Molecular imprinting of azobenzene carboxylic acid on a TiO₂ ultrathin film by the surface sol-gel process

Ultrathin films of titanium oxide gel imprinted with 4-(4-propyloxyphenylazo)benzoic acid (C₃AzoCC₂H) were prepared by repeated immersion of a gold-coated quartz crystal microbalance (QCM) electrode or a quartz plate in solutions of C₃AzoCO₂H and titanium butoxide (Ti(O-nBu)₄) in toluene/ethanol. Regular film growth was confirmed by frequency decrement in QCM measurements and by the appearance of the azobenzene absorption in UV-vis spectroscopy. The template molecule could be completely removed upon treatment with 1% aqueous ammonia. The resulting films showed saturation binding of the template molecule in acetonitrile in less than 1 min. Binding of the template molecule was greatest among aromatic carboxylic acids that are structurally related to the template. A related ester showed a significant reduction in the binding efficiency. The surface sol-gel process provides a powerful tool for molecular imprinting in ultrathin metal oxide films.