Core-shell magnetic nanoparticles: harnessing synergistic effects for MRI and magnetic hyperthermia

Magnetic theranostic nanoparticles (NPs) that offer simultaneous magnetic resonance imaging (MRI) contrast enhancement and magnetic hyperthermia therapy hold great potential for cancer diagnosis and treatment. However, achieving dual functionalities in a single nanoscale platform remains a significant challenge. To address this, we develop core-shell iron oxide (IO)@manganese oxide (MO) nanoparticles via a seed-mediated thermal decomposition method. The biocompatible IO core provides efficient magnetic hyperthermia, while the MO shell enhances MRI contrast through its paramagnetic properties. Our method produces well-defined core-shell NPs with strict control of MO shell thickness, overcoming the challenge posed by the high surface energy of MO, which typically leads to non-uniform coating or separate nucleation of MO. Our findings reveal that the MO shell not only enhances their MRI relaxivities (both T1 and T2) but also mitigates the adverse effect of dipolar interactions, thereby improving their heating efficiency in magnetic hyperthermia at clinically relevant concentrations (>12 mg/mL). Our work uncovers that the influence of the MO shell on heating performance is primarily due to a reduction in saturation magnetization arising from the interaction of the ferrimagnetic core with the paramagnetic shell, unlike changes in magnetic anisotropic energy barrier or Néel relaxation, as previously reported. Our findings offer new insights into designing novel core-shell nanotheranostic agents, paving the way for more effective MRI-guided therapies that combine high-precision MRI imaging with magnetic hyperthermia.