Gold nanoparticles (AuNPs) have been studied extensively owing to their distinctive physicochemical properties and broad applications in catalysis, sensing and biomedicine. Focussing on catalysis, their unique potential becomes particularly pronounced when their dimensions fall below approximately 5 nm, where they enter a fundamentally different size regime. At this scale, their behaviour diverges not only from bulk gold but also from larger (10–100 nm) nanostructures.
In the sub-5 nm regime, the predominance of surface atoms means that reactivity and thermodynamic stability can be dominated by ligand interactions. Furthermore, ultrasmall particles frequently deviate from bulk crystallographic symmetry, adopting reconstructed or non-crystalline motifs that can give rise to emergent chiral behaviour. Together, these characteristics create opportunities to exploit size-dependent phenomena for catalytic control.
This work examines synthetic and stabilisation strategies for aqueous-phase sub-5 nm AuNPs functionalised with carboxylate- and thiol-containing ligands. By integrating high-resolution electron microscopy with computational modelling, we investigate growth pathways, structural evolution and stability controls. Systematic variation of pH, ligand identity and concentration reveals that nanoparticle size and morphology are highly sensitive to solution chemistry, with pre-nucleation clusters acting as long-lived intermediates that influence subsequent growth. Simulations (molecular dynamics and density functional theory) provide insight into ligand-mediated stabilisation and indicate size-dependent chirality.
Taken together, these findings advance understanding of particle–ligand interactions at the smallest accessible nanoscale dimensions. They demonstrate how precise synthetic control, coupled with molecular-level modelling, can establish rational design principles for tailoring nanoparticle structure and functionality. Such insights lay the groundwork for engineering gold nanomaterials whose catalytic performance can be systematically tuned through size control.
Acknowledgment: The presenter acknowledges a Royal Society Wolfson Fellowship (RSWF\R2\192007) and the work of doctoral students Pak Leung Aidan Yiu and Henry Gauder.
