Multiresponsive hybrid colloids based on gold nanorods and poly(NIPAM-co-allylacetic acid) microgels: temperature- and pH-tunable plasmon resonance.

This work describes the control and manipulation of the optical properties of multiresponsive organic/inorganic hybrid colloids, which consist of thermo-responsive poly-(NIPAM-co-allylacetic acid) microgel cores and gold nanorods assembled on their surface. These composites are multifunctional, in the sense that they combine the interesting optical properties of the rod-shaped gold particles--exhibiting two well-differentiated plasmon modes--with the sensitivity of the copolymer microgel toward external stimuli, such as temperature or solution pH. It is shown that the collapse of the microgel core, induced by changes in either temperature or pH, enhances the electronic interactions between the gold nanorods on the gel surface, as a result of the subsequent increase of the packing density arising from the surface decrease of the collapsed microgel. Above a certain nanorod density, such interactions lead to remarkable red-shifts of the longitudinal plasmon resonance.