FEM investigation of Cu@SiO2 core-shell nanoparticle for a sensitive and low-cost SERS and SEF substrate

We theoretically investigate the plasmon coupling properties of Cu@SiO2 core-shell system that supports the measurement of surface enhanced Raman spectroscopy (SERS) and surface enhanced fluorescence (SEF) technology. The roles of Cu core and SiO2 shell in tuning LSPR have been quantitatively discussed by calculating the localized electric field enhancement factor (EF), fluorescent quantum yield, SERS and SEF EF in the nanogap based on finite element simulations. In this work, we demonstrate that the SERS and SEF effect strongly depend on the core size, shell thickness and dimer distance. The larger size of Cu core, ultrathin thickness of SiO2 shell and shorter dimer distance could be considered as the ideal substrate. Meanwhile, the strong localized excitation enhancement is a vital contribution to fluorescence spectral. By comparison, it is found that the enhancement effect of the Cu, Au and Ag cores are very close in order of magnitude in the red and near infrared regions, and thus the low-cost Cu core may act as an active substrate in these regions. At the excitation wavelength of 630 nm, the optimized core size of 60 nm and shell thickness of 1 nm provide the maximum Raman and fluorescence EF as high as 9 and 4 orders of magnitude. Our theoretical results not only help understanding the underlying enhancement mechanism for the core-shell SERS and SEF effect, but also contribute to develop the low-cost and sensitive detection technology.