Optical sorting of sub-10 nm chiral entities using non-chiral metasurface

Enantioseparation is a fundamental problem in pharmaceutics and agrochemicals. Yet, the prevailing chemical techniques are not effective. In this paper, we proposed an achiral metasurface, which consists of a disk-double split ring (DDSR) resonator sustaining dipole-octupole (DO) Fano resonance (FR). We have proved that such a resonance can significantly enlarge the chiral gradient force of the enantiomers by numerical simulation. We find that the resonator has a large chirality density gradient near the DO-FR, which strengthens the chiral gradient force that can discriminate the sub-10 nm chiral nanoparticles. Therefore, the enantioselective optical potential can trap or push different enantiomers. We propose a method to enhance the chiral gradient force by using an achiral metasurface consisting of a disk and an asymmetric double split-ring resonator, which can promote the development of enantiomer purification and separation technology, and bring new prospects for the latest all-optical enantiomer synthesis technology.