Advances in terahertz biosensors toward photon-molecule interplay

To comprehend biological processes for healthcare, environmental, food, and security applications, establishing sensitive, reliable, and rapid techniques for detecting biomolecular substances is essential. However, conventional labeling methods suffer from reliability and reproducibility issues because they influence the experimental outcomes. Therefore, a label-free biomolecular sensing technique is required to overcome these limitations. From this perspective, terahertz label-free biomolecular sensing techniques have attracted significant attention owing to their unique characteristics of low photon energy and ability to probe overall dielectric responses and low-frequency vibrational modes from intermolecular interactions. In this review, we first present the distinctive characteristics of terahertz waves for detecting molecules and biological samples through a comparison with conventional biomolecular sensing techniques and vibrational spectroscopy. Then, the challenges and opportunities in the latest technologies of metasurface-based terahertz biomolecular detection are introduced, spanning from conventional strategies for enhanced terahertz absorption cross-sections to emerging frontiers exploring terahertz chirality and strongly coupled polaritons.