Surface modification of polymeric microspheres by gold nanoparticles

The role of the polymer nature and surface functionality in the modification of polymeric microspheres by gold nanoparticles was investigated. Monodisperse cross-linked polymer microspheres with diameters up to 5 μm were prepared by core/shell heterophase polymerization with the use of seeding polystyrene cores and styrene, divinylbenzene, or ethylene glycol dimethacrylate as monomers. The deposition of gold nanoparticles on the surface of microspheres from aqueous solutions containing H[AuCl4] was carried out by photochemical reduction with UV light, by chemical reduction with sodium citrate, or by both methods used in sequence. Electron microscopy showed that gold photoreduction in polymer dispersions mainly occurs on the polymer surface and that gold nanoparticles smaller than 40 nm have narrow size distributions. Carboxylic and thiol surface groups forming salts with metal ions act as sites for the following nucleation of Au atoms to form clusters; nanoparticles; and, finally, continuous gold layers.