Enantioselective optical trapping of chiral nanoparticles by tightly focused fractional vector beams

Enantiomers exhibit markedly different chemical properties although they have the same chemical structure. The identification and separation of enantiomers have been significant issues in biomedicine and chemistry. In this work, we proposed an optical method that selective trapping of enantiomers by using tightly focused fractional vector beams (FVBs). In our proposed model, such a focused beam forms multiple local optical chirality densities (OCDs) with opposite signs at the focal plane. We found that focused FVBs can stably trap the enantiomers at the local positions with the minimum or maximum OCD according to the handedness of enantiomers. The positions and numbers of the trapped enantiomers have a relationship with the fractional topological charge. These results indicate that tightly focused FVBs are an all-optical method capable of dynamic modulation and achieving precise and stable trapping of multiple pairs of enantiomers. Our findings have practical applications in the multi-throughput and multi-sample manipulation of chiral materials.