NaYF4:Yb3+/Tm3+@NaYF4:Yb3+Upconversion Nanoparticles for Optical Temperature Monitoring and Self-Heating in Photothermal Therapy

The core-shell NaYF4:Yb3+/Tm3+@NaYF4:Yb3+ upconversion nanoparticles were successfully prepared by a solvothermal method, and a layer of mesoporous silica (mSiO2) was successfully coated on the periphery of the core-shell nanoparticles to transform their surface from lipophilic to hydrophilic, further expanding their applications in biological tissues. The physical phase, morphology, structure, and fluorescence properties were characterized by X-ray diffraction (XRD), field emission transmission electron microscopy (TEM), Fourier infrared spectroscopy (FT-IR), zeta potential analysis, and fluorescence spectroscopy. It was found that the material has a hexagonal structure with good hydrophilicity and emits intense fluorescence under 980 nm pump laser excitation. The non-contact temperature sensing performance of nanoparticles was evaluated by analyzing the upconversion fluorescence of Tm3+ (1G4-* 3F4 and 3F3-* 3H6) in the temperature range of 284-344 K. The absolute and relative sensitivities were found to be 0.0067 K-1 and 1.08 % K-1, respectively, with high-temperature measurement reliability and good temperature cycling performance. More importantly, its temperature measurement in phosphate-buffered saline (PBS) solution is accurate. In addition, the temperature of the cells can be increased by adjusting the laser power density and laser irradiation time. Therefore, an optical temperature sensing platform was built to realize the of real-time of cancer cell and the dual function of

Automated summary

The core-shell NaYF4:Yb3+/Tm3+@NaYF4:Yb3+ upconversion nanoparticles were prepared successfully by a solvothermal method and coated with mesoporous silica (mSiO2) to enhance their hydrophilicity. The nanoparticles demonstrated good temperature sensing performance and intense fluorescence emission. They also showed high reliability and accuracy in temperature measurement in phosphate-buffered saline (PBS) solution. This study provides a potential platform for real-time temperature monitoring and thermotherapy of cancer cells.