Optically Tunable Bumpy Silver Nanoshells with Size-varied Silica cores: Synthesis and their Surface Enhanced Raman Scattering Characteristics

Abstract

As SERS substrate, noble metal nanostructures on silica core template have been reported by many research groups taking advantages of chemical stability due to silica core. However, as the size of silica core reduces, this benefit is no longer effective. This study reports successful fabrication of silver nanoshells on the amorphous silica nanoparticles (Si NPs) with different core size (59, 82, 103, 124, and 148 nm) by overcoming the increased instability on aggregation during fabrication with a decrease of core size. The problem coming from instability of the small Si NP core in the fabrication processes could be overcome by controlling the kinds of reducing agent, the amount of dispersing agent and the concentration of Si NPs. We obtained localized surface plasmon resonance (LSPR) and SERS spectra from the different sized AgNSs to analyze their size dependent optical properties. AgNSs in all sizes showed broad extinction from the visible to the near infrared (NIR) region, resulting in high SERS enhancement under three different excitation lasers (532, 660, and 785 nm). We introduced the concept of surface roughness as a factor of SERS enhancement in analysis of AgNS, and observed the correlation between the roughness of AgNS and SERS activities. Therefore, these results provide an understanding of size dependent SERS activity for AgNS achieving a base to use and select appropriate AgNS with different sizes depending on the purpose of research.