The present invention represents a radical departure from most conventional macro-scale batch processing methods employed to synthesize and coat colloidal nanoparticles. Synthesis and coating are in series and in-situ, obviating the need for numerous cumbersome, and often expensive intermediate-processing steps. In one embodiment, the invention is a method and apparatus for synthesizing colloidal nanoparticles. In another embodiment, the invention is a method and apparatus for enabling coating of colloidal nanoparticles using an electrophoretic switch for contacting and separating said colloid nanoparticles.