In vivo pharmacokinetics, long-term biodistribution and toxicology study of functionalized upconversion nanoparticles in mice

We investigated the in vivo pharmacokinetics, long-term biodistribution and toxicology of polymercoated upconversion nanoparticles (UCNPs) in mice. Materials & Methods: Near infrared emitting Yb3+/Tm3+-doped NaYF4 UCNPs coated with either polyethylene glycol (PEG) or polyacrylic acid (PAA) were intravenously injected into mice. Blood levels of UCNPs were measured. Yttrium levels in various organs were measured to determine the biodistribution of UCNPs over 3 months. Serum biochemistry, hematology and histology assays were conducted for in vivo toxicology assays. Results: UCNP-PEG exhibited improved stability in physiological solutions and prolonged blood circulation half-lives more than UCNP-PAA. No noticeable toxic side effect was noticed for either UCNP-PAA or UCNP-PEG in our toxicology study, despite the long-term retention of those nanoparticles in the reticuloendothelial systems including the liver and spleen of mice. Conclusion: Although more systematic investigations are still required, the absence of appreciable toxicity shown in our study encourages future explorations of UCNPs for in vivo biomedical applications.