Au nanoparticle templated synthesis of pNIPAm nanogels

We have explored a synthetic route toward poly(N-isopropylacrylamide) (pNIPAm) nanogels by growing a pNIPAm shell onto a metal nanoparticle seed. Nuclei compatible with precipitation polymerization of thermoresponsive polymers were formed by adsorption of NH2-terminated pNIPAm on Au nanoparticles. The adsorbed pNIPAm layer, when heated above the LCST, collapses onto the Au nanoparticle surface. This polymer layer thus serves as a hydrophobic nucleus for growing pNIPAm oligoradicals during polymer synthesis, resulting in the formation of a pNIPAm shell. Etching of the Au core from the polymer-coated particles with KCN results in hollow hydrogel nanoparticles. The rate of Au core etching as studied by the decrease in Au nanoparticle plasmon absorbance was shown to depend on polymer shell composition, shell thickness, and the thermosensitivity of the polymer. Efficient quenching of fluorophores incorporated in the polymer shell by the core Au nanoparticles was observed; however, the shell fluorescence was regained after core dissolution. Future studies are aimed at understanding the encapsulation of small molecules and proteins within the nanocapsule structure.