Structural and Optical Characterization of Reaction Intermediates during Fast Chiral Nanoparticle Growth

Abstract

As nanoparticle morphologies produced by seeded growth expand in number and complexity, tracking their evolution during growth is increasingly important to achieving a mechanistic understanding. However, fast reactions such as chiral growth, in which morphologies change within seconds, remain challenging to monitor at the relevant time scale. We introduce a method based on fast addition of the reducing agent NaBH₄, enabling interruption of gold nanoparticle growth, as well as access to reaction intermediates for morphological and optical investigations. We show that NaBH₄ reduces the remaining gold salt precursors into achiral nanoparticles and prevents further evolution of the target particles, resulting in a time series with intervals down to seconds. The method is demonstrated on fast, micelle-directed, chiral growth on single-crystalline or penta-twinned nanorod seeds, showing fine variations in the temporal evolution of chirality depending on crystal habit. These series provide representative snapshots from a chirality continuum, offering a platform for studying optical-structural relationships.

Keywords: chiral descriptors; chiral nanoparticles; chiral plasmonics; circular dichroism; electron tomography; optical-structural relationship; seeded growth.