  In the close vicinity of a chiral nanostructure, the circular dichroism of a
biomolecule could be greatly enhanced, due to the interaction with the local
superchiral fields. Modest enhancement of optical activity using a planar
metamaterial, with some chiral properties, and achiral nanoparticles has been
previously reported. A more substantial chirality enhancement can be achieved
in the local filed of a chiral nanostructure with a three-dimensional
arrangement. Using an embossed chiral nanostructure designed for chiroptical
sensing, we measure the circular dichroism spectra of two biomolecules,
Chlorophylls A and B, at the molecular level, using a simple polarization
resolved reflection measurement. This experiment is the first realization of
the on-resonance surface-enhanced circular dichroism, achieved by matching the
chiral resonances of a strongly chiral metamaterial with that of a chiral
molecule, resulting in an unprecedentedly large differential CD spectrum from a
monolayer of a chiral material.
