Bio-mimetically synthesized hematite/maghemite nanoparticles used for efficient positive magnetic resonance angiography

The nano-sized ferromagnetic ferritin cage nanoparticles are not only ideal for understanding of superparamagnetism, but also promising in application for biomedicine and clinical usages. Herein, we synthesized ultrafine ferritin-based iron oxide (hematite/maghemite) nanoparticles with an averaged core size ranges from 1.6 nm to 4.7 nm by controlled biomimetic mineralization using genetically recombinant human H chain ferritin. Magnetic analysis showed that both the saturation magnetization (Ms) and blocking temperature (Tb) were increased with the size of ferrimagnetic cores. In essence, magnetic resonance imaging (MRI) analysis showed that 2.2 nm sized magnetoferritin (hereafter named as M-HFn-2.2) shows r₁ value of 0.86 mM^-1s^-1 and r₂/r₁ ratio of 25.1. Blood pool imaging on mice using the M-HFn-2.2 nanoparticles, which was injected through a tail vein by single injection enabled detecting detailed vascular nets at 3 minutes post injection. The signal intensity continuously enhanced up to 2 hours post injection, which is much longer than the commercial magnevist (Gd-DTPA) contrast. Moreover, biodistribution examination indicated that organs of liver, spleen and kidney safely cleared the injected nanoparticles within one day after the injection, demonstrating no risk of iron overload in the tested mice. Therefore, this study sheds light on developing novel high-performance gadolinium-free positive magnetic resonance contrast agents for biomedical applications.