Flow microreactor synthesis of gold nanoshells and patchy particles

•We synthesize silica@Au core-shell and patchy particles using a microreactor.•We use selective nucleation and subsequent growth on core particle surface.•We demonstrate that our technique produces uniform nanoshells and patchy particles.•Shell structure can be controlled by the type of reducing agents.

Silica@Au core-shell type composite particles are promising for biomedical applications due to their unique optical and chemical characteristics, although the problem lies in the synthetic processes. They are typically synthesized via batch type reactions including multiple steps, and the complexity in the synthetic process is an obstacle to practical applications. A robust and facile process is thus required. In the present study, we developed a flow synthetic process by applying a microreactor with a high mixing performance to silica@Au nanoshells and patchy particles. Following a concept of selective nucleation and subsequent growth of the gold on the core surface, we mixed a suspension of surface-modified silica particles containing gold ions with a reducing agent solution in the microreactor, and investigated the effects of the core particle size and the type of reducing agents on the composite particle synthesis. Through the investigation, we found that the ratio of the gold ion amount to the surface area of core particles is a key factor for obtaining uniform core-shell particles. In addition, the morphology of gold formed on the core surface was demonstrated to change from spherical nanoparticles to dendritic patches depending on the reducing ability of reducing agents.

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