Liquid phase synthesis of spinel-structured ferrimagnetic iron oxide nanoparticles for magnetic hyperthermia

In recent years, magnetic hyperthermia is being focused on as a non-invasive approach in cancer treatment. Spinel-structured iron oxide nanoparticles, namely Fe₃O₄ and γ-Fe₂O₃ are among the suitable candidates for magnetic hyperthermia and thermal ablation therapies due to their high biocompatibility and chemical stability. In the application of ferrimagnetic iron oxide nanoparticles to hyperthermia, coercive force control is an important requirement for effective hysteresis-loss heating within the human-safe limit amplitude and frequency of magnetic field. Coercive force control for spherical spinel structured iron oxide nanoparticles can be achieved by doping the particles with cobalt which changes the crystalline anisotropy. However due to the toxicity of cobalt, we attempted to attain coercive force control by introducing the shape anisotropy and synthesized platelet γ-Fe₂O₃ nanoparticles from the reduction process of platelet α-FeOOH in H₂ gas [1]. The coercive force, which depends on the platelet shape anisotropy was in the range of 8-14 kA/m. During the H₂ gas reduction process, SiO₂ coating which was essential to prevent sintering of particles during high annealing temperature reduces the magnetization per unit volume which can affect the heating ability of the particles.