High Affinity to Skeleton Rare Earth Doped Nanoparticles for Near-Infrared II Imaging.

As a newly noninvasive emerging modality, NIR-II fluorescence imaging (1000-1700 nm) has many advantages over conventional visible and NIR-I imaging (700-900 nm). Unfortunately, only a few NIR-II fluorophores are suitable for bone imaging. Here, we report an NIR-II fluorophore based on DSPE-mPEG encapsulated rare earth doped nanoparticles (RENPs@DSPE-mPEG), which shows inherent affinity to bone without linking any targeting ligands, and thus, it provides an alternative noninvasive and nonradiation strategy for skeletal system mapping and bone disease diagnoses. Interestingly, within the NIR-II window, imaging at a longer wavelength (1345 nm) provides a higher resolution and signal-to-noise ratio than imaging at 1064 nm, even though the quantum yield at 1064 nm is 2-fold higher than that at 1345 nm. Besides bone imaging, RENPs@DSPE-mPEG show an imaging application in blood vessels and lymph nodes. Importantly, RENPs@DSPE-mPEG can be internalized by circulating white blood cells. This finding may open a window to increase efficient nanoparticle delivery in the fields such as immunotherapy and improve the diagnostic and therapeutic efficacy of cancer-targeted nanoparticles in clinical applications.