium ferricyanide solution;

[0102] 4) Constructing a three-electrode system: Transfer 5 mL of PBS buffer solution to the electrolytic cell and add 1 mL of potassium ferricyanide solution to form the electrolyte; use Fe3O4@COF electrochemical sensor and glassy carbon electrode as working electrodes, platinum wire electrode as counter electrode, and saturated calomel electrode as reference electrode; set the working conditions as follows: 2 min for cyclic voltammetry detection, initial potential of -0.2 V, peak potential of 0.7 V, scan rate of 0.05 V / s, and sensitivity of 10 μA / V.

[0103] 5) Take 10 -12~10 -4 M Norfloxacin standard solutions of different concentration gradients were sampled 1 μL 10 times for each concentration, with a sampling interval of 0.001V.

[0104] 6) The oxidation peak current and charge transfer resistance values ​​of the experimental group and the control group in the potential range of -0.2~0.7V were detected and recorded by cyclic voltammetry; and the oxidation peak current values ​​of the experimental group under different concentration gradients were detected and recorded by differential pulse voltammetry.

[0105] 2.3 Results Analysis

[0106] Figure 3a This is the detection linearity graph of cyclic voltammetry. Figure 3b It is an electrochemical impedance spectroscopy; where "Fe3O4+Cof" represents the Fe3O4@COF electrochemical sensor, and "Bare electrode" represents the glassy carbon electrode.

[0107] Depend on Figure 3a It can be seen that the redox peak current of the electrode coated with Fe3O4@COF is significantly enhanced; from Figure 3b It can be seen that the resistance of the electrode coated with Fe3O4@COF is significantly lower than that of the glassy carbon electrode. Therefore, the Fe3O4@COF electrochemical sensor of this embodiment exhibits stronger conductivity than the glassy carbon electrode without Fe3O4@COF coating, and the Fe3O4@COF composite material can enhance electron transfer efficiency.

[0108] Figure 3c The concentration gradient is at 10 -8 ~10 -4 Linearity plot detected by differential pulse voltammetry within the M range Figure 3d The concentration gradient is at 10 -12 ~10 -9 The linear graph of differential pulse voltammetry detection within the M range; where the horizontal axis represents the concentration index n; and the vertical axis represents the oxidation peak current value.

[0109] Depend on Figure 3c It can be obtained in 10 -8 ~10 -4 The peak current of oxidation at mol / L showed a good linear relationship with its concentration, with a linear regression equation of y = -0.1759x + 1.6742 and a correlation coefficient of R0. 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, where R refers to the Pearson correlation coefficient, and R < 1 indicates a negative linear correlation. In the low concentration range, the limit of detection is 1.927 × 10⁻⁶. -13 mol / L.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these 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. An application of a covalent organic framework-based Fe3O4@COF electrochemical sensor in the detection of norfloxacin, characterized in that, The Fe3O4@COF electrochemical sensor based on a covalent organic framework includes: 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 includes: a core composed of porous iron(III) oxide 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 aromatic aldehydes and polyamino aromatic compounds.

2. The application according to claim 1, characterized in that, The application methods include: A three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode is placed in an electrolytic cell containing an electrolyte; the working electrode is the Fe3O4@COF electrochemical sensor. Prepare norfloxacin standard solutions with different concentration gradients; The redox peak current values ​​of norfloxacin standard solutions with different concentration gradients were detected by differential pulse voltammetry. The redox peak current value I was linearly regressed with the concentration C to obtain the linear regression equation I=kC+b. A certain amount of sample was placed in an electrolytic cell, and the redox 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) 3. The application according to claim 2, 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.

4. The application according to claim 1, characterized in that, The aromatic aldehyde compound is one or more of dimethoxytetraphenylaldehyde, 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.

5. The application according to claim 1, characterized in that, The molar ratio of the aromatic aldehyde compound to the polyamino aromatic compound is 1:(1~2).

6. The application according to claim 1, characterized in that, The mesopore size of the iron oxide is 20~50 nm.

7. The application according to claim 1, characterized in that, The preparation method of the Fe3O4@COF electrochemical sensor based on a covalent organic framework includes: Preparation of Fe3O4 nanoparticles; Aromatic aldehydes and polyamino aromatic compounds are dissolved in a solvent to form a mixture; Fe3O4 nanoparticles are added to the mixture and ultrasonically treated under the action of a catalyst to obtain Fe3O4@COF composite material; The finished product is obtained by drop-coating the Fe3O4@COF composite material onto the surface of the electrode to form a solid film.

8. The application according to claim 7, characterized in that, The step of preparing Fe3O4 nanoparticles includes the following methods: Ferrous salt and aluminum salt are dissolved in distilled water, and ammonia water is added and mixed to form a reaction solution. The reaction solution is subjected to a redox reaction at high temperature and then ultrasonically treated to obtain a suspension. The Fe3O4 nanoparticles are obtained by separating the magnetic aggregate phase in the suspension by magnetic separation, and then drying and nano-scale pulverization of the magnetic aggregate phase.

9. The application according to claim 8, characterized in that, The mass ratio of the ferrous salt, aluminum salt and ammonia is 2:(2~3):(1~10); the temperature of the redox reaction is 50~60℃.

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