ETD/MTD-Degenerate Metasurface for Highly Sensitive Terahertz Circular Dichroism Detection

Terahertz circular dichroism (TCD) spectroscopy holds great potential for chiral sensing of biomolecules but has been limited by insufficient detection sensitivity. Enhancing optical chirality in the near field through microstructures is critical for improving chiral detection sensitivity. Here, we propose an approach for highly sensitive narrowband TCD detection by generating uniform and accessible superchiral near-fields using an ETD/MTD-degenerate metasurface that supports degenerate resonances of both electric toroidal dipole (ETD) and magnetic toroidal dipole (MTD). Under circular polarization (CP) incidence, this design enhances the local maximum and average optical chirality within the sample solution-filled region near 0.26 THz by more than 631× and 80×, respectively, thereby achieving a over 80-fold enhancement of the TCD signal. Our results pave the way for ultrasensitive TCD detection of trace biomolecules.