Discrete thermally responsive hydrogel-coated gold nanoparticles for use as drug-delivery vehicles

This report describes the development of optically responsive gold nanoparticles (similar to 60 nm in diameter) coated with a thermally responsive biocompatible hydrogel overlayer (20-90 nm thick). The hydrogel consists of a mixture of N-isoproprylacrylamide and acrylic acid; this copolymer can be tailored to exhibit a lower critical solution temperature (LCST) slightly above physiological temperature. When the temperature is raised above the LCST, the hydrogel polymer shrinks dramatically; in contrast, when the temperature is lowered below the LCST, the hydrogel expands to a fully swollen structure. These hybrid nanoparticles were designed for the purpose of developing an optically modulated drug-delivery system that responds to ambient changes in temperature. Specifically, drug-impregnated hydrogel coatings can be photothermally activated by exposure to light that can be absorbed by the plasmon resonance of the gold nanoparticle cores. The studies described here demonstrate that these new hybrid core-shell nanoparticles can be reproducibly prepared by surfactant-free emulsion polymerization (SFEP) and that their structural responses to external stimuli are consistent with our objective of photothermal drug delivery.