Isotropic Size Control of Chiral Gold Helicoids

Chiral nanomaterials, characterized by their nonsuperimposable mirror image structures, exhibit unique physical and chemical properties, enabling diverse applications in photonics, catalysis, and biological systems. Among these, chiral plasmonic nanostructures are particularly advantageous due to their ability to confine electromagnetic fields beyond their diffraction limit, enhancing various chiral interactions. Despite significant advances in their synthesis, the scalability and structural variety of these materials remain challenging. Here, we present a systematic methodology for synthesizing chiral plasmonic nanoparticles (432 helicoid III) with a reduced size of sub-100 nm while maintaining their chiral cubic morphology evolved by a chiral organothiol, glutathione. Using a seed-mediated colloidal growth approach, we isotropically scaled down the particle size from the archetypal 180 to 85 nm by controlling the stoichiometry during the initial growth step of octahedral seeds. These smaller helicoids retain their distinct chiral morphology and exhibit a Kuhn’s dissymmetry factor (g-factor) of around 0.01 despite their sub-100 nm size. Despite reducing the particle size to less than half, we demonstrated robust and controllable chiroptical responses through spectroscopic and numerical analyses, as well as the presence of atomic level chirality through high-resolution scanning transmission electron microscopy analysis. This strategy not only overcomes simple size-related limitations but also enhances the potential applications of chiral plasmonic nanoparticles in optical, chemical, and catalytic enantioselective systems by improving their surface-to-volume ratios and reducing photonic and electronic surface scattering.