Unraveling the complex interactions between plasmonic Ag nanoparticles and biomolecules for enhancing molecular chirality

Plasmonic nanostructures have been widely employed to enhance the chiral light-matter interactions for chirality sensing owing to their intriguing optical properties. However, a quantitative understanding of the correlation between enhanced molecular chirality and plasmonic properties in plasmonic nanoparticle-molecule complexes remains a challenge yet to be addressed. Here we demonstrate the complex interactions between Ag nanoparticles and biomolecules that generate distinct plasmonic circular dichroism signals ranging from UV to visible wavelengths. By deliberately changing the surface coverage of chiral molecules, the geometry of Ag nanoparticles, and the aggregation states of the complexes, three distinct underlying mechanisms were found to be intertwined and hybridized for enhancing circular dichroism signals. We further employed the chiral plasmonic nano-particle-molecule complexes to quantify the enantiomeric purity of cysteine and explore their possible applications in other chiral molecules. The insights gained from this work shed light on the underlying mechanisms dictating the enhanced circular dichroism signals of chiral plasmonic nanoparticle-molecule complexes.