Nanophotonics
can boost the weak circular dichroism of
chiral molecules.
One mechanism for enhanced chiral sensing relies on using a resonator
to create fields with high optical chirality at the molecular position.
Here, we elucidate how the reverse interaction between molecules and
the resonator, called chirality transfer, can produce stronger circular
dichroism. The chiral analyte modifies the electric and magnetic dipole
moments of the resonator, imprinting a chiral response on an otherwise
achiral resonance. We demonstrate that silicon nanoparticles and metasurfaces
tailored for chirality transfer generate chiroptical signals orders
of magnitude higher than the contribution from optical chirality alone.
We derive closed-form equations for the dependence of chirality transfer
on molecular chirality, molecule–resonator distance, and Mie
coefficients. We propose a dielectric metasurface for a 900-fold circular
dichroism enhancement on the basis of these principles. Finally, we
identify a fundamental limit to chirality transfer. Our findings thus
establish key concepts for nanophotonic chiral sensing.