Resonant Plasmonic–Biomolecular Chiral Interactions in the Far-Ultraviolet: Enantiomeric Discrimination of sub-10 nm Amino Acid Films

Resonant plasmonic–molecular chiral interactions
are a promising
route to enhanced biosensing. However, biomolecular optical activity
primarily exists in the far-ultraviolet regime, posing significant
challenges for spectral overlap with current nano-optical platforms.
We demonstrate experimentally and computationally the enhanced chiral
sensing of a resonant plasmonic–biomolecular system operating
in the far-UV. We develop a full-wave model of biomolecular films
on Al gammadion arrays using experimentally derived chirality parameters.
Our calculations show that detectable enhancements in the chiroptical
signals from small amounts of biomolecules are possible only when
tight spectral overlap exists between the plasmonic and biomolecular
chiral responses. We support this conclusion experimentally by using
Al gammadion arrays to enantiomerically discriminate ultrathin (<10
nm thick) films of tyrosine. Notably, the chiroptical signals of the
bare films were within instrumental noise. Our results demonstrate
the importance of using far-UV active metasurfaces for enhancing natural
optical activity.