Thermal-induced growth of gold nanoparticles conjugated with thermoresponsive polymer without chemical reduction

The growth of gold nanoparticles without chemical reduction of gold (III) ions was achieved by the disruption of thermoresponsive polymers conjugated with the gold nanoparticles through the phase transition of the polymers. When a solution of gold nanoparticles coated with thermoresponsive polymers was heated, chains of the thermoresponsive polymers were disrupted because of dehydration, resulting in the fusion of gold nanoparticles to form larger nanoparticles. The evolution of the extinction band around 550 nm evidenced the formation of these large (post-fusion) gold nanoparticles, which were characterized by transmission electron microscope (TEM) and dynamic light scattering (DLS). TEM images verified the formation of the large gold nanoparticles having particle sizes of 80-100 nm, whereas DLS indicated the existence of large nanoparticles with hydrodynamic diameters exceeding 200 nm. The deposition did not require the addition of reductants or trivalent gold ions for the formation of the large gold nanoparticles. Both the heating and the solution conditions were studied to elucidate the mechanism of the formation of large gold nanoparticles.