Synthesis, characterization and surface enhanced Raman scattering of hollow gold–silica double shell nanostructures

Abstract

Hollow gold-silica double-shell (HGSDS) and hollow gold-silica composite (HGSC) nanostructures have been synthesized and their structural, optical, and surface-enhanced Raman scattering (SERS) properties have been characterized. The structure of the HGSDS and HGSC was determined by scanning transmission electron microscopy (STEM) and high- resolution transmission electron microscopy (HRTEM). STEM images of the HGSDS reveal a reasonably uniform diameter of approximately 500-1000 nm with SiO2 deposited, using a modified Stober method, onto aggregated structures of hollow gold nanospheres (HGNs). The HGSC structures were determined to be 30 nm in size by HRTEM. The broad surface plasmon resonance (SPR) absorption of both the HGSDS and HGSC structures is dominated by gold but concomitantly influenced by the silica, with the peak position blue-shifted by ∼100 nm relative to that of the starting HGNs. The broad and tunable SPR band can be useful for applications such as SERS. As a preliminary demonstration, SERS studies of Rhodamine 6G (R6G) and β-glucose have been carried out. The results show reproducible detection with limits as low as 0.9 and 5 mM, respectively. Glucose has traditionally been difficult to detect with SERS due to its small Raman cross-section and low SERS signal arising from weak interaction with the metal substrate. Compared to HGNs, the SERS signal of β-glucose using HGSDS and HGSC is enhanced, which is attributed to the relatively strong interaction between the glucose and the SiO2 surface. These results demonstrate that the silica-modified HGN structures are both interesting and useful as a result of their unique structural and optical properties.