Numerical investigations of Au@SiO2 dimers for shell-isolated nanoparticles enhanced Raman scattering and fluorescence

Abstract

The shell-isolated nanoparticles (SHINs) has developing into a hot research topic and been extensively applied in optical spectroscopy, especially, surface enhanced Raman scattering (SERS) and fluorescence (SEF) spectra. Herein, the SERS and SEF effect of a general model molecule located at the nanogap formed in the center of Au@SiO2 dimers were systematically studied for understanding the electromagnetic (EM) enhancement mechanism. The EM enhancement, quantum yield, Raman and fluorescence enhancement of Au@SiO2 dimers with different core radius and shell thickness were investigated and analyzed successfully by using the three-dimensional finite element method (3D-FEM). The simulation results show that the nanogap of Au@SiO2 dimers could provide the stronger SERS and SEF enhancement. The SERS effect strongly related to EM enhancement, while the SEF effect mainly depended on the competition between EM enhancement and fluorescence quantum yield, both of which could be tuned by the core radius, dimer distance and shell thickness. The maximum Raman and fluorescence enhancement as predicted by the theoretical calculation can be as high as 9 and 4 orders of magnitude with an optimal radius of 50 nm, dimer distance of 1 nm and shell thickness of 1 nm under 633 nm laser excitation, respectively. We expect the results could improve the sensitivity of detection in the application of SERS and SEF technology.