Functionally multiplexed sensor based on separated bilayer metasurface for enhanced terahertz sensing

Abstract

Terahertz (THz) metamaterials can confine electric field energy to subwavelength regions, thereby significantly enhancing light-matter interactions. Consequently, they hold broad application prospects in the field of biochemical sensing. However, traditional metamaterials generally suffer from low spatial overlap between the analyte and the localized electric field, as well as limited detection functionality. This paper proposes a metal–polymer separated bilayer metasurface structure that synergistically achieves high-sensitivity refractive index sensing and molecular fingerprint detection by enhancing spatial overlap. Specifically, this structure establishes a dual-mode resonance mechanism by introducing in-plane symmetry breaking and a separated bilayer design: In the high-frequency region, the excited high-Q quasi-bound state in the continuum (q-BIC) resonance greatly enhances the localized electric field, enabling a highly sensitive response to refractive index variations. More importantly, in the low-frequency region, the broad dipole resonance allows for the identification of characteristic molecular absorptions, thereby enabling molecular fingerprint detection. The results demonstrate that the proposed structure effectively enhances the interaction between THz waves and analytes, achieving a q-BIC resonance sensitivity of 0.541 THz RIU−1. Moreover, the signal corresponding to the characteristic absorption peak of lactose molecules is amplified by up to 18 times, thereby achieving functional multiplexing of refractive index sensing and molecular fingerprint detection within a single device. This work provides a new strategy for applying THz sensors to trace analyte detection.