A cell penetrating peptide-modified magnetic/fluorescent probe for in vivo tracking of mesenchymal stem cells

Difficulty in precise tracking of the in vivo distribution and migration of transplanted stem cells in a noninvasive way is a great hurdle in regenerative medicine research. Paramagnetic element-doped upconversion nanoparticles (UCNPs) emerge as a kind of promising dual-modal imaging agents owing to the possibility in combining strong contrast of MR imaging and high efficiency of fluorescence imaging. Herein a kind of Mn-doped NaYF4-based UCNPs (NaYF4: 20%Yb, 2%Er, 30%Mn) was developed and then hydrophilized by various coatings, including cell penetrating peptide, DNA, and SiO₂ . The UCNPs were denoted as Pep/UCNPs, DNA/UCNPs, and SiO₂ /UCNPs, respectively. Their potential in cell labeling and in vivo tracking applications was comprehensively explored. The results show that the Mn-doped UCNPs possess high biocompatibility, high cell labeling efficiency, high MR resolution, and importantly a single emission at 660 nm, within optical window for in vivo imaging of biological targets. Particularly, mesenchymal stem cells (MSCs) pre-labeled by cell penetrating peptide-modified UCNPs (Pep/UCNPs) can be precisely monitored in terms of their distribution in mice over a long period of time by simultaneous MR and fluorescent imaging, which provided a noninvasive and double-checking tool for investigating the destination of stem cells in tissue regeneration.