Upconversion nanoparticles@single-walled carbon nanotubes composites as efficient self-monitored photo-thermal agents.

Conventional photothermal therapy (PTT) usually relies on a macroscopic heat source to raise the temperature of tissues to 41-45 °C, which not only kills the pathological cells but causes severe side effects on nearby normal tissues, thus reducing the accuracy of PTT. Here we successfully fabricated nanocomposites of NaYF4:Yb3+,Tm3+@NaYF4:Yb3+@SiO2-SWCNTs, in which the upconversion nanoparticles (UCNPs) serve as real-time temperature-feedback moiety and the single-walled carbon nanotubes (SWCNTs) serve as efficient nano-heaters. The sample displays an excellent photothermal conversion capacity, i.e., the temperature of the aqueous dispersion increases from 23.3 °C up to 60.1 °C under 980 nm excitation due to the intense absorption and highly efficient heat generation of SWCNTs. Meanwhile, the temperature of the nanocomposites is monitored in real time based on the fluorescent intensity ratio of UCNPs. The in-vitro experiments demonstrate that the temperature of the nanocomposites at tissue injection of 1 mm can reach PTT temperature of 42.2 °C with a facile surrounding temperature of 36.2 °C under moderate laser power (980 nm, 2.0 W cm-2). These results provide a novel design for multifunctional nanocomposites that enable safe and controlled PTT.