Near-Field Topology-Optimized Superchiral Metasurfaces for Enhanced Chiral Sensing

Abstract: The detection and discrimination of molecular chirality are essential for advancing pharmaceutical and biological applications. While nanophotonic platforms offer a route to enhance chiral light-matter interactions, existing device concepts for chiral sensing remain heuristic, resulting in limited chiral enhancement and control over chiral hotspot placement within nanostructures. Here, we introduce an inverse-design framework that directly optimizes superchiral near fields in photonic nanostructures and demonstrate its powerful opportunities for enantioselective analysis. We first show that freeform achiral metasurfaces can be optimized to achieve an 800-fold chiral density enhancement, with fully customizable chiral hotspot placement for direct molecular interaction. We further demonstrate ultrasensitive detection of chiral analytes and achieve a 116-fold increase in detection sensitivity over the native enantiomeric response. Lastly, we extend our platform to determine chiral-molecule concentration and resolve enantiomeric excess in chiral mixtures. Our framework offers a generic route to enabling nanophotonic platforms for detecting chiral compounds and can be integrated with a broad range of spin-based photonic materials for applications in valleytronics, chiral emission control, and topological photonics.