Biodistribution of sub-10 nm PEG-modified radioactive/upconversion nanoparticles.

The biodistribution of lanthanide-based upconversion nanophosphors (UCNPs) has attracted increasing attention, and all of the reported UCNPs display metabolism in the liver and spleen mainly. Herein, ∼8 nm poly(ethylene glycol) (PEG)-coated NaYF4 nanoparticles codoped with Yb(3+), Er(3+), and (or) radioactive (153)Sm(3+) ions were synthesized, through a hydrothermal synthetic system assisted by binary cooperative ligands with oleic acid and PEG dicarboxylic acids. The as-prepared PEG-coating NaYF4:Yb,Er and NaYF4:Yb,Er,(153)Sm are denoted as PEG-UCNPs and PEG-UCNPs((153)Sm), respectively. PEG-UCNPs were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FTIR) spectroscopy. The PEG-UCNPs showed excellent water solubility with a hydrodynamic diameter of ∼10 nm and displayed upconversion luminescence (UCL) under continuous-wave excitation at 980 nm. At the same time, the (153)Sm-doped nanoparticles PEG-UCNPs((153)Sm) displayed radioactivity, and time-dependent biodistribution of PEG-UCNPs((153)Sm) was investigated, through single-photon emission computed tomography (SPECT) imaging and γ-counter analysis. Interestingly, PEG-UCNPs((153)Sm) had a long blood retention time and were partly eliminated through urinary pathways in vivo. Therefore, the concept of fabricating PEG-coated, small nanosize (sub-10 nm) nanoparticles with radioactive property is a useful strategy for providing a potential method to monitor lanthanide nanoparticles renal clearable.