Dye fluorescence enhancement by plasmonic nanostructured gold–titania film composites obtained by the combination of electrodeposition and surface sol-gel process

Plasmonic nanostructured gold–titania film composites were fabricated and evaluated their dye fluorescence enhancement properties. The plasmonic nanostructured gold was fabricated by electrodeposition. The ragged and overlapped particle structures were observed in the nanostructured-gold. The sizes of the deposited structures varied from several tens of nanometers to the submicrometer level. Titania thin films were prepared via the self-assembly of thiols on the nanostructured-gold and a surface sol-gel process. Formation of the plasmonic nanostructured gold–titania film composites was confirmed by X-ray photoelectron spectroscopy. Porphyrin dye was deposited as a fluorescent probe on the outermost layer of the titania film. The degrees of ground-state excitation of porphyrin dye by plasmonic electric fields were evaluated in various composites with different numbers of repetitions (1–40 times) of surface sol-gel processes for titania layer formation. The enhancement ratios of porphyrin varied with the thickness of the titania film, which functioned as a spacer. In particular, apparent fluorescence enhancement of the porphyrin dye was observed at wavelengths longer than 550 nm using the composites. Graphical abstract