Two Better Than One: Emerging Chirality in Twisted Gold Nanorods

Chemisorption-directed growth is the most common strategy for the synthesis of intrinsically chiral plasmonic nanoparticles. This approach relies on the use of thiolated chiral molecules, such as cysteine, which are assumed to transfer chirality by selectively adsorbing onto specific gold crystal facets during growth on preformed gold seeds. We found that chiral Au nanorods (AuNRs) synthesized using aged cysteine solutions exhibit significantly enhanced anisotropy factors compared to freshly prepared solutions, thus challenging the long-standing assumption of the key role of thiol ligands. Combining circular dichroism spectroscopy, electron tomography, and density functional theory simulations, we prove that cysteine is gradually oxidized into cystine and that this transformation is responsible for the enhanced chiroptical response. We therefore identify cystine, rather than cysteine, as the chiral inducer during AuNR chiral growth. Cystine’s ability to simultaneously coordinate two gold atoms enables a more efficient transfer of molecular chirality to the growing nanocrystal. This enhanced efficiency stems from its ability to directly fit the 3-point chirality model, thereby avoiding stochastic processes. These findings redefine the role of thiolated chiral molecules in chemisorption-directed growth and provide mechanistic insights for the rational design of more effective chirality inducers.