Ultra-Sensitivity of Active Surface Growth: How Sub-ppm Thiol-Ligands Drive Intra-Particle Competition in Gold Nanohexagrams

We reveal an imbalanced growth regime in the synthesis of colloidal chiral gold nanostructures. Beyond the prevailing view that chiral ligands simply imprint chirality onto nanostructures formed in cetyltrimethylammonium bromide (CTAB) environment, we show that CTAB provides the background conditions for active surface growth, where cysteine (Cys) at sub-ppm concentrations act as strong-binding ligands that induce difference among the active sites: from homogeneous chiral nanohexagrams, to nanotriskelia with three elongated arms, and nanocomets with a single tail. Extending this concept to diverse thiol-based ligands (thiols), we define the critical ligand concentration (CLC) as a quantitative metric for evaluating ligand affinity to Au surfaces, revealing the critical role of amine-thiol synergy. Moreover, the imbalanced growth regime depends critically on deposition kinetics: rapid Au deposition drives a positive-feedback process that amplifies small differences in site reactivity. Together, our findings identify the thiol/CTAB ratio, ligand affinity, and deposition rate as the key parameters that govern intraparticle competition and growth-mode transitions.