Surfactant-Dominated Chirality Transfer from Asymmetric Molecules to Branched Au Nanocrystals

Chiral gold (Au) nanostructures are typically synthesized via the addition of growth seeds to reaction solutions containing Au precursors, surfactants, and enantiomeric molecules, and the geometric chirality of these nanostructures arises from enantiomer-induced asymmetric growth. However, the influence of coexisting nonchiral surfactants in reaction solutions on the chirality evolution of nanomaterials is rarely discussed. Herein, taking cysteine and hexadecyl trimethylammonium bromide (CTAB) as examples of enantiomeric molecule and surfactant, respectively, the Au reaction solution related to the growth of chiral Au nanostructures was studied in depth. Our findings reveal that increasing concentrations of cysteine promote the formation of branched Au nanostructures. With only micromolar cysteine, it is sufficient to induce the anisotropic branched growth. Nevertheless, when the reaction rates are rapid, the impacts of cysteine on branched growth are weakened. Fortunately, CTAB with the optimal concentration (1.0 mM) serves a reaction modulator, slowing asymmetric growth while enhancing the geometric chirality features of those branched Au nanostructures. When CTAB concentrations surpass 10.0 mM, the products are mainly characterized with the assembled architectures, which detrimentally affect the chirality characteristics. This work is crucial to reveal the chirality evolution mechanism of chiral nanomaterials, remarkably guiding the mediated synthesis of unprecedent chiral nanomaterials on emerging substrates.