Single-Molecule Surface-Enhanced Raman Scattering Sensitivity of Ag-Core Au-Shell Nanoparticles: Revealed by Bi-Analyte Method.

Single-molecule surface-enhanced Raman scattering (SM-SERS) is an important application of localized surface plasmons in metallic nanostructures. Conventionally, Ag nanoparticles are used in solution-based SM-SERS experiments, but their usage is limited due to toxicity and oxidation issues. Au nanoparticle solutions are relatively biocompatible and SERS-active, but they do not facilitate large-scale SERS enhancement factors, which is an important prerequisite for SM-SERS. Under such constraints, silver-core gold-shell nanoparticles can be an excellent alternative for SM-SERS. Motivated by this, herein we report on the experimental evidence of SM-SERS sensitivity of Ag-core Au-shell nanoparticles by employing bianalyte method. Additionally, by detecting resonant molecules at femtomolar concentrations, we show that Ag-core Au-shell nanoparticle can be harnessed for ultrasensitive detection of molecules. The provided evidence will further motivate usage of such gold-shell-based bimetallic nanostructures for SM-SERS in biological environments.