Chapter 2. Synthesis of Poly(<i>N</i>-isopropylacrylamide) Microgel Particles Containing Gold Nanoshell Cores with Potential for Triggered De-swelling

Abstract

This work describes the synthesis of gold nanoshells (silica core–gold shell) coated with a thermo-responsive and biocompatible poly(N-isopropylacrylamide) hydrogel layer. The negatively charged silica cores were functionalised with poly(diallyldimethylammonium chloride), making them cationic. Successively, small negatively charged gold colloid particles were adsorbed onto their surface, by electrostatic attraction, as nucleation sites; finally, further reduction (sonication assisted) of gold onto the silica involved the coalescence of the gold particles into a complete gold shell. Such particles show interesting photo-thermal properties in that when irradiated with near-infrared radiation they heat up.The encapsulation of the gold nanoshells within the hydrogel over-layer was carried out via surfactant-free emulsion polymerisation of N-isopropylacrylamide. Reversible volume changes of the composite hydrogel nanoparticles were observed as a function of the temperature, with a lower critical solution temperature around 35 °C, similar to that of the pure N-isopropylacrylamide particles.