Thermo-, pH-, and light-responsive poly(N-isopropylacrylamide-co-methacrylic acid)--Au hybrid microgels prepared by the in situ reduction method based on Au-thiol chemistry.

In recent years, it has been an attractive challenge to fabricate multiple stimuli-responsive hybrid microgels composed of polymer microgel and gold nanoparticle (AuNP). Herein, we report on the detailed synthesis of poly(N-isopropylacrylamide-co-methacrylic acid)--Au hybrid microgels by in situ reduction of gold precursor in the presence of thiol-functionalized poly(N-isopropylacrylamide-co-methacrylic acid) microgels. The as-synthesized hybrid microgels showed well-defined swelling/deswelling transition in response to the surrounding temperature, pH, and light irradiation. The hybrid microgels had a unique microstructure where a large number of AuNP's distribute mainly in the interior of microgel with a fluff-like surface. The plasmonic property of the hybrid microgels can be modulated through the volume phase transition induced by the external triggers such as temperature and pH. In the reduction of 4-nitrophenol catalyzed by the hybrid microgels, it was found that the reaction rate did not increase monotonously with temperature but greatly decreased in a certain temperature range, showing a tunable catalytic activity.