Single-Particle Study on Hg Amalgamation Mechanism and Slow Inward Diffusion in Mesoporous Silica-Coated Gold Nanorods without Structural Deformation

Abstract

This paper presents the structural and spectral variations of individual mesoporous silica-coated gold nanorods (AuNRs@mSiO₂) compared to bare AuNRs upon Hg-Au amalgamation. First, the aspect ratio of AuNRs@mSiO₂ exposed to Hg solutions was unchanged because the deformation related to the cores of AuNR was suppressed by the silica shell. Second, dark-field microscopy and spectroscopy revealed a blue shift of the localized surface plasmon resonance (LSPR) wavelength peak and strong plasmon damping in the individual AuNRs@mSiO₂ scattering spectra, exposed to Hg solutions. Furthermore, we investigated time-dependent adsorption kinetics and spectral changes during the formation of Au-Hg amalgam in single AuNRs@mSiO₂ over a long time frame without any disturbance from the structural deformation. The inward Hg diffusion into the AuNR core caused a gradual red shift and line width narrowing of the LSPR peak when AuNRs@mSiO₂ were withdrawn from Hg solution. Thus, this paper provides new insights into the relationship among amalgamation process, morphological change, the role of silica shell, Hg inward diffusion, LSPR peak, and line width at the single-particle level.