The effect of silica shell on the surface enhanced Raman scattering and fluorescence with Ag nanoparticles: A three-dimensional finite element method investigation

Shell-isolated nanoparticles has recently been extensively applied in surface-enhanced Raman scattering (SERS) and fluorescence (SEF) studies. In the present work, we study the SERS and SEF effect of a general model molecule placed in the middle of silica coated silver nanoparticle dimers (Ag@SiO2) for better understanding of the enhancement mechanism. The electromagnetic (EM) enhancement and fluorescence quantum yield of Ag@SiO2 dimers were simulated by using three-dimensional finite element method, and then the Raman and fluorescence enhancement factors were obtained. The influence of the size of the Ag core and the thickness of the SiO2 shell were systematically investigated and analyzed. The simulation results show that Ag@SiO2 dimers can provide the better hot spots for SERS and SEF detection when compared with bare Ag nanoparticles. It was found that the SiO2 shell can efficiently transmit the strong EM enhancement from the Ag core, and it also exhibited better fluorescence enhancement when compared to the uncoated Ag dimers. The maximum enhancement to the SERS and SEF signals as predicted by the numerical simulations are found to be around ∼109 and ∼104 with excitation wavelength of 500 nm, respectively.