Experimental observation of giant chiroptical amplification of small chiral molecules by gold nanosphere clusters

We have experimentally observed around 2 orders of magnitude circular dichroism (CD) enhancement in the visible region for cysteine molecules located in the hotspots of gold nanosphere clusters. The observed plasmon-induced CD responses show a significant correlation with the chiral nature of molecules at the hotspots. These results provide a concrete experimental demonstration on the predicted chiroptical transfer and amplification effect that arises from hotspot-mediated exciton-plasmon interactions in a strongly coupled metallic nanostructure, even though the exciton-plasmon coupling works at a far off-resonant regime. Our findings suggest here that plasmonic hotspot-based CD amplifier may provide a new strategy for ultrasensitive detection and quantification of molecular chirality-a key aspect for various bioscience and biomedicine applications.