Abstract
Most investigations for the preparation of imprinted polymers were carried out using purely organic polymers. Organic-inorganic hybrid materials have been found to be highly advantageous as they exhibit flexibility, low density and long shelf life with excellent optical and mechanical properties. The stability and low manufacturing cost makes these hybrid polymers amenable for industrial applications. A synthetic methodology based on sol-gel process, which is one of the fastest emerging fields of material chemistry, is a convenient one for material preparation from organic precursors at ambient temperature. We have adopted two different approaches based on covalent and non-covalent bond interactions with the template molecule. Factors that influenced rebinding of the imprinted polymer including template/monomer ratio, functional monomers, porogenic solvents, temperature and time were explored. The binding selectivity of the MIPs for caffeine and its analogous structures were also discussed. A molar ratio of 1: 4 ~ 8: 20: 30 between CAF: MAAM: VTMOS: TEOS showed maximum of caffeine adsorption capacity whilst the corresponding end capped materials showed better selectivity also. However, the overall capacity reduced considerably because the lack of non-specific interactions due to surface silanol groups. Gel formed in presence of ethanol was more transparent in appearance with maximum selectivity and least affinity towards theophyllline. Prolonged treatment time of MIPs with caffeine solution led to reduction in recognition properties and the optimum was found to be one hour. Saturation of sites reached within 60 minutes. The MIPs showed a maximum adsorption capacity for caffeine at low temperature conditions. So it is advisable to conduct the incubation at low temperature for a maximum of one hour using end capped MIPs samples. For covalent bond interactions with the template molecule, we aim at establishing the technology of polymerization via covalent imprinting, in which cholesterol was employed as the template. The sol-gel polymerization of the complex formed from cholesterol-bound functional monomer and cross-linker were investigated experimentally in detail. The state of the art was achieved by using cholesterol as the template molecule. Several types of cholesteryl (4-vinyl) phenyl carbonate copolymers with vinyltriethoxysilane (VTEOS) or 3-(Methacryloyloxy) propyltrimethoxy silane (MPS) were prepared for cholesterol imprinting. The aforementioned copolymers subjected to sol-gel process with metal alkoxide was generated a hither-to-unknown series of organic - inorganic hybrid materials with nanometer-order ceramic texture. Every effort on the study of polymerization conditions was made to prepare an ideal MIPs, which has a higher stability and adsorption capacity (56%). The technology developed in this study will be very helpful for marketing the molecularly imprinted polymers. In biosensor application study we have demonstrated a novel method for molecular sensing. Synthetic host molecules were made from functionalized CdSe@ZnS nanoparticles by a molecular imprinting process（CdSe@ZnS/MIP-caffeine）. The re-binding experiment of Qdot-MIPs showed a five-fold reduction in emission intensity in its photoluminescence behavior. The observed quenching effects are due to fluorescence resonance energy transfer (FRET), which involves radiationless energy transfer that occurs between QDots and tightly bound guest molecule. The Qdot-MIPs also show a very good selectivity between caffeine and its analogues. The emission intensity of Qdot-MIP is found to be unaffected after the re-binding experiment with theobromine. A similar behavior was observed with theophylline, analogues of caffeine, also. The imprinted sites are highly selective for the template molecule. This was consistent and highly reproducible in the case of other print molecules like uric acid, etc.