Advances of Upconversion Nanoparticles for Molecular Imaging

Molecular imaging is developing fast towards multi-modality and simultaneous therapy. For molecular imaging, up conversion nanoparticles (UCNPs), especially lanthanide-doped nanocrystalsown obvious advantages such as low toxicity,large Stokes shifts, high resistance to photo-bleachingand photochemical degradation. Moreover,near infrared(NIR)excitation contributes to the auto-fluorescenceminimization, a larger penetrating depth, and lessharmfulness to cellscompared with traditional ultraviolet (UV) excitation. On the other hand, the composites of UCNPs withbiological target moleculesexertsuperior performance, broadening theirbiological application scope from multi-modality imaging, to simultaneous drug delivery and targeted therapy. Herein, we review main advances of UCNPs applied to tumor multi-modality imaging and simultaneous therapy over the past few years, explore their application prospects, and discuss the concepts, issues, approaches, and challenges, with the aim of improving the application of UCNPs in biomedical imaging and therapy in near future.