Abstract
Plasmonic nanoantennas have earned outstanding credits for their powerful ability to couple light from free-space into sub-wavelength-sized structures and to enhance the electric field confinement. One of the most appealing plasmonic applications is biosensing: to detect and identify many bio-information of a molecule in a single test. Consequently, surface enhanced spectroscopy in a broad infrared (IR) range is required. In this article, a barcode-like nanostructured surface of a metal-insulator-metal (MIM) platform serves as optical transducer with tunable localized surface resonances (LSPR). The conception, fabrication, and optical characterization of periodic arrays of aluminum bowties (Al-BT) within a MIM structure compatible with Si-technology are reported. LSPR positions are extended by controlling the side length of the tip-to-tip facing triangles. The reflectance measurements correlate extremely well to numerical simulations. The simulated electrical field confinement provides up to 103 of intensity relying on the tip-to-tip nanogap value. Surface-enhanced infrared absorption (SEIRA) gives simultaneously spectral information on both far-field behavior and near-field enhancement of several vibrational lines of our trial molecule (vanillin) achieved with the barcode-like Al-BT. The analysis of Fano-like profiles is concluded with SEIRA enhancement factors higher than 107 for frequency tuning ratios below 1 between the far-field plasmonic resonances and the selected vanillin IR absorption lines.