Terahertz sensing based on plasmonic metastructures

Terahertz (THz) waves resonate with the rotational and vibrational modes of many complex molecules, offering great potential for applications in biological, medical, and security sensing. However, their practical implementation is hindered by the intrinsic size mismatch between the long THz wavelengths and the much smaller dimensions of target analytes. Metastructures supporting spoof surface plasmon polaritons (SPPs) provide an effective solution by confining THz waves to deeply subwavelength scales. The resulting spoof SPPs enable strong electromagnetic field localization and pronounced near-field enhancement, thereby amplifying light-matter interactions and improving sensing sensitivity. In this review, we first introduce the fundamental principles of THz sensing based on plasmonic metastructures, followed by a discussion of recent advances in systems exploiting propagating spoof SPPs, localized spoof SPPs, and hybrid modes arising from their coupling, as well as other emerging mechanisms. We conclude with perspectives on future opportunities and challenges for THz sensing technologies empowered by spoof SPPs.