Radioisotope post-labeling upconversion nanophosphors for in vivo quantitative tracking

Lanthanide based upconversion nanophosphors (UCNPs) attracted increasing attention for potential applications in bioimaging, while its in vivo behaviors are not clear until now due to no available quantification imaging tools. Herein, we developed a unique rare-earth cation-exchange-based postlabelling method to introduce 153Sm into the lattice of UCNPs, providing this 153Sm-postlabeling UCNP having bifunction of radioactive property and upconversion luminescence under excitation at 980 nm laser. This 153Sm-postlabelling method shows rapid treatment time of <1 min, high labeling yield of >99%, and without usage of organic solvents. More importantly, this 153Sm-postlabelling method is also suitable for most of rare earth nanoparticles to track their in vivo behaviors. The dynamic quantification studies of the in vivo fate of the rare-earth nanoparticles were further investigated by radioactive detection method such as single-photon emission computed tomography (SPECT) and gamma counter. The imaging results revealed that UCNPs were mainly captured by the mononuclear phagocyte system (liver and spleen). The amount of nanoparticles in liver arrived at its peak quicker and was about 15 fold of that in spleen. And the nanoparticles will be slowly excreted with the bile. Therefore, the concept of postlabeling 153Sm onto lanthanide-based UCNPs may serve as a facile strategy of fabricating multifunctional nanoprobes for upconversion luminescence (UCL) and SPECT dual-modality imaging.