Highly Scattering, Surface-Enhanced Raman Scattering-Active, Metal Nanoparticle-Coated Polymers Prepared via Combined Swelling−Heteroaggregation

We report on a combined swelling−heteroaggregation (CSH) method for preparation of highly scattering, metal nanoparticle(NP)-coated polystyrene (PS) latex beads. This methodology is a facile and relatively benign single-step process for preparation of metal-coated dielectrics for applications in biomedical imaging, sensors, photonics, electronics, and surface-enhanced Raman scattering (SERS). A range of NPs with different sizes (30, 60, and 80 nm), chemistries (gold and silver), and shapes (sphere and cube) were successfully coated on the PS beads by using the CSH procedure. Homogeneous and dense metal coatings on the PS beads were obtained by the addition of tetrahydrofuran (THF) to an aqueous cosuspension of polyvinyl pyrrolidone (PVP) capped-metal NPs and 10 μm PS beads. Composite beads were stable with no loss of the NP coating during long-term (15 months) deionized (DI) water storage. The coating morphology, metal coverage, and optical properties of the composite beads were tunable by simple adjustments in THF and NP compositions as well as the NP chemistry, shape, and size. Dark field microscopy and UV−vis microspectroscopy of single beads showed highly enhanced scattering and tunable optical characteristics. Raman spectroscopy was used to confirm the SERS activity of the composite beads.