Synthesis of Water-Soluble and Functionalized Nanoparticles by Silica Coating

Synthetic methods for high-quality near-monodispersed nanoparticles of metals, metal oxides, and quantum dots in organic solvents are well-developed, but their applications are restricted due to the lack of water solubility and tailored surface chemistry. In this work, we report the silica-coating procedure for various hydrophobic nanoparticles, including Au, Ag, Fe3O4, and ZnS−CdSe to derive water-soluble and functionalized nanoparticles. We have developed a silica-coating method in toluene using commercially available silanes. This approach is applicable to hydrophobic nanoparticles in the size range of 2−20 nm. Silica-coated nanoparticles are 10−30 nm in size, water-soluble, buffer-stable, and have a positive or negative surface charge depending on the surface functional group and solution pH. The coated particles have primary amine groups on the outer surface and are further functionalized with biotin and antibody.