Flow Synthetic Process of SiO₂@Au Core-Shell Nanoparticles by Using Microreactor

Abstract

SiO₂@Au core-shell type particles are quite attractive because of their unique optical properties and potential biomedical applications including imaging, sensing, photothermal therapy, and gene-silencing technology. A widely-used preparation technique of Au nanoshells is the seed-mediated growth, which is composed of three steps: surface modification of core silica particles, Au seeds decoration of the modified silica surface and the shell growth by reduction of Au ions on the Au seeds. Although this technique allows good control in the shell thickness, it takes a long time on the order of days to complete the preparation process. In the present study, we develop a flow synthetic process by applying a microreactor separately to the Au seeds decoration and the shell growth processes. In the decoration process, we demonstrate that the microreactor enables one-step fabrication of gold decorated silica particles by directly reducing Au ions with a strong reducing agent (NaBH₄) in the presence of silica particles, which can remarkably shorten the preparation period. The microreactor flow synthesis is also demonstrated to be effective for the shell growth process when a mild reducing agent (NH₂OH·HCl) is used to suppress the nucleation in the solution phase instead of the Au seeds surface.