Chiral Metafilms and Surface Enhanced Raman Scattering for Enantiomeric Discrimination of Helicoid Nanoparticles

Abstract

Chiral nanophotonic platforms provide a means of creating near fields with both enhanced asymmetric properties and intensities. They can be exploited for optical measurements that allow enantiomeric discrimination at detection levels > 6 orders of magnitude than is achieved with conventional chirally sensitive spectroscopic methods based on circularly polarized light. Here it is shown that surface enhanced Raman spectroscopy (SERS) is such a local probe of the near field environment. It is used to achieve enantiomeric discrimination of chiral helicoid nanoparticles deposited on left- and righthanded enantiomorphs of a chiral metafilm using an achiral molecule as a probe. “Hotter” electromagnetic (EM) hotspots are created for matched combinations of helicoid and metafilms (left-left and right-right), while mismatched combinations leads to significantly “cooler” electromagnetic hotspots. This large enantiomeric dependency on hotspot intensity is readily detected using SERS with the aid of an achiral Raman reporter molecule. In effect SERS is used to distinguish between the different EM environments of the plasmonic diastereomers produced by mixing chiral nanoparticles and metafilms. The work demonstrates that by combining chiral nanophotonic platforms with established SERS strategies new avenues in ultrasensitive chiral detection can be opened.