Fig. 4.

Drug release behavior of TR-UCNS. a DOX release behavior of TR-UCNS aqueous dispersion (0.5 mg ml⁻¹) under external heating. The temperature varied from 32 to 47 °C. The release rate was normalized to 47 °C. It should be noted that the release rate at 41.5 °C reached to ~90%. b DOX release rate of TR-UCNS aqueous dispersion (0.5 mg ml⁻¹) versus time upon 730 nm laser irradiation (50 mW cm⁻²). Error bars were defined as s.d. (n = 3). The eigen temperature and apparent temperature of TR-UCNS reached 41.6 and 37.8 °C, respectively. In control experiments, the temperature of the solution was kept at 37 and 37.8 °C, and the release rate was much lower than that achieved by laser irradiation. These results indicate that eigen temperature during photothermal therapy is the key factor for drug release