Shape-Orchestrated Soft-Hard-Tandem Tracers: A Magnetic Control Strategy for Advanced Magnetic Particle Imaging

Magnetic particle imaging (MPI) is a promising diagnostic technology. However, its widespread adoption is hindered by suboptimal tracer performance, largely owing to limitations in nanoparticle design. To address these challenges, we developed a novel class of shape-orchestrated octahedral iron oxide nanoparticles (O-IONPs) using an innovative soft-hard-tandem (SHT) magnetic optimization strategy. This approach significantly enhances magnetic properties by suppressing surface spin disorder and fine-tuning surface magnetic anisotropy, yielding exceptional saturation magnetization (M_s = 101.06 ± 2.40 emu/g) alongside minimal coercivity (H_c < 2 Oe). As a result, our O-IONP tracer exhibited outstanding MPI performance, generating a 5.3-fold signal enhancement over the commercial tracer Vivo Trax at equivalent Fe doses while achieving submillimeter resolution (1.0 mm) and a detection limit of 24 ng Fe. Furthermore, by coating the nanoparticles with 4T1-macrophage hybrid cell membranes, we amplified in vivo MPI signals by 76.4-fold, yielding performance comparable to that of Vivo Trax with just a 60 μg intratumoral injection. This study bridges the gap between theoretical predictions and practical MPI applications by unlocking the full diagnostic potential of MPI using the SHT strategy.