Upconversion nanoparticles@AgBiS core-shell nanoparticles with cancer-cell-specific cytotoxicity for combined photothermal and photodynamic therapy of cancers.

UCNPs@AgBiS core-shell nanoparticles that AgBiS coated on the surface of upconversion nanoparticles (UCNPs) was successfully prepared through an ion exchange reaction. The photothermal conversion efficiency of AgBiS can be improved from 14.7% to 45% due to the cross relaxation between Nd ions and AgBiS. The doping concentration of Nd ions played a critical role in the production of reactive oxygen species (ROS) and enhanced the photothermal conversion efficiency. The NaYF:Yb/Er/Nd@NaYF:Nd nanoparticles endows strong upconversion emissions when the doped concentration of Nd ions is 1% in the inner core, which excites the AgBiS shell to produce ROS for photodynamic therapy (PDT) of cancer cells. As a result, the as-prepared NaYF:Yb/Er/Nd@NaYF:Nd@AgBiS core-shell nanoparticles showed combined photothermal/photodynamic therapy (PTT/PDT) against malignant tumors. This work provides an alternative near-infrared light-active multimodal nanostructures for applications such as fighting against cancers.