Tuning plasmonic properties by promoting the inward Hg diffusion oxygen plasma treatment in gold nanorods coated with a mesoporous silica shell.

This paper describes a new strategy using oxygen plasma treatment to tune the localized surface plasmon resonance (LSPR) of gold nanorods coated with a mesoporous silica shell (AuNRs@SiO) exposed to mercury (Hg) solution. Dark-field (DF) microscopy and spectroscopy were used to reveal the effects of oxygen plasma treatment on the structural and LSPR spectral changes of single amalgamated AuNRs@SiO. Due to the structural stability provided by the mesoporous silica shell, the amalgamated AuNRs@SiO exposed to oxygen plasma treatment showed no morphological transformation. Furthermore, real-time monitoring of single AuNRs@SiO showed slow Hg inward diffusion into AuNR cores in air over a long timeframe (24 h), as revealed by the redshift and linewidth narrowing of the LSPR peak. However, the oxygen plasma treatment resulted in faster inward diffusion of Hg into AuNR cores within 20 min, almost 60 times faster than the amalgamated AuNRs@SiO untreated with oxygen plasma. Thus, oxygen plasma treatment was further presented as a new effective approach to control the LSPR properties by promoting the inward Hg diffusion in amalgamated AuNRs@SiO without structural deformation.