Opto-Thermophoretic Printing of Gold Nanosphere Assemblies with Tailorable Packing via Ligand Chain Length

The ability to control nanoparticle assembly on substrates using light offers unique opportunities for the fabrication of functional nanostructures. Herein, the opto-thermophoretic patterning of gold nanoparticles is mediated by carboxylated thiol ligands with varying chain length, revealing how ligand structure governs assembly dynamics and final morphology. Upon laser irradiation of a gold nanosphere dispersion in the presence of ω-mercaptocarboxylic acids, localized surface plasmon resonance creates a temperature gradient that promotes ligand exchange while attracting nearby particles, leading to thiol-functionalized nanoparticles that can bind to a glass substrate. Comparing short (C3), intermediate (C12), and long-chain (C16) ligands, we demonstrate that ligand length plays a critical role in nanoparticle–nanoparticle and nanoparticle–substrate interactions under nonequilibrium conditions. The criteria to pattern gold nanosphere layers with hexagonal packing symmetry was established, providing highly uniform surface-enhanced Raman scattering signal across the patterned assembly. This work provides insights into how the structure of simple aliphatic ligands impacts thermally driven nanoparticle patterning on substrates. This will broaden the scope of potential materials that can be printed by thermophoresis, opening avenues for the design of tailorable nanostructured materials.