Uncovering Origin of Chirality of Gold Nanoparticles Prepared through the Conventional Citrate Reduction Method.

Chiral nanoparticles are one of the research hotspots in the field of materials science, chemistry, and biology. Understanding and controlling the chirality of nanoparticles is one key step toward their use, but the origin of nanoparticles' chirality and its determinative factor are not well understood. In this work, we studied the chirality of gold nanoparticles (AuNPs) prepared through the conventional citrate reduction method. Unexpectedly, it was found that small AuNPs (∼13 nm) exhibited opposite chirality to the large AuNPs (>30 nm). The origin of the AuNPs chirality was revealed by comparing the crystal structure between small AuNPs and large AuNPs. It was proposed that the lattice orientation of fivefold-twinned AuNPs may be responsible for the intrinsic chirality of AuNPs. This work provides a deep mechanistic understanding of the intrinsic chirality of the AuNPs and will boost the development of the structure-controlled synthesis and application of chiral AuNPs and other chiral nanomaterials. Furthermore, based on the unexpected size effect, chiral AuNP probes were rationally constructed to improve the precision of chiral recognition.