Polarization-Dependent Dual-Mode Surface Enhanced Infrared Absorption Laser Spectroscopy

Broadband tunable mid-infrared laser absorption spectroscopy is an in-situ analytical tool that holds promising prospects in the detection of complex analytes. It can provide structural and chemical information of molecules residing in samples or at the surfaces of samples through transmission or reflection mode correspondingly. We proposed polarization-dependent dual-mode surface enhanced infrared absorption (SEIRA) laser spectroscopy for the first time, which allows seamlessly switching between transmission and reflection modes. A new design of a six-pointed asterisk nanoantenna chip is incorporated to enhance the signal with elevated design freedom in terms of polarization-dependent resonance. The new chip has achieved the most uniform resonance coverage to our knowledge, over a bandwidth of 390 cm-1 across five main fingerprints of alanine. Our dual-mode SEIRA laser spectroscopy serves as an effective approach to detect broadband and densely-packed fingerprints, allowing comprehensive analysis of biomolecules.