Construction And Application Of Norfloxacin Sensor With Mixed Recognition Sites Of Peptide And Molecular Imprinting

Norfloxacin（NOR）is a third-generation quinolone antibiotic widely used to treat urinary,respiratory and gastrointestinal infections in humans and animals.However,the abuse of NOR can lead to incomplete metabolism in human and animal bodies,and excessive intake of NOR residues can cause dizziness,anorexia,lethargy and other symptoms.Therefore,it is necessary to develop a sensitive and rapid detection method for the trace detection of norfloxacin.In this paper,an electrochemical molecular-imprinted sensor for norfloxacin trace detection was constructed using BSA-Au NPs/Fe₃O₄@ZIF-8 as the base material.The modification materials and preparation process of the sensor were characterized,and the preparation parameters of the sensor were optimized.In addition,the recognition mechanism and properties of norfloxacin sensor were studied,and the detection effect of norfloxacin in milk and environmental water samples was explored.The main research contents are as follows:（1）Construction,characterization and optimization of MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor:after large surface area Fe₃O₄@ZIF-8 drops were coated on the surface of a glassy carbon electrode with an embedded magnet,BSA was loaded onto the modified electrode via Au-S bond and electrodeposited Au NPs.Finally,the molecularly imprinted membranes were polymerized by cyclic voltammetry（CV）using pyrrole as functional monomer and NOR as template molecule.After elution,the MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor was obtained.The embedding of magnets inside the electrode enables Fe₃O₄@ZIF-8 to be evenly and firmly distributed on the electrode surface,and the extremely high surface area of Fe₃O₄@ZIF-8 can provide a large number of imprinting sites for the sensor.The introduction of BSA makes the sensor with a mixed recognition site of molecular imprinting and polypeptide overcome the relatively single defect of the sensor imprinting site.The successful preparation of the sensor was verified by physical characterization and electrochemical characterization,and then the construction parameters of the sensor were optimized to achieve the best detection performance.（2）Identification response of MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor to norfloxacin:recognition of target analytes by molecularly imprinted electrochemical sensors formed by electropolymerization depends on the number of imprinted sites.Therefore,this paper directly takes the target analyte as the research model to study the sensor’s recognition reaction to the target analyte.Through the electrochemical response signal of MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor in norfloxacin solution,to explore the mechanism of norfloxacin recognition by MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor formed by electropolymerization.Subsequently,Laviorn’s law and Nernst equation were used to calculate the number of electrons and protons transferred during the recognition reaction,and then the oxidation process of norfloxacin on the surface of MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor was deduced.In addition,the effective surface areas of MIP/Fe₃O₄@ZIF-8/GCE（without magnet）,MIP/Fe₃O₄@ZIF-8/GCE（with magnet）and MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE are 0.05875 cm²,0.06786 cm² and 0.08433 cm²,respectively.Indicating that the insertion of magnets inside the electrode and the successful introduction of BSA-Au NPs greatly increased the effective recognition area of the sensor for norfloxacin,thus providing data support for the extremely high sensitivity of the sensor.（3）Performance measurement of MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor and its application in practical sample detection:the MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor prepared under optimal parameters was placed in[Fe（CN）₆]^3-4-solution for DPV scanning.TheΔi before and after adsorption was used as a reference index to study the sensor performance.The results of actual samples detected by the sensor and ELISA were compared.The results show that the MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor shows excellent selectivity,reproducibility and stability are within the acceptable range,and the linear range and detection limit of the sensor are better than those of norfloxacin sensors reported in other literature.In addition,the detection results of the sensor and ELISA kit in milk and ambient water samples were similar,indicating that MIP/BSA-Au NPs/Fe₃O₄@ZIF-8/GCE sensor is feasible for the detection of norfloxacin in ambient water and milk samples.