Molecular Chiral Response Enhanced by Crosstalking Quasi-Bound States in the Continuum

TL;DR

This paper demonstrates that dielectric metasurfaces leveraging crosstalk between quasi-bound states in the continuum can significantly enhance chiral optical responses, enabling ultrasensitive detection of molecular handedness at very low concentrations.

Contribution

It introduces a novel dielectric metasurface design that amplifies modal crosstalk to boost chiroptical signals beyond traditional local field enhancement methods.

Findings

Differential transmittance up to 1% for small Pasteur parameters.

Supports detection of molecular chirality at low concentrations.

Enhances nanophotonic chiral sensing capabilities.

Abstract

Identifying the handedness of chiral molecules is of fundamental importance in chemistry, biology, pharmacy, and medicine. Nanophotonic structures allow us to control light at the nanoscale and offer powerful tools for chiral sensing, enabling the detection of small analyte volumes and low molecular concentrations by harnessing optical resonances. Most existing strategies rely on intuitive concepts such as strong local field enhancement or large local optical chirality, often achieved by engineering electric and magnetic Mie resonances in dielectric or plasmonic nanostructures. Recent insights, however, reveal that the chiroptical response of resonant systems is governed not only by local field effects, but also by less obvious mechanisms such as modal crosstalk. In this work, we present a dielectric metasurface engineered to amplify the modal crosstalk by supporting two nearly degenerate, high-quality-factor resonant states known as quasi-bound states in the continuum. Our theoretical and numerical analysis predicts a pronounced differential transmittance that exceeds the detection threshold of standard spectrometers. In particular, the differential transmittance reaches up to $10^{-2}$ for the Pasteur parameter $\kappa = 1\cdot10^{-4}$. These findings advance the capabilities of nanophotonic sensors for chiral detection, paving the way toward ultrasensitive identification of molecular handedness in increasingly smaller volumes and concentrations at the experimentally visible level.