Deciphering Aggregation-Induced Tunable Circular Dichroism of AuBP@Ag and AuBP@Au Chiral Core-Shell Plasmonic Nanoparticles

Plasmonic nanoparticles exhibiting strong and tunable chiroptical signals have been drawing much interest recently due to their potential vast applications. A few years ago, it was shown that seed-mediated metal growth can be harnessed to make single nanoparticles intrinsically chiral. Such structures typically manifest strong circular dichroism spectral features that can be further tuned by pure colloidal aggregation, as shown by recent experiments on chiral AuBP@Au and AuBP@Ag core-shell bipyramids. Nevertheless, the origin of such effects, either CD suppression or the rise of new CD bands upon aggregation, has remained obscure. Here, by combining theoretical modeling and experiments, we shed light on such phenomenon, disclosing that single-particle chirality drives the formation of either chiral or achiral aggregates depending on the shape and metal composition of the outer shell, thereby suggesting further avenues to tailor chirality at the nanoscale.