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.