Magnetic resonance imaging of Fe3O4@SiO2-labeled human mesenchymal stem cells in mice at 11.7 T

Fe3O4@SiO2 core–shell nanoparticles were synthesized and used to label human mesenchymal stem cells (hMSCs) for in vitro and in vivo magnetic resonance imaging study. The diameter of the nanoparticles is 24–30 nm with a Fe3O4 core of ∼8 nm and a SiO2 shell of ∼8 nm. Transverse relaxivity of the nanoparticles dispersed in water is measured to be ∼106 mM−1 s−1. After incubation with hMSCs for 12 h at a concentration of 100 μg Fe/mL, cellular uptake of Fe3O4@SiO2 is 20–100 pg Fe/cell, which are located predominantly in the cytoplasm of cells. This level of uptake exhibits no significant influence on hMSCs' viability and differentiation. In vitro imaging of Fe3O4@SiO2-labeled hMSCs evenly distributed in agarose gel yields single cell sensitivity at 11.7 T. In vivo imaging of Fe3O4@SiO2-labeled hMSCs injected into the left brain hemisphere of nude mice yields imaging sensitivity of ∼130 hMSCs.