Plasmonic nanostructures for unifying surface enhanced Raman and infrared absorption spectroscopy

Plasmon resonances control the electromagnetic near field and far field properties of various metallic nanostructures (e.g. nanoparticles, nanoshells, metallic thin films). The enhanced electromagnetic near field, strongest at the surface of the nanostructures, has been successfully exploited for a variety of surface enhanced spectroscopies. Visible and near-IR surface enhanced Raman spectroscopy (SERS) is an example of such surface enhanced spectroscopic technique that has attracted substantial attention due to its huge enhancement factors (∼ 108-109) and wide range of applications. However, surface enhanced Infrared absorption (SEIRA) spectroscopy, complementary to SERS, has not received nearly the same attention because engineering the necessary strong near fields in the mid-IR is challenging. This thesis is an effort for developing rationally designed Au nanoshell based substrates for SEIRA and for combining SERS and SEIRA to unify the field of surface enhanced vibrational spectroscopy for comprehensive biochemical sensing applications. Specifically, this thesis describes the utilization of inteparticle junction hot spots for SEIRA. Aggregates of near---IR resonant nanoshells with naturally occurring junction hot spots are demonstrated to be excellent SEIRA substrates with high enhancement factors (103-104 ). Applications of SEIRA in conjunction with SERS (exploiting near fields from single particle plasmon of nanoshells) is demonstrated for a variety of biologically relevant processes such as adsorption, local orientation and binding of adenine and adeninemonophosphate (AMP) on Au nanoshell surface, intercalation of ibuprofen in hybrid lipid membranes, and lipid transfer/exchange between hybrid lipid bilayers and vesicles. Finally, the random aggregate geometry for SEIRA is elegantly extended into 2D periodic array of nanoshells that truly unifies SERS and SEIRA on a common single substrate by simultaneously enhancing both Raman and Infrared signals in two diverse frequency regimes with high spectral sensitivity.