Understanding the influence of Gd deposition on the MPI and MRI performance of Fe₃O₄ nanoparticles for multimodal imaging applications

Fe₃O₄ core Gd shell nanoparticles are interesting candidates as multimodal MRI/MPI contrast agents/tracers that can potentially provide MPI signal from the magnetic iron component while still achieving positive MRI contrast from the Gd shell. However, a current challenge in synthesizing these NPs is controlling the uniformity of the Gd shell while maintaining the particle size. In this study, we show that by using thermal decomposition of mixed metal oleate precursors, the iron oxide nanoparticle core with Gd shell coating can be varied from 7% to 27% while maintaining a high level of control over the particle size, producing highly uniform particles of d = 13.5 nm. Iron oxide nanoparticles with moderate Gd coating have resulted in improved MPI signal and MRI relaxation compared with commercial tracers, indicating that iron oxide core Gd shell nanoparticles are effective materials for both MPI and MRI applications. These results demonstrate the ability to synthetically control both the amount of the Gd shell and the size of the core-shell iron oxide nanoparticles, which can be applied to other magnetic nanomaterials.