We report the development of a robust microgel particle platform for the development of surface-enhanced Raman scattering based optical sensors. The microgel particles are comprised of 2-vinyl pyridine (P2VP) and styrene, are characterized and examined as pH-responsive scaffolds to assemble metallic nanoparticles (NPs) for SERS-based detection strategies. The high sensitivity of SERS arises from the enormous enhancement (&gt;10<sup>6</sup>) of the Raman scattering cross sections of molecules that are adsorbed to roughened metal surfaces, such as metallic NP). Anchoring SERS-active NPs to polymer substrates has been explored as a method for improving the reproducibility of the SERS enhancement phenomenon. Microgels of P2VP are promising candidates for such a role owing to the multifunctionality of the pyridine residues located throughout the macromolecular network. In this study, a sterically-stabilized latex consisting of a random copolymer of polystyrene (PS) and P2VP is examined. The dimensions of the latex, and its transition to a microgel are studied by acid-base titration, electron microscopy, dynamic light scattering, and atomic force microscopy. Loading the copolymer microgels with gold NPs through surface chemical reduction is described. The gold NP-loaded microgels exhibit strong SERS-activity that can be used as to sense the local chemical environment by changes in the SERS spectra of adsorbed reporter molecules. These microgel-NP composites are characterized, and their pH-responsive behavior is demonstrated to be reversible at the single-particle level.

Microgel platforms for surface-enhanced Raman scattering based optical probes

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