Light-to-matter chirality transfer in plasmonics

Plasmonic nanostructures are important tools in the study of chirality in the nanoscale. They are systems composed of conducting materials that support resonant excitations of the oscillatory motion of their conduction electrons. Exciting these plasmonic modes effectively localizes radiant energy in and around these nanostructures, which act as electromagnetic antennas operating in the UV-to-IR spectral range. Plasmonic systems can enhance the chiroptical activity of chiral molecules in near-field interaction with them, affording improved sensing capabilities at low analyte concentration or in samples with a low enantiomeric excess. They have also become an important platform through which to test and develop artificial materials with exceptionally large chiroptical activity, through the creation of plasmonic structures or assemblies with chiral geometries or arrangements. The fabrication of chiral plasmonic nanostructures employs a variety of techniques, the most common including the introduction of chiral asymmetry through top-down designs or introducing chiral molecules to direct the chiral growth of the structure. Recently, a different approach is being explored, which involves using chiral light as the only source of asymmetry in developing chiral plasmonic nanostructures. Chirality in this case arises from local transformations occurring on the surface or environment of the nanostructure, in a pattern that follows the local, chiral pattern of excitation induced by the impinging light. This article introduces and explores light-to-matter chirality transfer in plasmonics, contextualizes it within an introductory overview of light-matter interaction and chirality, reviews examples of this nascent technique and discusses its potential in exploiting different energy-transfer mechanisms supported by plasmonic nanostructures.