Increasing the Magnetic Anisotropy of a Natural System: Co-Doped Magnetite Mineralized in Ferritin Shells

Enhanced Magnetic Hyperthermia of Magnetoferritin through Synthesis at Elevated Temperature

Iron oxide nanoparticles have attracted a great deal of research interest in recent years for magnetic hyperthermia therapy owing to their biocompatibility and superior thermal conversion efficiency. Magnetoferritin is a type of biomimetic superparamagnetic iron oxide nanoparticle in a ferritin cage with good monodispersity, biocompatibility, and natural hydrophilicity. However, the magnetic hyperthermic efficiency of this kind of nanoparticle is limited by the small size of the mineral core as well as its low synthesis temperature. Here, we synthesized a novel magnetoferritin particle by using a recombinant ferritin from the hyperthermophilic archaeon Pyrococcus furiosus as a template with high iron atom loading of 9517 under a designated temperature of 90 °C. Compared with the magnetoferritins synthesized at 45 and 65 °C, the one synthesized at 90 °C displays a larger average magnetite and/or maghemite core size of 10.3 nm. This yields an increased saturation magnetization of up to 49.6 emu g-1 and an enhanced specific absorption rate (SAR) of 805.3 W g-1 in an alternating magnetic field of 485.7 kHz and 49 kA m-1. The maximum intrinsic loss power (ILP) value is 1.36 nHm2 kg-1. These results provide new insights into the biomimetic synthesis of magnetoferritins with enhanced hyperthermic efficiency and demonstrate the potential application of magnetoferritin in the magnetic hyperthermia of tumors.