Surfactant-free galvanic replacement for synthesis of raspberry-like silver nanostructure pattern with multiple hot-spots as sensitive and reproducible SERS substrates

Abstract

Using a galvanic replacement (GR) reaction in the absence of surfactant as a stabilizer, we report a robust synthesis of raspberry-like silver nanostructure pattern with multiple “hot-spots”. First, uniform copper nanodisk patterns were generated on Pt layer via nano imprint lithography and Ag+ ions were added for reaction. The Ag+ ions selectively oxidized Cu atoms, because of the reduction potential variance. The uncovered Cu surface promoted contact between Cu atoms and Ag+ ions to synthesize a sufficient quantity of silver nanostructures on copper nanodisks to generate multiple strong “hot-spots”. However, coating the copper nanodisk with surfactant impeded the progress of the GR reaction and failed to synthesize “hot-spots”. Due to metal bonding between the metal nanostructures and Pt layer, the synthesized silver nanostructure pattern preserved mono-dispersity and stability. We demonstrated applications for rapid detection of Rhodamine 6G (R6G) molecules by surface-enhanced Raman scattering spectroscopy (SERS) with low detection limit (10−12 M) and excellent signal uniformity (RSD < 8.3 ± 1.3%). Since surfactants have been considered as important pre-requisites in GR reactions for stability of nanostructures, the findings reported here offer a new opportunity for synthesizing various kinds of metal nanostructures via GR and expanding their applications.