(598a) Thermal Decomposition Synthesis of Monodisperse, Phase-Pure Iron Oxide Nanoparticles for Mpi and Magnetic Hyperthermia Applications

Thermal decomposition syntheses are often the method of choice to produce highly crystalline inorganic metal and metal oxide nanoparticles with tightly controlled physical size and shape distributions. A hallmark of the thermal decomposition synthesis is that it is typically performed in inert atmospheres, because the reaction temperature is often above the flash point of the organic solvent. However, such conditions may be unfavorable to the formation of phase pure metal oxide particles. For iron oxide nanoparticles, the anoxic conditions in the reactor favor the formation of nanoparticles with a mix of magnetic and non-magnetic domains or phases and the magnetic properties are poorly controlled and sub-par compared to bulk crystals. This poses a critical limitation, since the exact nature of the nanoparticles’ response to externally applied static or time-varying magnetic fields forms the basis for their use in many applications, and this response is directly related to the nanoparticle’s magnetic properties.

Methods to manipulate crystal phase and promote the formation of magnetite have been reported, either through post-synthesis oxidation or by tuning the electrochemical redox potential of the reaction mixture during synthesis. However, the reported syntheses still offer limited tunability in size. To overcome this limitation, our group has explored controlled addition of molecular oxygen to promote in situ oxidation of the nanoparticles during growth, and we have shown that phase-pure magnetite nanoparticles with magnetic properties approaching those of bulk magnetite could be synthesized reproducibly with fine control in size over the range of 10-20 nm. Here we report efforts to extend this size range to 10-40 nm and improve reproducibility of nanoparticle synthesis. First, we improved reproducibility of the iron oleate precursor synthesis, as we believe variability in the chemical structure of the oleate prevented us from obtaining particles larger than 20 nm. Next, we explore the reaction parameter space to identify conditions over which monodisperse iron oxide nanoparticles can be grown reproducibly, both in an inert atmosphere and with controlled molecular oxygen addition to promote the formation of phase-pure magnetite with magnetic properties approaching those of the bulk. Finally, we characterize these particles for their potential biomedical applications in magnetic hyperthermia and the new molecular imaging modality called magnetic particle imaging.