Carboxylic silane-exchanged manganese ferrite nanoclusters with high relaxivity for magnetic resonance imaging

To improve the magnetic properties and MRI contrast effect of Fe ₃O₄ superparamagnetic nanoparticles (NPs), a series of oleate-capped, Mn-doped Mn_xFe_(1-x)Fe₂O ₄ (x ≤ 0.4) NPs was prepared via a thermal decomposition method and subsequently assembled into nanoclusters by the carboxylic silane. The effects of Mn doping and clustering on the magnetization, relaxivity and contrast enhancement of the Mn_xFe_(1-x)Fe₂O ₄ (x ≤ 0.4) NPs were studied. Our results revealed that the Mn_xFe_(1-x)Fe₂O₄ NPs exhibited the highest saturation magnetization of 82.55 emu g^-1 when x = 0.05. Correspondingly, the assembled Mn_0.05Fe_(1-0.05)Fe ₂O₄ nanoclusters showed the highest relaxivity value of 528 (Mn + Fe) mM^-1 s^-1 and an enhanced MRI contrast in mouse liver. In addition, the MTT and H&E analysis confirmed that Mn _0.05Fe_(1-0.05)Fe₂O₄ nanoclusters were non-toxic. Therefore, the biocompatible Mn_0.05Fe _(1-0.05)Fe₂O₄ nanoclusters with superior relaxometric properties hold great potential in serving as a novel MRI nanoprobe.