Nanoporous Microcantilevers with Plasmonic Absorbers for Photothermal Infrared Spectroscopy

Abstract

A nanoporous anodic aluminum oxide (AAO) bimetallic cantilever enhanced by a gold coating on the nanopores creates a plasmonic crystal structure. The fabricated sensor is used for photothermal cantilever deflection spectroscopy (PCDS). Explosive compounds tested, showed spectra identifying explosive compounds by their characteristic wavelengths. Through a two-step anodization process, photolithography, and bimetallic and plasmonic coatings, a sensitive photothermal microcantilever was fabricated. The bimetallic layer thickness was optimized through analytical calculations. The ideal plasmonic layer thickness was found through experimentation. Molecules adsorbed onto the cantilever surface had their mass quantified through a measured change in 2nd mode resonant frequency. Simultaneously, the molecules were identified by high power infrared (IR) spectroscopy. For standoff spectroscopy, a plasmonic enhanced AAO cantilever was shown to improve characteristic peak depth 10-fold and 7-fold compared to silicon and AAO bimetallic cantilevers, respectively. The limit of detection (LOD) of the plasmonic AAO cantilever was determined to be 63.42 ng/cm2.