Regioselective imprinting of anthracenecarboxylic acids onto TiO2 gel ultrathin films: an approach to thin film sensor

Ultrathin films of titanium oxide gel were imprinted with aromatic carboxylic acids, e.g. 4-(4-propyloxyphenylazo)-benzoic acid (C3AzoCO2H) and anthracenecarboxylic acids (2-AnCO2H and 9-AnCO2H), by repeatedly immersing a gold-coated quartz crystal microbalance (QCM) electrode or a quartz plate in a mixed solution of given carboxylic acids and titanium-n-butoxide (Ti(O-nBu)4) in toluene/ethanol. Regular film growth was confirmed by frequency shifts of QCM measurement and by appearance of the absorption for aromatic moieties in UV-visible spectroscopy. The template molecules were completely removed upon treatment with 1% ammonia solution. The resulting films showed sensitive mass increases for guest binding of various carboxylic acids, and the isomeric structure of the two anthracenecarboxylic acids (2- and 9-isomers) was discriminated by the imprinted films. Together with our previous results, major molecular selectivities-functional selectivity, structural selectivity, regioselectivity, and enantioselectivity-are all achieved by imprinted TiO2 gel films.