Temperature-Modulated Reversible Clustering of Gold Nanorods Driven by Small Surface Ligands

Temperature-modulated colloidal phase of plasmonic nanoparticles is a convenient playground for resettable soft-actuators or colorimetric sensors. To render reversible clustering under temperature change, bulky ligands are required, especially if anisotropic morphologies are of interest. This study showcases thermoresponsive gold nanorods by employing small surface ligands, bis (p-sulfonatophenyl) phenyl-phosphine dihydrate dipotassium salt (BSPP) and native cationic surfactant. Temperature-dependent analysis in real-time allowed to describe the structural features (interparticle distance and cluster size) as well as thermal parameters, melting and freezing temperatures. These findings suggest that neither covalent Au-S bonds nor bulky ligands are required to obtain a robust thermoresponsive system based on anisotropic gold nanoparticles, paving the way to stimuli-responsive nanoparticles with a wide range of sizes and geometries. In thermoresponsive plasmonics, size does matter: This study presents a strategy for preparing thermosensitive gold nanorods clustering reversibly over a broad temperature range and reaching interparticle gaps as small as 1 nm in the clustered state. This enables the possibility to exploit the full promise of plasmonic coupling and the generation of dynamic hotspots.image