Construction And Application Of Norfloxacin Molecularly Imprinted Sensor Based On CoFe-MOFs/AuNPs

Norfloxacin(NOR)is a quinolone antibiotic widely used for the treatment of human and animal diseases.However,long-term consumption of animal-derived foods containing low doses of NOR would lead to skeletal retardation,dizziness,anorexia,depression and so on.Therefore,the Ministry of Agriculture of China has pointed out to stop the operation and use of NOR for food animals.It is urgent to develop an efficient and sensitive method for the rapid detection of NOR in animal food.In this study,a MIP/Co Fe-MOFs/Au NPs/glassy carbon electrode(GCE)sensor for the detection of NOR was constructed by polypyrrole(Ppy)-based molecularly imprinted polymer(MIP),which was coated on the surface of gold nanoparticles(Au NPs)composite cobalt-iron based-metal organic frameworks(Co Fe-MOFs).After a series of characterization and process optimization of the sensor,the recognition mechanism and properties were studied.Finally,the sensor was applied to the detection of NOR in real samples.The main research contents are as follows:(1)The Au NPs prepared by reduction method were electrodeposited on the surface of GCE by cyclic voltammetry(CV),and then Co Fe-MOFs were dropped.The molecularly imprinted membrane was obtained by CV electrochemical copolymerization of pyrrole(functional monomer)and NOR(template molecule).Then MIP/Co Fe-MOFs/Au NPs/GCE was obtained by removing the template molecules by elution solution.The larger specific surface area and porosity of Co Fe-MOFs could extend the MIP membrane and increase the effective imprinted cavities,so as to overcome the shortcomings of low binding efficiency and fewer imprinted cavities of traditional MIP.Meanwhile,the high conductivity of Au NPs could make up for the poor conductivity of Co Fe-MOFs and improve the sensitivity of the sensor.Additionally,in order to avoid the potential instability of layer-by-layer assembly,I adopted sandwich-structured“MIP/Co Fe-MOFs/Au NPs”in which Co Fe-MOFs were coated with Au NPs and MIP thin membrane obtained by electropolymerization(EPm).In this way,the thickness and morphology of Au NPs and MIP membrane could be better controlled by EPm,and then the stability of the sensor could be improved.Scanning electron microscopy(SEM)characterization,CV and electrochemical impedance spectroscopy(EIS)analysis showed that the sensor was successfully constructed.Through optimization experiments,the most sensitive preparation process of MIP/Co Fe-MOFs/Au NPs/GCE sensor was obtained.(2)The recognition of MIP prepared by precipitation polymerization(PPm)is superimposed by the catalytic action of modified materials and the recognition of imprinted cavities.While the MIP membrane prepared by EPm covered the modified material,the target molecule could only be identified by the imprinted cavities embedded on the surface of the MIP.In this paper,MIP/Co Fe-MOFs/Au NPs/GCE sensor was prepared by EPm and its imprinted reaction to NOR was studied.Unlike the catalytic reaction,which depends on the electroactivity of the modified material,the imprinted reaction depends on the recognition of the target at the imprinted cavities.Therefore,the direct method,which takes NOR(target substance)as the model,is adopted from the theoretical level of the irreversible electrochemical reaction.The recognition of NOR by MIP/Co Fe-MOFs/Au NPs/GCE sensor prepared by EPm and the recognition mechanism followed in the electrochemical condition were investigated.Then the possible electrochemical reaction was deduced from the perspective of electron transfer.The kinetic process of the modified electrode in the surface imprinted reaction was described.The main kinetic parameters A and D₀ were calculated based on the application of Randles-Sevcik equation in irreversible reactions.The results showed that the recognition of NOR by the sensor was an irreversible anodic oxidation reaction involving one electron and one proton,followed the adsorption-diffusion mixing mechanism.The effective surface area of the MIP sensor modified with Co Fe-MOFs/Au NPs was 2.2 times that of the MIP sensor without modification.Therefore,Co Fe-MOFs/Au NPs could extend the MIP membrane and increase the imprinted cavities.(3)The indirect method with potassium ferricyanide as the model object was complied,the electrical conductivity of MIP/Co Fe-MOFs/Au NPs/GCE sensor was indirectly reflected by the redox reaction between Fe²⁺and Fe³⁺.Therefore,?i was used as the index to measure the current value of the sensor before and after NOR recognition.The performance of MIP/Co Fe-MOFs/Au NPs/GCE sensor prepared under the optimal process conditions was evaluated and the actual sample was tested.The results showed that the MIP/Co Fe-MOFs/Au NPs/GCE sensor has good selectivity,stability and reproducibility.The MIP sensor had a limit of detection of 0.131 pmol L^-1(S/N=3)with a wider linear concentration of 5?6000 pmol L^-1.The detection results of real samples were similar by MIP/Co Fe-MOFs/Au NPs/GCE sensor and enzyme-linked immunosorbent assay(ELISA)kit,and it was feasible and accurate to use MIP/Co Fe-MOFs/Au NPs/GCE sensor to detect actual samples.