Dimeric Core–Shell Ag2@TiO2 Nanoparticles for Off-Resonance Raman Study of the TiO2–N719 Interface

In this paper, we present a nanoparticle-enhanced Raman spectroscopic study of TiO2–N719 (bis(tetrabutylammonium) [cis-di(thiocyanato)-bis (2,2′-bipyridyl-4′-carboxylate-4-carboxylic acid)-ruthenium(II)])) interface by employing Ag2@TiO2 dimeric core–shell nanoparticles, where the TiO2 shell serves as an active semiconductor surface. The Ag2@TiO2 nanoparticles are synthesized by connecting two Ag nanoparticles with thiol-modified complementary DNAs, followed by coating a 2 nm thin layer of TiO2 on the Ag2 dimeric nanoparticles. The Ag2@TiO2 dimeric core–shell nanoparticles show a red-shift of plasmon resonance frequency compared with Ag@TiO2 core–shell nanoparticles, and provide significant SERS enhancement over the Ag@TiO2 nanoparticles, which allows for the investigation of SERS of TiO2–N719 interface under off-resonance conditions using low energy 785 nm laser excitation. Fine potential dependent Raman measurements show that thiocyano and carboxyl groups of the N719 molecule can adsorb on the TiO2 shel...