Resonant chiroptical effects in an all-dielectric metasurface with monoclinic lattices for terahertz sensing applications

Over recent years, chiral metasurfaces have emerged as pivotal platforms for ultrasensitive biosensing. However, the excitation of chiroptical responses in conventional chiral metasurfaces predominantly relies on intricate asymmetric <i>meta</i>-atoms or elaborate geometric configurations. Here, we report an all-dielectric chiral metasurface consisting of an array of circular air holes in the monoclinic lattice. The proposed metasurface achieves strong intrinsic chirality by breaking in-plane mirror symmetries by optimizing side-length differences <i>δ</i> and lattice angle <i>θ</i>. Theoretical analyses of induced electromagnetic fields reveal that the observed chiroptical responses originate from spin-selective multipole excitations and localized field enhancements. Experimental validations based on the fabricated sample and terahertz characterization confirm the excitation of resonant chiral dichroism (CD) signals. Furthermore, we demonstrate the practical biosensing capabilities of the proposed chiral metasurface by detecting bovine serum albumin (BSA) samples with different concentrations, which manifests good sensing performance, including high sensitivity (0.023 (mg mL^-1)^-1) and a wide detection range (0.3-30 mg mL^-1). This work opens a new avenue for designing chiral metasurfaces with simple structures but high performance, advancing practical applications in label-free biosensing and chiral nanophotonics.