Molecular imprinting of caffeine and its recognition assay by quartz-crystal microbalance

Phase inversion precipitation method was applied to prepare molecularly imprinted polyacrilonitrile (PAN) copolymers. Three types of PAN copolymers with pyridine and styrene moieties were used for caffeine (CAF) imprinting. For encoding shape of the template molecules into the polymer, polymer solution involving the template molecule was coagulated in water non-solvent. After the template extraction from the resultant polymer, binding amounts of CAF and CAF analogous molecules to the CAF-imprinted polymer were evaluated by using 6 MHz quartz-crystal microbalance (QCM). As QCM attached with CAF-imprinted polymer was immersed into CAF solution, the QCM frequency decreased and then saturated at constant value. We demonstrated recognition properties of the CAFimprinted polymers by observation of the frequency change for various imprinted and unimprinted polymers. It was observed that PAN copolymer having 4-vinylpyridine (4-Py) moieties showed a large difference of the frequency decrease between the imprinted and unimprinted polymers. Evidence was presented that the CAF-imprinted polymer having 4-Py moieties highly recognize CAF molecules. Also, the selectivity of the CAF-imprinted polymers was investigated using CAF analogous molecules.