Moiré metasurfaces with tunable near-infrared-I chiroptical responses for biomolecular chirality discrimination†

Manipulating circular dichroism in chiral metasurfaces has been increasingly important for a wide range of polarization-sensitive photonic applications. However, simple methods for presenting chiral nanostructures with tunable and considerable chiroptical responses in the near-infrared-I regime remains underexplored. Herein, two sheets of suspended symmetric bilayer metagratings fabricated via single-step electron beam lithography are stacked into a moiré metasurface with its circular dichroism value reaching up to 20.9°. The chirality of the moiré metasurface can be fully tuned in terms of both its sign and magnitude by adjusting the in-plane angle between the two twisted sheets of metagratings. The multilayered design is accessible to the coupling of hybridized plasmons for governing the chiroptical properties in the near-infrared-I regime. The ratio between the resonance wavelength and the grating period is about 1.65, which is much lower compared to that in most existing moiré metasurfaces with strong chiroptical responses. Furthermore, the superchiral fields in the inter-sheet region are further exploited for label-free enantiodiscrimination with ultrahigh sensitivity of 10.17 nm fmol⁻¹ mm². The proposed moiré metasurfaces with strong near-infrared-I chirality hold great potential for supporting polarization engineering and biomolecular detection, paving a way for advanced applications in medical diagnosis, biomedical imaging, and display technologies.