(409e) Facile Preparation of Highly-Scattering Metal-Nanoparticle Coated Polystyrene Latex Beads

Noble-metal coated polymer composite microspheres and nanoshells have attracted intense interest due to applications in electronics, photonics, medical imaging, drug delivery, surface-enhanced Raman scattering (SERS) and catalysis. By incorporating nanoparticles (NPs) exhibiting preferential scattering characteristics on a polymeric bead surface, the composite microsphere can be used as a scattering contrast agent for medical imaging, and other optical and electronic devices. Here we report a new technique for the facile preparation of highly-scattering metal NP-coated PS latex beads. Different sizes (30, 60 and 80 nm), chemistries (Au and Ag), and shapes (sphere and cube) of NPs were successfully incorporated on commercially available PS beads using this technique. Homogeneous and dense metal coatings were obtained via solvent-controlled swelling and heteroaggregation of polymer capped-metal NPs with the PS beads by the addition and removal of an organic solvent. The organic solvent controlled the heteroaggregation of colloidal particles as well as the swelling/shrinking mechanism of PS beads in this strategy. No prior functionalization of the bead was needed. The fabricated composite beads were stable during long-term water storage. The morphology and coverage of the metal coating on the beads, and thus optical properties, can be effectively controlled by the proper choice of the concentration of solvent and metal NPs. Complete and close packed metal coating on the PS bead can be obtained with smaller and spherical metal AuNPs, while metal surface coverage reached to a certain limitation with larger or cubic metal NPs. The resulting metal coated-PS microspheres exhibited highly enhanced scattering and tunable optical characteristics, which were investigated with the dark-field microscopy and UV-vis absorption spectra. Their performances as SERS substrates were evaluated with Raman Spectroscopy