(275b) Effect of Post-Synthesis Oxidation on Magnetic Particle Imaging (MPI) Performance

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. Synthesis methods reported to improve magnetic properties include in-situ oxidation and post-synthesis oxidation. This study focuses on the latter using a parallel-synthesis approach to perform 8 syntheses simultaneously, accelerating data collection and enabling statistical analysis of particle properties and performance. Two control groups were synthesized without post-synthesis oxidation, meanwhile two groups underwent post-synthesis oxidation with a 1% O₂ in argon mixture at 300 °C for either 3 or 30 hours. Characterization consisted of TEM for physical diameters, and SQUID magnetometry for M-H curves to determine magnetic diameters and saturation magnetization. MPI performance was obtained from relaxation scans, both signal intensity and resolution, showing significant improvement for the post-synthesis oxidation groups. Correlations and statistical analysis suggest that the following tracer properties most strongly influence MPI performance: magnetic diameter and its distribution, difference between the physical and magnetic diameter, and physical aspect ratio.