Construction Of Electrochemical Sensor Based On Molecular Imprinting Technique And Its Application In Food Detection

Molecularly imprinted polymers with special recognition sites and great selectivity into the target templates have become the center of attention in the fields of biomedical and food analysis in recent years.In the presence of cross-linking agents,initiators and porogens,the target molecule as template and functional monomer could form prepolymer complex through reversible covalent or non-covalent interactions.After removing the template molecule,nano-sized imprinting cavities matching the shape and function of the template molecule are left,which are able to specifically recognize target molecules.Molecularly imprinted polymers which enjoy the properties of high specificity,good chemical stability and durability have been the most promising identification elements in the field of electrochemical sensors,and are widely used to improve the selectivity of electrochemical analysis methods.The traditional methods for molecularly imprinted polymer preparation have long and complicated processes.The obtained polymer particles are irregular in shape and size,and some recognition sites in the grinding process are destroyed,which cause increasing production cost.In addition,the poor conductivity of molecularly imprinted polymers greatly limits the further development of molecularly imprinted electrochemical sensors.Based on the above-mentioned problems,this paper adopts electropolymerization method to prepare molecularly imprinted polymers on the surface of glassy carbon electrodes.This process is economical and simple.The thickness and density of molecularly imprinted polymer films can be controlled by optimizing electropolymerization conditions.Not only is it conducive to the subsequent elution of template molecules,it can also increase the number of effective recognition sites and improve the recognition ability of the sensor.On the other hand,a series of new nano-modified materials,including metal-organic frameworks and molybdenum carbide,have been developed to increase the effective active area on the electrode surface,improve the electron transfer rate,amplify the electrochemical signal,and thereby improve the sensitivity of the sensor.The specific work is as follows:1.A simple solvothermal method was used to synthesize MIL-53?Fe?,a kind of iron-based metal organic frameworks with regular cubic structure which provides a large specific surface area for the subsequent loading of molecularly imprinted polymers.MIL-53?Fe?also contains abundant Fe²⁺/Fe³⁺electron pairs,which can effectively improve the electron transfer rate,amplify the electrochemical signal and build an efficient and sensitive sensing platform.The template molecule melamine was combined with the functional monomer methacrylic acid through hydrogen bonding.And the template molecules were removed through mechanically stirring in the elution solution composed of methanol,acetonitrile and acetic acid?v/v=3:2:2?.Under the optimal experimental conditions,the analytical performance of the sensor has been greatly improved.The detection range is from 10^-11M to 10^-6M and the detection limit is as low as 8.21×10^-12M.Compared with other reported melamine analysis methods,the results of this work are satisfactory.The actual analysis capability of this sensor in milk samples was evaluated by the standard addition method with resulted recovery rates ranging from93.4%to 103.5%,proving that this sensor provides a new and effective method for detecting the content of melamine in milk products quickly and sensitively.2.A sensitive imprinting platform was constructed by introducing nitrogen-doped molybdenum carbide?N-Mo₂C?with good conductivity.The molecularly imprinted polymer film was prepared through a simple electropolymerization method using resveratrol as the template molecule and o-phenylenediamine as the functional monomer.And then the template molecules were removed by CV scanning in Na OH solution.The prepared molecularly imprinted electrochemical sensor can realize trace analysis of resveratrol in grape seed extract samples.The experimental conditions such as the molar ratio of template molecules to functional monomers,the p H value of the polymerization solution,polymerization cycles,polymerization rate,elution cycles and adsorption time were optimized.The sensor showed great analytical performance in the concentration range of 10^-9M to 10^-4M and the detection limit was as low as 4.37×10^-10M.The recovery rates of 94.1%?110.5%were obtained by applying the sensor to the actual sample analysis.The method also has the advantages of good selectivity,reproducibility and stability,which opens a new way for the application of the molecularly imprinted electrochemical sensor in the fields of food and drug detection.