Analysis of core-shell-isolated nanoparticle configurations used in the surface-enhanced raman scattering technique

Core-shell-isolated nanoparticles are commonly used in the surface-enhanced Raman scattering (SERS) technique to detect binding events and in analyte identification at the molecule level. In this paper, an opticalscattering theoretical model was used in which the core-shell-isolated nanoparticles are considerably smaller than incident light wavelengths, and the finite difference time domain method of numerical electromagnetics was adopted to compute the scattered opticalpower density per unit volume of the nanoparticles. In addition, the power densities were analyzed using various shell materials and the influences of differing parameters (i.e., the size of metal nanoparticles, shell thickness, nanoparticle size, and the distance between nanoparticles) on power-density functions were explored. The results indicated that when the nanoparticle shells were coated with silicon dioxide (SiO₂) and aluminum oxide (Al₂O₃) to a thickness of 1 nm and the nanoparticle core was gold (Au), a particle size of 35 nm was the optimal design. The optimal distance between Au nanoparticles possessing SiO₂ shells was 5 nm and that between Au nanoparticles possessing Al ₂O₃ or titanium dioxide (TiO₂) shells was 10 nm. Based on the format results of nanoparticle arrangement, the distance between the shell-isolated Au nanoparticles was 10 nm and generated a stronger scattered power density with an asymmetric arrangement than that generated using symmetrically arranged nanoparticles. The advantage of the proposed method in this paper over the conventional method is its ability to relate the scattered power density to the required number of nanoparticles used in the SERS technique.