Composition Tunable Manganese Ferrite Nanoparticles for Optimized T2 Contrast Ability

Manganese-doped magnetite nanoparticles as magnetic resonance imaging (MRI) contrast agents have been well developed in recent years due to their higher saturation magnetization and stronger transverse (T2) contrast ability compared to parent magnetite. However, the underlying role that manganese doping plays in altering the contrast ability of magnetite is still not thoroughly understood. Herein, we investigate the effects of manganese doping on changes of ferrite crystal structures, magnetic properties, and contrast abilities. We developed a successful one-pot synthesis of uniform manganese-doped magnetite (MnxFe3–xO4) nanoparticles with different manganese contents (x = 0–1.06). The saturation magnetization and T2 contrast ability of ferrite nanoparticles increase along with rising manganese proportion, peak when the doping level of MnxFe3–xO4 reaches x = 0.43, and decrease dramatically as the manganese percentage continues to augment. At high manganese doping level, the manganese ferrite nanoparticles may undergo lattice distortion according to analysis of XRD patterns and lattice distances, which may result in low saturation magnetization and eventually low T2 contrast ability. The MnxFe3–xO4 nanoparticles (x = 0.43) with a diameter of ∼18.5 nm exhibit the highest T2 relaxivity of 904.4 mM–1 s–1 at 7.0 T among all the samples and show a much stronger T2 contrast effect for liver imaging than that of other iron oxide contrast agents. These results indicate that the optimized T2 contrast ability of manganese ferrite nanoparticles could be achieved by tuning the manganese doping level. This work also opens a new field of vision for developing high-performance T2 contrast agents by modulating the metal composition of nanoparticles.