Multifunctional core–shell upconversion nanoparticles for targeted tumor cells induced by near-infrared light

Here we synthesize silica-coated NaYF4:Yb/Er nanocomposites with a photosensitizer hypericin covalently bound to silica shells (UCNPs@SiO2@hypericin) successfully, exhibiting precise size-control, good water dispersity and excellent biocompatibility. Under near-infrared light (NIR) irradiation, UCNPs convert NIR light to strong green light which agrees well with the absorbance peak of the photosensitizer hypericin, and triggers hypericin to generate singlet oxygen effectively. The cell apoptosis studies by flow cytometry, fluorescence microscope imaging with Annexin V-FITC/PI and caspase-3 western blotting demonstrate that UCNPs@SiO2@hypericin-FA displays outstanding performance in the induction of apoptosis of Hela cells and HepG2 cells under NIR light irradiation for a short time. At the same time, UCNPs@SiO2@hypericin-FA nanocomposites are proved to exhibit little cytotoxicity by cell viability experiments. By the use of confocal microscopy, cell uptake results show that folate receptor FR(+) cell lines such as Hela cells could internalize more UCNPs@SiO2@hypericin-FA than FR(−) cell lines, such as 293T cells, with highly selective cellular uptake. All the results indicate that UCNPs@SiO2@hypericin-FA nanocomposites have a promising potential in the application of PDT and other diseases in deep tissues.