Microgels loaded with gold nanorods: photothermally triggered volume transitions under physiological conditions.

Photothermally driven volume transitions in polymer microgels have promising applications for site-specific drug delivery and photodynamic therapy. We studied the temperature-induced volume phase transitions for a series of thermoresponsive microgels of various compositions to find a system with a sharp transition in the physiologically relevant range spanning 38-41 degrees C in 0.01 M phosphate-buffered saline solution (pH = 7.4). We found that the poly(N-isopropylacrylamide-maleic acid) microgels showed an 8-fold decrease in size under the aforementioned conditions. These microgels were loaded with gold nanorods designed to absorb in the near-IR spectral range. Following irradiation at lambda = 809 nm, the microgels underwent a large, reversible, photothermally triggered change in volume. We believe that this microgel system is a promising candidate for photothermally controlled drug release.