APPLICATIONS OF SILVER ISLAND FILMS FOR THE PREPARATION OF FLUORESCENTLY BASED CHEMICAL SENSORS

The use of silver island films in the design and construction of fluorescently based sensors is examined in conjunction with the fluorophores nitrobenzoxadiazole (NBD) and 6-tetramethylrhodamine-thiocarbamoyl (TRITC), which are covalently attached at the head group of the lipid dipalmitoyl-L-phosphatidyl-ethanolamine (PE). Behenic acid (BA) monolayers containing 0.1 - 1 mol% of each fluorophore are deposited by Langmuir- Blodgett (LB) techniques onto glass, 40 angstrom thick silver island films and 1600 angstrom thick smooth silver films. Fluorescence is observed for both NBD and TRITC films deposited onto silver island films with average island diameters greater than 200 angstrom. Relative to the glass surface, significant fluorescence quenching of NBD is observed on the silver island films, while a slight enhancement of fluorescence is observed for the 0.5 mol% TRITC film. Very little or no fluorescence is observed for systems with island diameters less than 200 angstrom, and no fluorescence is observed from smooth silver films. The fluorescence response resulting from structural changes in a 1 mol% NBD-PE/BA monolayer deposited on a glass surface and a bilayer deposited on a silver island surface induced by exposure to water vapour and a mixture of water and acetic acid vapour is examined. Both systems respond in a reproducible and reversible manner upon hydration, but an amplified fluorescence response is observed for the silver island surface. Partitioning of acetic acid into the bilayer on the silver island surface further amplifies the fluorescence response to subsequent hydration.