Silica Shell Growth on Vitreophobic Gold Nanoparticles Probed by Plasmon Resonance Dynamics

The early stages of silica deposition on vitreophobic citrate-capped gold nanoparticles (AuNPs) are studied using in situ optical spectroscopy supported by electron microscopy and hydrodynamic size measurements. Through extinction spectra fitting, the time dependence of the surface plasmon resonance, which acts as a sensitive probe of the local environment, reveals three distinct stages of uniform silica shell formation on AuNPs. The first stage, which has not previously been reported, is characterized by an increase in plasmon damping by adsorption of silica precursors. The initial silica growth is shown by electron microscopy to be highly anisotropic, proceeding radially from the vertices of the faceted AuNPs before forming conformal shells.