Biocompatible and Superparamagnetic Manganese-Doped Iron Oxide Nanoclusters for Diagnostic Applications

Multimodal imaging strategies that integrate multiple images improve the accuracy of clinical diagnosis and the outcomes of treatment. It is important to seek a simpler solution for multimodal probes that can be more easily translated into clinical use rather than overengineering and complex syntheses. Here, we engineered manganese-doped iron oxide nanoclusters (MnIO NCs) composed of manganese-doped iron oxide nanoparticles (MnIO NPs) using a particularly simple and efficient one-pot approach. MnIO NCs possess excellent water-solubility, colloidal stability, biocompatibility, and superparamagnetic properties. The overall size of MnIO NCs is 44–58 nm, and the size of primary MnIO NPs is 4.6–5.8 nm. MnIO NCs significantly enhanced both T1 relaxivity (r1 = 4.86 mM–1 s–1, higher than that of Magnevist) and T2 relaxivity (r2 = 365.5 mM–1 s–1, ca. 5 times higher than that of Fe3O4 nanoparticles, 5 times higher than that of Resovist, and 9 times higher than that of Feridex). These results demonstrate the great potential of MnIO NCs in T1–T2 dual-mode magnetic resonance imaging for deep tissue. This work provides a very feasible, simple, and effective method for the synthesis of magnetic nanomaterials that are needed in large quantities.