Preparation Of Molecularly Imprinted Electrochemical Sensors Based On Porous Materials And Their Applications In Food Safety Detection

With the development of the time,people's demands for living standards have become higher and the safe of environment and food have become more important.Pesticide and hormones are often used to increase the yield of agricultural products,and antibiotics are often used in animal husbandry and agriculture to treat various bacterial infections and suppress pathogenic microbial infections.2,4-Dichlorophenoxyacetic acid(2,4-D)is a plant hormone that promotes plant growth at low concentrations and acts as a herbicide at high concentrations.The residual of 2,4-D in crops increased because of the abuse of pesticides,which posing a health threat to human due to its genotoxicity and endocrine disruption properties.Metronidazole(MNZ)is the product of microbial metabolism can kill and inhibit the growth of microorganisms.In recent years,the residues in food has increased because of the widespread application of antibiotics.However,MNZ shows genotoxic,carcinogenic and mutagenic side effects,so its application in aquaculture and farming industries has been prohibited by many countries and areas.Therefore,the detection of pesticide and antibiotics is important,but traditional methods for detecting pesticide and antibiotics have some limitations including time-consuming,complicated equipment and the consumption of large amounts of organic reagents.Therefore,it is necessary to explore a sensitive and efficient method for the detection of hormones and antibiotic residues in food.Molecularly imprinted polymers have high affinity and specific recognition capabilities for target molecules,and have good storage stability and reusability.Porous materials show high surface area which can provide more imprinting sites for molecular imprinting,and is conducive to enhancing mass transfer.In this study,molecularly imprinted electrochemical sensor for the detection of 2,4-D and MNZ constructed based on the molecular imprinting technique combined with various nanomaterials.These sensors show advantages of low detection limit,high selectivity,good stability and convenient operation,and can be used for the detection of real samples.Part I Molecularly Imprinted Electrochemical Sensor for 2,4-D Detection Based on Hierarchical Porous Silica NanoparticleAmino-functionalized hierarchical porous silica(HPSNs-NH2)particles were synthesized successfully by using tetraethyl orthosilicate as the silica source,cationic surfactant cetyltrimethylammonium bromide as the structure-directing agent and 3-aminopropyltriethoxysilane as the aminosilane coupling agent in water-ethanol-ethyl ether ternary-solvent system.It was used as a molecularly imprinted matrix and molecularly imprinted polymer(MIP)was prepared by electrochemical polymerization with 2,4-D as a template and o-phenylenediamine(OPD)as a monomer.The MIP was used for the detection of 2,4-D.The results illustrated that the molecularly imprinted electrochemical sensor constructed by HPSNs-NH2 showed a good response to 2,4-D.Under the optimal conditions,the the range of 2,4-D detection was from 1.00×10-10 to 2.50×10-8 mol L-1 and the detection limit was 1.17×10-11 mol L-1(3Sa/b).The prepared sensor has high specificity,sensitivity and good reproducibility for the determination of 2,4-D and the results of actual sample were also satisfactory.Part II Molecularly Imprinted Electrochemical Sensors for 2,4-D Detection Based on Porous GrapheneA kind of porous graphene has been prepared by using graphene oxide(GO)sheets prepared by modified Hummers' method as precursor,sodium citrate as reductant and chitosan was added.It was obtained by a hydrothermal reaction and a freeze-drying process.It was used as a molecularly imprinted matrix and molecularly imprinted polymer(MIP)was prepared by electrochemical polymerization with 2,4-D as a template and OPD as a monomer.The material was used for molecular imprinting and electrochemical detection,and the sensor showed good response to 2,4-D.The detection sensitivity can be improveed because of the porous graphene has good conductivity.Under the optimal conditions,the range of 2,4-D detection was from 5.00×10-11 to 2.50×10-8 mol L-1 and the detection limit was 7.82×10-12 mol L-1(3Sa/b).The MIP electrochemical sensor prepared by this method can be used for the determination of 2,4-D in the real sample and the results were satisfactory.Part III Molecularly Imprinted Electrochemical Sensors for MNZ Detection Based on Mesoporous Bioactive GlassesMesoporous bioactive glasses(MBGs)were prepared by removing the template using ethyl orthosilicate as a silicon source and ordered macroporous carbon(OMC)as a template.The prepared material was used to construct molecularly imprinted electrochemical sensor for the detection of MNZ and showed good response.Under the optimal conditions,the range of MNZ detection was from 1.00×10-10 to 1.00×10-8 mol L-1 and the detection limit was 3.39×10-11 mol L-1(3Sa/b).The electrochemical sensor can be used for the detection of MNZ in the real honey sample and the results were satisfactory.