Mn2+ Dopant-Controlled Synthesis of NaYF4:Yb/Er Upconversion Nanoparticles for in vivo Imaging and Drug Delivery----Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety

Here, we represent a facile strategy for the rational manipulation of green and red upconversion emission, and the pure dark red emission (650-670nm) of NaYF4: Yb/Er UCNPs has been achieved by manganese ions (Mn2+) doping. The existence of Mn2+ ions disturbs the transition possibilities between green and red emissions of Er3+ and facilitates the occurrence of red emission, resulting in an emission color output from green to red by rational controlling the Mn2+-doping level. Moreover, the Mn2+-doping also influences the growth dynamics to give simultaneous control of crystalline phase and size of the resulting UCNPs. By coating a PEG phospholipid layer on the surface of the NPs, the as-prepared UCNPs ware rendered water-soluble and then employed as luminescent probes for in vivo imaging. In addition, these PEGlyated UCNPs could also be employed as drug delivery carriers. A commonly used chemotherapeutic drug, doxorubicin (DOX), was loaded on these PEGylated UCNPs by physical adsorption through simple mixing. The release of DOX from UCNPs can be controlled by varying pH values, facilitating its drug delivery and controlled release to cancer cells. As a result, the as-prepared UCNPs with efficient red upconversion luminescence and drug delivery capabilities could be potentially employed as a platform for simultaneous in vivo bioimaging and therapeutic applications.