The intriguing role of L-cysteine on the modulation of chiroplasmonic properties of chiral gold nano-arrows

Developing chiral plasmonic nanostructures represents a significant scientific challenge due to their multidisciplinary potential. Observations have revealed that the dichroic behavior of metal plasmons changes when chiral molecules are present in the system, offering promising applications in various fields such as nano-optics, asymmetricwe explored the synthesis of plasmonic gold nanoparticles and the role of cysteine on their chiroplasmonic properties. Specifically, we synthesized chiral gold nano-arrows using seed-mediated-growth synthesis method, in which gold nanorods are used as seeds while incorporating L-cysteine (L-cys) into growth solution as a chiral ligand. Our results show clearly that the chiral molecule transfers chirality to gold nanocrystals and the morphology is controlled through kinetic growth. In addition, we demonstrate that the chiroplasmonic properties, such as the sign of circular dichroism, can be modulated using only one of enantiomeric form in the growth solution. To understand the origin such effect, we conducted theoretical modelling using density functional theory. Our results point to the intermolecular cysteine interactions as a key factor in the dichroic properties of surface-molecule chiral systems.