Microwave, photo- and thermally responsive PNIPAm-gold nanoparticle microgels.

Microwave-, photo- and thermo-responsive polymer microgels that range in size from 500 to 800 microm and are swollen with water were prepared by a novel microarray technique. We used a liquid-liquid dispersion technique in a system of three immiscible liquids to prepare hybrid PNIPAm- co-AM core-shell capsules loaded with AuNPs. The spontaneous encapsulation is a result of the formation of double oil-in-water-in-oil (o/w/o) emulsion. It is facilitated by adjusting the balance of the interfacial tensions between the aqueous phase (in which a water-soluble drug may be dissolved), the monomer phase and the continuous phase. The water-in-oil (w/o) droplets containing 26 wt% NIPAm and Am monomers, 0.1 wt% Tween-80 surfactant, FITC fluorescent dye and colloidal gold nanoparticles spontaneously developed a core-shell morphology that was fixed by in situ photopolymerization. The results demonstrate new reversibly swelling and deswelling AuNP/PNIPAm hybrid core-shell microcapsules and microgels that can be actuated by visible light and/or microwave radiation (<or=1,250 nm) and/or temperature. This is the first study to demonstrate that incorporating AuNPs speeds up the response kinetics of PNIPAm, and hence enhances the sensitivity to external stimuli of PNIPAm. These microgels can have potential applications for microfluidic switches or microactuators, photosensors, and various nanomedicine applications in controlled delivery and release.