(269g) Thermal Decomposition Synthesis of Iron Oxide Nanoparticles in a Precision Machined Reactor with Enhanced Gas-Liquid Mass Transfer for Magnetic Particle Imaging (MPI)

Magnetic nanoparticles are of great interest for biomedical applications due to their ease of synthesis, biocompatibility, and tunable physicochemical and magnetic properties. Magnetic Particle Imaging (MPI) is a novel molecular imaging modality relying on the nonlinear magnetization of superparamagnetic iron oxide nanoparticle (SPION) tracers in a time-varying magnetic field, which has potential for applications in blood pool imaging, magnetic hyperthermia, magnetically triggered drug release, and tracking cell therapies. Modeling of MPI physics suggests that iron oxide nanoparticles larger than 25 nm with uniform magnetic properties would achieve optimal performance, meaning high signal intensity and resolution. The challenge of synthesizing these tracers is that as size increases, the probability of defects and multiple crystal structures forming within a particle increases, impairing magnetic properties and hindering MPI performance. Previous efforts in our group have demonstrated that oxygen addition during synthesis can eliminate the magnetic dead layer often reported to explain suboptimal magnetic properties. This in-situ oxidation method has allowed our group to develop 21 nm tracers for MPI (RL-1) with magnetic properties similar to bulk magnetite, yielding 4x better sensitivity than commercial tracer Ferucarbotran. We hypothesize the method’s limited success for larger particles (> 20 nm) is due to gas-liquid mass transfer limitations, which has been a barrier to synthesize tracers with superior sensitivity and resolution. To overcome this limitation, we are adopting use of a machined reactor with a gas entrainment impeller that bubbles the gas in the reactor’s headspace into the reaction mixture. Synthesis conditions of our developed tracers (RL-1) were tested in the new reactor using various solvents. The effect of factors such as reactor surface, surfactant concentration, and precursor addition rates on nanoparticle growth kinetics, size distribution and morphology were explored. Our work shows the process of optimizing and troubleshooting a new reactor system for magnetic nanoparticle synthesis, which ultimately will lead to reproducible nanoparticles with superior magnetic properties and MPI performance.