Direct Measurement of Intermolecular Bonding of Bio-Related Molecules by Terahertz Surface Plasmon Resonance

The terahertz (THz) band is a crucial electromagnetic region for intermolecular binding sensor applications. Its energy aligns with intermolecular vibration energies, allowing direct observation of specific bonding states in biomolecular systems without fluorescent molecules labeling. This study focuses on exciting surface plasmon resonance (SPR) in the THz range to observe the synergistic effects of two resonance phenomena, namely, intermolecular vibrational resonance and SPR, aiming the label-free detection of intermolecular binding. Despite previous research highlighting the excitement of SPR using topological insulators (TIs) in the THz region mainly in calculation, the experimental demonstration of label-free detection has not yet been achieved. This study successfully demonstrated the direct detection of several types of important intermolecular bindings in biomolecules, which is not possible for conventional visible light SPR, using a THz-SPR device with a Bi2Se3 grating structure. In addition, this study not only explores the mechanisms underlying the phenomenon but also discusses the limitations of current THz-SPR devices.