Dual-modality in vivo imaging using rare-earth nanocrystals with near-infrared to near-infrared (NIR-to-NIR) upconversion luminescence and magnetic resonance properties

Upconversion luminescence (UCL) imaging is expected to play a significant role in future photoluminescence imaging since it shows advantages of sharp emission lines, long lifetimes, superior photostability and no blinking. To further improve penetration depth, herein, near-infrared to near-infrared (NIR-to-NIR) UCL and magnetic properties were combined into a nanoparticle, and NIR-to-NIR UCL and MRI dual-modal bioimaging in vivo of whole-body animal were developed. Hydrophilic and carboxylic acid-functionalized Tm3+/Er3+/Yb3+ co-doped NaGdF4 upconversion nanophosphors (AA-NPs) were synthesized and showed both NIR-to-visible and NIR-to-NIR luminescence under excitation of 980 nm. Collecting the signal of the upconversion emission from AA-NPs in the visible and NIR range, all UCL imaging of cells, tissues and whole-body animals with different penetration depth showed high contrast. Moreover, AA-NPs showed a high relaxivity of 5.60 s−1 (mm)−1 and were successfully applied as contrast agents for magnetic resonance imaging (MRI) in vivo. By means of the combination of UCL imaging and MRI, the distribution of AA-NPs in living animals was studied, and the results indicated that these particles mainly accumulate in the liver and spleen without undesirable stay in the lungs. Therefore, the concept of UCL and MR dual-modality imaging in vivo of whole-body animals using Tm3+/Er3+/Yb3+ co-doped NaGdF4 with NIR-to-NIR upconversion luminescent and magnetic resonance properties can serve as a platform technology for the next-generation of probes for bioimaging in vivo.