Genetically engineered bacterial magnetosomes as optimized tracers for magnetic particle imaging

Medical imaging relies on tracer materials to enable accurate visualization and diagnosis of diseases. Magnetic Particle Imaging (MPI) is an innovative tomographic modality that offers exceptional sensitivity and temporal resolution. These characteristics make MPI particularly promising for clinical applications such as real-time vascular and perfusion imaging, tumor detection, and intraoperative guidance. However, MPI performance has so far been limited by the quality of available tracers, as conventional chemical synthesis provides only restricted control over the size, shape, and magnetic properties of iron oxide nanoparticles. Biogenic magnetic nanoparticles, so-called magnetosomes, produced by magnetotactic bacteria, represent a compelling alternative. Magnetosome biosynthesis is fully genetically encoded, enabling the natural formation of magnetite nanoparticles with uniform size and morphology, which is difficult to achieve through chemical synthesis. Moreover, genetic engineering of the bacterial production host allows precise tuning of particle characteristics, including size, shape, and magnetic behavior, to meet specific application requirements. In this study, magnetosomes isolated from different Magnetospirillum gryphiswaldense mutant strains, each biomineralizing particles with distinct core diameters, were systematically evaluated as potential MPI tracers. Magnetic particle spectroscopy (MPS) was used to identify the most promising candidates based on their signal properties. These tracers were subsequently subjected to detailed signal analyses and phantom experiments to directly compare their imaging performance. Our findings demonstrate that genetically tailored magnetosomes can substantially improve MPI signal quality, underscoring their potential as next-generation tracers. This work provides a foundation for the rational design of optimized biogenic nanoparticles to advance preclinical and future clinical MPI applications. STATEMENT OF SIGNIFICANCE: Magnetic Particle Imaging (MPI) is a novel imaging technology with high sensitivity and real-time capabilities, making it highly promising for clinical applications such as blood flow monitoring and tumor detection. The performance of MPI strongly depends on the properties of the tracer materials used. However, producing high-quality tracers through conventional chemical synthesis remains challenging. In this study, we introduce an innovative biological approach by using genetically engineered magnetotactic bacteria to produce uniform magnetic nanoparticles, so-called magnetosomes. This strategy allows precise control of particle size, shape, and magnetic properties, resulting in tracers with superior performance. Our findings pave the way for the development of next-generation MPI tracers, advancing both fundamental research and potential clinical translation.