Metasurface analogues of molecular diastereomers from hierarchical multiscale chiral interactions with biomolecules.

Chirality occurs at molecular and nanoscales, but these forms of handedness are usually treated independently. We demonstrate a hybrid chiral state, termed a meta-diastereomer, in which molecular chirality and nanoscale structural chirality are coupled at an interface to determine the optical response, with distinct states defined by the relative handedness of the two components, as in molecular diastereomers. Unlike strategies that rely on enhanced near-field optical chirality, the coupling here arises from a charged, polarisable interfacial layer that perturbs electromagnetic boundary conditions. The resulting reduction in symmetry renders linear optical observables stereostructurally informative, in the same way that molecular diastereomers can be distinguished using non-chiral measurement techniques. This behaviour distinguishes native versus denatured protein layers and differentiates protein-protein binding states in a model antigen-antibody system. These results identify electromagnetic boundary conditions as a mechanism by which chirality can be transmitted across length scales and provide a boundary-condition-based framework for hierarchical chirality at biomolecule-metasurface interfaces.