Flame-Made Doped Iron Oxide Nanoparticles as Tracers for Magnetic Particle Imaging

Magnetic particle imaging (MPI) is an emerging imaging modality that shows potential in tumor imaging, cell tracking, and angiography. It uses the signal generated from superparamagnetic iron oxide nanoparticles (SPIONs) with zero attenuation in tissue, showing excellent sensitivity and contrast. MPI resolution and sensitivity are dependent on the nonlinear dynamic magnetization of the SPION tracer and can be improved by tuning their magnetic properties. Doping SPIONs with manganese or zinc is an effective and biocompatible route to modify the magnetic properties of SPIONs. This study developed SPIONs doped with manganese or zinc as MPI tracers using flame spray pyrolysis (FSP), a highly scalable synthesis technique. The MPI performance was evaluated with a MOMENTUM imager. Postsynthesis citrate coating and filtration significantly enhanced the MPI resolution of SPIONs. The Zn-doped SPIONs exhibited the best resolution, while Mn-doped SPIONs showed the highest sensitivity. The overall MPI performance of all tracers was closely linked to their magnetic diameter and susceptibility, but deviated noticeably from the predictions of the Langevin model. Zn-doped SPIONs were encapsulated in a water-dispersible nanocarrier using flash nanoprecipitation (FNP), circumventing the need for citrate coating while preserving MPI performance. These findings show that the hydrodynamic size, size distribution, and composition of the SPIONs are critical to MPI performance and highlight the potential of combining FSP and FNP for large-scale production of the MPI tracers.