Nanoparticles (NPs) with either plasmonic or upconverting properties have been selectively coated onto the surfaces of polystyrene (PS) spheres, imparting their optical properties to the PS colloids. These NP coated PS spheres have many potential applications, such as in medicine as drug-delivery systems or diagnostic tools. To prepare the NP coated PS spheres, gold or core-shell NaYF4Tm0.5Yb30/NaYF4 NPs were synthesized and separately combined with amino-functionalized PS spheres. The mechanism by which the NPs adhered to the PS spheres is attributed to interactions of the NP and a polyvinylpyrrolidone additive with the surfaces of the PS spheres. Two-photon fluorescence microscopy and SERS analysis demonstrate the potential applications of these NP coated PS spheres
