From Core–Shell FeO/Fe₃O₄ to Magnetite Nanocubes: Enhancing Magnetic Hyperthermia and Imaging Performance by Thermal Annealing

High Resolution Image Download MS PowerPoint Slide We report the synthesis of mostly magnetite nanocubes (NCs) in the size range of 16–23 nm starting from FeO/Fe 3 O 4 core–shell NCs and employing a thermal decomposition method, followed by thermal treatment. To induce the phase transformation, the as-prepared NCs were thermally annealed either directly in an organic solvent before their transfer into water or by a thermal process in an aqueous solution after coating the NCs with an amphiphilic polymer shell to render them soluble in water. The effects of NCs’ size and type of post-synthesis annealing on improving their magnetic properties were investigated. The specific absorption rate (SAR) values, which measure the magnetic hyperthermia heating efficiency, were compared directly in water or in a viscous medium of glycerol/water mixtures to mimic the intratumoral dense environment. Among all samples, the 20 nm NCs annealed in organic solvent show the best heating capabilities. The 24 nm NCs exposed to the water annealing process are also able to achieve very high SAR values. Remarkably, all NC samples subjected to annealing exhibit heating efficiency values which are negligibly affected by the viscous media, thus demonstrating their unique SAR performance in a viscous-independent manner. For 20 nm NCs, a threefold higher magnetic particle imaging signal compared to the commercial tracer VivoTrax, and, at the same time, good magnetic resonance imaging contrast were measured.