Semiconductor ZnO based photosensitizer core-shell upconversion nanoparticle heterojunction for photodynamic therapy

Photodynamic therapy (PDT) as a noninvasive technique is widely used to treat cancer diseases due to its low side effects. PDT based on upconversion nanoparticles (UCNPs) improved tissue penetration and photo-stability. However, traditional photosensitizers and UCNPs were difficult to incorporate, which limited the circulation of the UCNPs in blood and decreased the PDT effect. Herein, we designed NaErF₄@ZnO UCNPs for potential application in thyroid tumor cell PDT. With ZnO coated on NaErF₄, the blue (415 nm), green (525 nm/545 nm) and red (661 nm) upconversion luminescence enhanced compared with that of NaErF₄ core nanoparticles. Particularly, the generation of UV upconversion emission by NaErF₄ sensitized ZnO, which catalyzed H₂O and O₂ to produce ROS reactive oxygen species (ROS) to induce papillary thyroid carcinoma (PTC) cell lines BHP 5-16. With 1000 μg mL^-1 of NaErF₄@ZnO UCNPs, the viability of BHP 5-16 cells decreased to about 41% as measured by CCK8 assay with 980 nm NIR irradiation. Moreover, it was confirmed that NaErF₄@ZnO UCNPs had low toxicity for BHP 5-16 cells. All these results indicated that NaErF₄@ZnO upconversion nanoparticles were an excellent platform for PDT treatment.