Silver nanoparticles deposited on TiO2-coated cicada and butterfly wings as naturally inspired SERS substrates

Abstract

Ag nanoparticles were photocatalytically deposited on TiO₂-coated cicada and butterfly wings (Ag/TiO₂-coated wings). Wings of two species of cicadas (Cryptotympana facialis and Graptopsaltria nigrofuscata) and one species of butterfly (Parnassius citrinarius) were investigated as substrates based on natural materials. Uniform ordered nanopillar arrays and irregular sub-micron sized pillar structures were observed on the wing surfaces of Cryptotympana facialis and Graptopsaltria nigrofuscata, respectively. On the surface of wing scales of Parnassius citrinarius, a uniform ordered ridge structure was observed. A small number of Ag nanoparticles were also deposited on the intact bare cicada and butterfly wings without TiO₂ (Ag/wings) by photoreduction. The surface enhanced Raman scattering (SERS) signal intensities of rhodamine 6G (R6G) dripped and dried on the Ag thin film sputtered on glass slides, Ag/wings and Ag/TiO₂-coated wings increased in that order. In particular, the SERS signal intensities of R6G on the Ag/TiO₂-coated wing of Cryptotympana facialis were more than 25 times larger than those on the Ag thin film.