Enantiomeric and protein structural sensing via high-Q all-dielectric metasurfaces

Spectroscopic analysis of biomolecules is vital in diagnostics and pathogen detection, yet the nanoscale dimensions of chiral molecules make light–matter coupling extremely weak. Here, we present an all-dielectric achiral metasurface of air-microcavity cubes that generates strongly superchiral near fields for highly sensitive molecular detection. The structure supports two resonant modes: a low-Q mode 1 with peak and microcavity-averaged superchirality factors of 15 and 6, respectively, and a high-Q mode 2 with corresponding values reaching 110 and 62. Near-infrared circular dichroism (CD) detection of D- and L-tryptophan is demonstrated, with equal-magnitude and opposite-sign responses enabling enantiomeric-excess analysis. Experimentally, the observable CD signal is predominantly governed by the more robust low-Q mode 1 mainly due to the stronger spatial overlap between the molecular adsorption regions and the corresponding superchiral hotspots, whereas mode 2 provides the upper theoretical enhancement limit of ∼250-fold. The same platform discriminates protein secondary structures with varying α-helix and β-sheet fractions under picogram-level surface adsorption, where isotropic and anisotropic molecular polarizability models account for the observed spectral differences. The proposed all-dielectric achiral metasurface offers low loss, low background noise, and high sensitivity, providing a promising route for chiral molecule detection.