Nanophotonic chiral sensing: From principles to practice

Nanophotonic chiral sensing enables the characterization of the optical activity of chiral molecules, even at ultralow concentrations, whereas conventional chiroptical spectroscopy is limited to bulk measurements requiring high concentrations. This review provides a comprehensive overview of nanophotonic chiral sensing, covering fundamental principles to practical experimental considerations. We first introduce the theoretical framework of chiral light-matter interactions, including the electromagnetic description of chiral molecules and the chiral structures of light. Discussion on the chiral structure of light encompasses spin angular momentum, optical helicity, optical chirality, and zilches. We then review various chiral sensing mechanisms, such as single-molecule circular dichroism enhancement, nanophotonically induced circular dichroism in sensor-molecule complexes, chiral spectral shifts, molecule-nanostructure Coulomb interactions, and the chiral Purcell effect, along with their experimental implementations. We also present guidance on chiroptical spectroscopy instrumentation, covering both conventional and emerging techniques. Finally, we provide our perspectives on future research directions in nanophotonic chiral sensing. We hope that this review will inspire further advancements in precise chiral sensing beyond current detection limits.