Dually functioned core-shell NaYF(4):Er(3+)/Yb(3+)@NaYF(4):Tm(3+)/Yb(3+) nanoparticles as nano-calorifiers and nano-thermometers for advanced photothermal therapy

To realize photothermal therapy (PTT) of cancer/tumor both the photothermal conversion and temperature detection are required. Usually, the temperature detection in PTT needs complicated instruments, and the therapy process is out of temperature control in the present investigations. In this work, we attempt to develop a novel material for achieving both the photothermal conversion and temperature sensing and control at the same time. To this end, a core-shell structure with NaYF(4):Er(3+)/Yb(3+) core for temperature detection and NaYF(4):Tm(3+)/Yb(3+) shell for photothermal conversion was designed and prepared. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, the temperature sensing properties for the NaYF(4):Er(3+)/Yb(3+) and core-shell NaYF(4):Er(3+)/Yb(3+)@NaYF(4):Tm(3+)/Yb(3+) nanoparticles were studied. It was found that the temperature sensing performance of the core-shell nanoparticles did not become worse due to coating of NaYF(4):Tm(3+)/Yb(3+) shell. The photothermal conversion behaviors were examined in cyclohexane solution based on the temperature response, the NaYF(4):Er(3+)/Yb(3+)@NaYF(4):Tm(3+)/Yb(3+) core-shell nanoparticles exhibited more effective photothermal conversion than that of NaYF(4):Er(3+)/Yb(3+) nanoparticles, and a net temperature increment of about 7 °C was achieved by using the core-shell nanoparticles.