The intriguing role of L-cysteine in 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, asymmetric catalysis, polarization-sensitive photochemistry and molecular detection. In this study, we explored the synthesis of plasmonic gold nanoparticles and the role of cysteine in their chiroplasmonic properties. Specifically, we synthesized chiral gold nano-arrows using a seed-mediated-growth synthesis method, in which gold nanorods are used as seeds while incorporating L-cysteine 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 enantiomeric form in the growth solution. To understand the origin of such an 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.