Rapid one-step synthesis, characterization and functionalization of silica coated gold nanoparticles

This paper describes a rapid, simple and one-step method for preparing silica coated gold (Au@SiO2) nanoparticles with fine tunable silica shell thickness and surface functionalization of the prepared particles with different groups. Monodispersed Au nanoparticles with a mean particle size of 16 nm were prepared by citrate reduction method. Silica coating was carried out by mixing the as prepared Au solution, tetraethoxysilane (TEOS) and ammonia followed by microwave (MW) irradiation. Although there are several ways of coating Au nanoparticles with silica in the literature, each of these needs pre-coating step as well as long reaction duration. The present method is especially useful for giving the opportunity to cover the colloidal Au particles with uniform silica shell within very short time and forgoes the use of a silane coupling agent or pre-coating step before silica coating. Au@SiO2 nanoparticles with wide range of silica shell thickness (5–105 nm) were prepared within 5 min of MW irradiation by changing the concentration of TEOS only. The size uniformity and monodispersity were found to be better compared to the particles prepared by conventional methods, which were confirmed by dynamic light scattering and transmission electron microscopic techniques. The prepared Au@SiO2 nanoparticles were further functionalized with amino, carboxylate, alkyl groups to facilitate the rapid translation of the nanoparticles to a wide range of end applications. The functional groups were identified by XPS, and zeta potential measurements.

Schematic representation of the preparation of silica coated gold (Au@SiO2) nanoparticles by a fast and one-step microwave (MW) method (left). Au@SiO2 nanoparticles with wide range of silica shell thickness (15–105 nm) and good monodispersity were prepared within 5 min of MW irradiation by changing the concentration of TEOS only (right).Figure optionsDownload as PowerPoint slideHighlights
► Silica coated gold nanoparticles (Au@SiO2) were prepared by a fast and one-step microwave method.
► Silica thickness (5–105 nm) was tuned within 5 min by changing tetraethoxysilane loading only.
► Au@SiO2 nanoparticles were functionalized with different groups for many applications.
► Detailed characterization of the prepared samples was carried out by different techniques.