Molecular Imprinted Polymer Coated Electrochemical Sensors for Evaluation of Biological and Environmental Samples

Abstract

Molecularly imprinted polymers (MIPs) are synthetic polymers which mimic recognition properties of natural receptors. The natural receptors although exhibit excellent binding properties and selectivity, but these are unstable out of their native environment. Also their production is expensive and low in yield. Thus, to replace natural affinity molecules, molecular imprinted polymers were fabricated. MIPs possess imprinted cavities which have sterical and functional complementary with target compounds. MIPs are synthesized by mixing target compound, monomer and crosslinker in porogen and polymerization is initiated thermally, photolitically or electropolymerization is performed. Templates are washed out after polymerization leaving affinity cavities in polymer. These can bind target compound more selectively due to inherent predetermined selectivity of MIPs. MIPs offer various advantages over natural receptors such as easy fabrication, stable in harsh acidic/basic environment, can be stored at room temperature, cost effective and selective. The main objective of this work was to fabricate such imprinted polymers which are economical, lesser preparation time and exhibit superior performance in sensing various compounds of analytical importance. Traditionally polymers are synthesized using free radical polymerization. Higher temperatures in polymerization result in reduced selectivity and low affinity. Photopolymerization being able to carry at ambient conditions is an appropriate alternative. Lower temperatures in photopolymerization contribute to entropic stability and more stable prepolymerization complexes are formed. This eventually results in high affinity binding cavities, which are rigid, more homogenous and resulting polymer has higher surface area and thermally stable with improved selectivity and sensitivity. MIP when combined with transducer (electrode) as a sensing probe can enhance detection limits upto nano and microgram levels. In this thesis, comparative performance of thermally and photopolymerized MIP was investigated for 4-NP electroreduction by voltammetric techniques. Adsorption studies were also performed investigate adsorption capacity and binding kinetics of these imprinted polymers. The performance of imprinted polymers was compared with non imprinted polymers also, revealing high selectivity of imprinted polymers due to conformational cavities already imprinted in them. The imprinted polymer for fluoxetine antidepressant drug was also synthesized and fluoxetine determination was optimized by analytical and technical parameters. The imprinted polymers showed better recognition properties as compared to controls, owing to predetermined selectivity of MIP. The synthesized imprinted polymers can be potentially used for real sample analysis (water and serum) with improved limit of detection even in presence of structural analogues of target compound as interferents. Thus, imprinted polymers can be used in real life applications.