ERI: Tailoring of superchiral near-fields in topology-optimized metasurfaces for enhanced chiral sensing

Non-technical Description: "Chirality" refers to objects that cannot be superimposed onto their mirror image. At the molecular scale, spatial asymmetry in mirror-image molecules, known as enantiomers, gives rise to distinct biological, chemical and pharmacological properties. In a chiral mixture, enantiomers are typically identified based on chiral optical effects; however, the differential signals between enantiomers of opposite handedness are inherently weak. While nanophotonic platforms, such as metasurfaces, can enhance light–matter interactions, it remains a challenge to achieve strong chiral response in these media through nanostructure engineering. The overarching goal of this research is to develop a photonic optimization framework for freeform metasurfaces in which strong chiral near-fields can be created at specific molecular positions. This will enable enhanced chiral fields for direct interaction with analytes, thereby advancing chiral sensing and imaging with ultrahigh sensitivity. This framework will explore the limits of nanophotonic chiral sensing, uncover the underlying electrodynamic mechanisms, and develop prototypes of ultrasensitive sensors for enantioselective analysis. In addition, the proposed project will promote the adoption of open-source software packages and provide training opportunities for undergraduate students pursuing STEM careers. Technical Description: The research aims to optimize optical chirality in freeform metasurfaces through the development of a near-field topology optimization framework. This approach provides a direct pathway to enhancing chiral near-fields and customizing their spatial distributions in nanostructured media, allowing for direct overlap with analytes for enhanced chiral sensing. The specific goals are centered around three main thrusts: (1) exploring chiral enhancement limits in resonant metasurfaces, (2) studying chirality transfer dynamics between molecules and resonators, and (3) developing prototypes of nanophotonic sensors for enantioselective analysis. The project encompassing theory, design, and experiment offers a comprehensive workflow for developing ultrasensitive chiral sensing platforms. Furthermore, the project will promote the interdisciplinary adoption of photonic design tools and enhance STEM education through cutting-edge research. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.