Core/shell iron/iron oxide nanoparticles: are they promising for magnetic hyperthermia?

Core/shell iron/iron oxide nanoparticles have been proposed as a promising system for biomedical applications, because they combine a core (iron) with a high magnetic moment and a shell (iron oxide) with good biocompatibility. However, due to the interdiffusion of atoms between the core and the shell, with increasing time the core progressively shrinks until the particles eventually become hollow or nearly hollow, and as a result, the magnetic properties of these nanoparticles progressively deteriorate, negatively affecting their biomedical capabilities. In this article, we have studied the change of the morphology of the nanoparticles, from core/shell to hollow, depending on their size, and analyzed how this affects their magnetic and heating properties for magnetic hyperthermia. We have synthesized three core/shell samples with average sizes of 8, 12, and 14 nm. We have observed that with increasing size, the magnetic properties and the heating efficiency of the core/shell nanoparticles are improved and at the same time, they become more stable and retain their core/shell morphology for a longer period of time, making them more desirable for biomedical applications. As the nanoparticles become hollow, their saturation magnetization continuously decreases, and the heating efficiency also decays, rendering them less useful for magnetic hyperthermia application.