Ag@SiO2 Core-Shell Nanoparticles for Probing Spatial Distribution of Electromagnetic Field Enhancement via Surface-Enhanced Raman Scattering

We show that the spatial distribution of the electromagnetic (EM) field enhancement can be probed directly via dynamic evolution of surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) molecules as they diffuse into Ag@SiO2 core-shell nanoparticles. The porous silica shell limits the diffusion of R6G molecules toward Inner Ag cores, thereby allowing direct observation and quantification of the spatial distribution of SERS enhancement as molecules migrate from the low to high EM fields inside the dielectric silica shell. Our experimental evidence is validated by the generalized Mie theory, and the approach can potentially offer a novel platform for further investigating the site and spatial distribution of the EM fields and the EM versus chemical enhancement of SERS due to molecular confinement within the Ag@SiO2 nanoshell.