Western CEDAR

pH-Dependent Surface-Enhanced Raman Scattering Response of Control Growth Au Nanoparticle Loaded Microgel Particles

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive spectroscopic technique for analyzing and detecting simple molecular mixtures to complex collections of molecules or biological structures. The high sensitivity of SERS arises from the enormous enhancement (>10⁶) of the Raman scattering cross sections of molecules that are adsorbed to roughened metal surfaces, such as metallic nanoparticles (NPs). Anchoring SERS-active NPs to polymer substrates has been explored as a method for improving the reproducibility of the SERS enhancement phenomenon. Microgels of poly(2-vinylpyridine) (P2VP) are promising candidates for such a role owing to the multifunctionality of the pyridine residues located throughout the macromolecular network. We will present a study of the synthesis of a sterically-stabilized latex consisting of a random copolymer of polystyrene (PS) and P2VP. The dimensions of the latex, and its transition to a microgel are studied by acid-base titration and monitored by dynamic light scattering. Loading the copolymer microgels with Au NP seeds through surface adsorption is also described. A controlled growth synthesis of the seeds is used to optimize the enhancement factors for SERS. The Au NP-loaded microgels exhibited SERS-activity demonstrated by detection of pyridinyl groups in the polymer support as well as for a dissolved analyte. A reversible pH-dependent response for the intensity of the SERS spectra for dissolved analyte is observed.