Disclosed are silica-coated nanoparticles and a process for producing silica-coated nanoparticles. Silica-coated nanoparticles are prepared by precipitating nano-sized cores from reagents dissolved in the aqueous compartment of a water-in-oil microemulsion. A reactive silicate is added to coat the cores with silica. Also disclosed are methods for functionalizing silica-coated nanoparticles for use in a variety of applications.