Thermo- and pH-Responsive Hydrogel-Coated Gold Nanoparticles

This article describes the structural and optical properties of a new class of hybrid nanoparticles that consists of a small gold core (∼60 nm in diameter) coated with a biocompatible hydrogel polymer shell varying from ∼20 to ∼90 nm in thickness. These nanoparticles are being developed to serve as unique drug-delivery vehicles that have the ability to respond to ambient changes in pH and/or temperature. A particularly attractive feature of these nanoparticles derives from the fact that the hydrogel can be thermally activated by exposure to light via exploitation of the strong plasmon absorption of the gold nanoparticle core. The hydrogel coating consists of a known biocompatible thermo-responsive copolymer derived from the radical polymerization of a selected mixture of N -isoproprylacrylamide and acrylic acid. The morphology and elemental composition of the composite nanoparticles were characterized by field emission scanning electron microscopy and energy-dispersive X-ray scattering, respectively. The optical properties of the nanoparticles were analyzed by UV spectroscopy, and the average particle size was evaluated as a function of temperature and/or pH using dynamic light scattering. The results demonstrate not only that these new hybrid nanoparticles can be reliably prepared through the surfactant-free emulsion polymerization but also that their responses to external stimuli are completely consistent with the targeted drug-delivery objectives.