Thermo-Responsive Surface Potential Modulation in Gold Nanoparticles Modified With Oligo(ethylene glycol) Derivatives

Smart materials that alter their physical properties in response to external stimuli have attracted significant interest for a wide range of applications. Among them, temperature-responsive materials operating near physiological temperatures are particularly promising for biomedical uses. Such materials are generally understood to undergo hydration-dehydration transitions upon temperature changes, leading to reversible switching between hydrophilic and hydrophobic states. While hydrophobic interactions play a central role in biological systems, the temperature-dependent behavior of surface charge has remained largely unexplored. Here, we investigate the surface charge properties of temperature-responsive gold nanoparticles coated with oligo(ethylene glycol) (OEG)-based ligands. Despite the absence of intrinsic charged groups, these nanoparticles exhibit negative zeta potentials in neutral to alkaline environments. Notably, increasing temperature induces not only a hydrophilic-to-hydrophobic transition but also a concomitant increase in surface potential. The results suggest that hydroxide ions are adsorbed at lower temperatures and desorbed upon heating in association with ligand dehydration. This coupled transition provides new insight into dynamic regulation of nanomaterial interfacial properties and may enable stimulus-responsive control of interactions in biological environments.