NIR-Triggered Generation of Reactive Oxygen Species and Photodynamic Therapy Based on Mesoporous Silica-Coated LiYF(4) Upconverting Nanoparticles

To date, the increase in reactive oxygen species (ROS) production for effectual photodynamic therapy (PDT) treatment still remains challenging. In this study, a facile and effective approach is utilized to coat mesoporous silica (mSiO(2)) shell on the ligand-free upconversion nanoparticles (UCNPs) based on the LiYF(4) host material. Two kinds of mesoporous silica-coated UCNPs (UCNP@mSiO(2)) that display green emission (doped with Ho(3+)) and red emission (doped with Er(3+)), respectively, were successfully synthesized and well characterized. Three photosensitizers (PSs), merocyanine 540 (MC 540), rose bengal (RB), and chlorin e6 (Ce6), with the function of absorption of green or red emission, were selected and loaded into the mSiO(2) shell of both UCNP@mSiO(2) nanomaterials. A comprehensive study for the three UCNP@mSiO(2)/PS donor/acceptor pairs was performed to investigate the efficacy of fluorescence resonance energy transfer (FRET), ROS generation, and in vitro PDT using a MCF-7 cell line. ROS generation detection showed that as compared to the oleate-capped and ligand-free UCNP/PS pairs, the UCNP@mSiO(2)/PS nanocarrier system demonstrated more pronounced ROS generation due to the UCNP@mSiO(2) nanoparticles in close vicinity to PS molecules and a higher loading capacity of the photosensitizer. As a result, the three LiYF(4) UCNP@mSiO(2)/PS nanoplatforms displayed more prominent therapeutic efficacies in PDT by using in vitro cytotoxicity tests.