Bi-Magnetic Core-Shell CoFe₂O₄@MnFe₂O₄ Nanoparticles for In Vivo Theranostics

In this work, we report the synthesis and characterization of three magnetic nanosystems, CoFe₂O₄, CoFe₂O₄@ZnFe₂O₄, and CoFe₂O₄@MnFe₂O₄, which were developed as potential theranostic agents for magnetic hyperthermia and magnetic resonance imaging (MRI). These nanosystems have been thoroughly characterized by X-ray Diffraction (XRD), Transmission Electron Miscroscopy (TEM), Dark Field-TEM (DF-TEM), Vibrating Sample Magnetometry (VSM), and inductive heating, in order to elucidate their structure, morphology, and magnetic properties. The bi-magnetic CoFe₂O₄@ZnFe₂O₄ and CoFe₂O₄@MnFe₂O₄ nanoparticles (NPs) exhibited a core-shell structure with a mean average particle size of 11.2 ± 1.4 nm and 14.4 ± 2.4 nm, respectively. The CoFe₂O₄@MnFe₂O₄ NPs showed the highest specific absorption rate (SAR) values (210–320 W/g) upon exposure to an external magnetic field, along with the highest saturation magnetization (Ms). Therefore, they were selected for functionalization with the PEGylated ligand to make them stable in aqueous media. After the functionalization process, the NPs showed high magnetic relaxivity values and very low cytotoxicity, demonstrating that CoFe₂O₄@MnFe₂O₄ is a good candidate for in vivo applications. Finally, in vivo MRI experiments showed that PEGylated CoFe₂O₄@MnFe₂O₄ NPs produce high T₂ contrast and exhibit very good stealth properties, leading to the efficient evasion of the mononuclear phagocyte system. Thus, these bi-magnetic core-shell NPs show great potential as theranostic agents for in vivo applications, combining magnetic hyperthermia capabilities with high MRI contrast.