Metal/conductive oxide plasmonic structures for surface-enhanced infrared absorption spectroscopy

Surface-Enhanced Infrared Absorption (SEIRA) is a phenomena in which vibrational signals from trace amounts of analyte or sub-monolayer molecules adsorbed on solid surfaces are dramatically enhanced in their intensities. By utilizing the localized surface plasmon resonances of infrared optical antennas and metamaterials, strong signal enhancements of molecules become operative in an effective manner to realize high sensitivity vibrational sensing. Recent developments in nanostructure fabrication techniques as well as their surface functionalization techniques have enabled us to propose and fabricate various types of advanced SEIRA nanodevices in nanophotonics and in nano-biosensing fields as well as in analytical chemistry. Moreover, recent advances in searching appropriate infrared plasmonic materials beyond noble metals have widened the possibilities to utilize low-cost base metal and conductive metal oxides for SEIRA applications. In this review article, we introduce the detection of dilute molecules and pathogenic enzymes in solution by an in situ ATR-IR method, as well as protein SEIRA sensing by surface-functionalized Al optical antennas and metamaterials. We also introduce our new approach to utilize infrared surface plasmons in optical antenna array made of phosphonic acid-functionalized conductive oxide nanorods to detect proteins with high specificity and sensitivity.