  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
greater than 6 orders of magnitude than is achieved with conventional chirally
sensitive spectroscopic methods based on circularly polarized light. The
optimal approach for exploiting nanophotonic platforms for chiral detection
would be to use spectroscopic methods that provide a local probe of changes in
the near field environment induced by the presence of chiral species. Here we
show that surface enhanced Raman spectroscopy (SERS) is such a local probe of
the near field environment. We have used it to achieve enantiomeric
discrimination of chiral helicoid nanoparticles deposited on left and
right-handed enantiomorphs of a chiral metafilm. Hotter electromagnetic
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 we have used SERS 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.
