Facile preparation of highly-scattering metal nanoparticle-coated polymer microbeads and their surface plasmon resonance

We report on the facile preparation of highly scattering metal-coated polystyrene (PS) latex beads by using solvent-controlled heterocoagulation. Starting with an aqueous dispersion of PS beads and poly(vinyl pyrrolidone)-capped metal nanoparticles (NPs), homogeneous and dense metal coatings were obtained by the controlled addition and removal of tetrahydrofuran (THF). Different sizes (30, 60, and 80 nm), chemistries (gold and silver), and shapes (sphere and cube) of NPs were successfully incorporated on commercially available PS beads. The resulting metal coated-PS microspheres exhibited highly enhanced scattering and tunable optical characteristics useful for biomedical imaging, sensors, and opto-electronic devices. The fabricated composite beads were stable, with no loss of metal coating, during long-term water storage. The morphology and coverage of the metal coating, and the bead's optical properties, were controllable over a wide range by the concentration of THF and metal NP, and NP size, shape, and chemistry.