Comparison of micrometer and nanometer sized magnetic particles for cell Labeling

Nanosized particles of iron oxide (NPIO) has been applied extensively as contrast medium for magnetic resonance imaging (MRI). Recently, micrometer sized particles of iron oxide (MPIO) has also been demonstrated the feasibility for cell labeling to monitor immune response. In this study, we compared the cellular labeling efficiencies of these two kinds of magnetic particles. The NPIO exhibit stronger saturation magnetization and produce more MRI signal change. On the contrary, MPIO revealed better particle uptake ability than NPIO in incubated cells. Microscopically, both MPIO and NPIO were located in the cytoplasm but not in the cell nucleus. On MRI examination,, MPIO labeled cells showed more pronounced signal change compared to NPIO labeled cells. We conclude that MPIO is more efficacious in cell labeling than NPIO. Further development and improvement of MPIO for its magnetization will facilitate its MRI applications on stem cell trafficking, evaluation of transplantation rejection and monitoring immune responses.