Tuning Surface Coatings of Optimized Magnetite Nanoparticle Tracers for in vivo Magnetic Particle Imaging

Surface coatings are important components of magnetic particle imaging (MPI) tracers—they preserve their key properties responsible for optimum tracer performance in physiological environments. In vivo , surface coatings form a physical barrier between the hydrophobic superparamagnetic iron oxide nanoparticles (SPION) cores and the physiological environment, and their design dictates the blood half-life and biodistribution of MPI tracers. Here, we show the effect of tuning poly(ethylene glycol) (PEG)-based surface coatings on both in vitro and in vivo (mouse model) MPI performance of SPIONs. Our results showed that varying PEG molecular weight had a profound impact on colloidal stability, characterized using dynamic light scattering, and the m ′( H ) response of SPIONs, measured in a 25 kHz/20 mT/µ − 0 1 max magnetic particle spectrometer. Increasing PEG molecular weight from 5 to 20 kDa preserved colloidal stability and m ′( H ) response of ~25 nm SPIONs—the optimum core diameter for MPI—in serum-rich cell culture medium for up to 24 h. Furthermore, we compared the in vivo circulation time of SPIONs as a function of hydrodynamic diameter and showed that clustered SPIONs can adversely affect blood half-life; critically, SPIONs with clusters had five times shorter blood half-life than individually coated SPIONs. We anticipate that the development of MPI SPION tracers with long blood half-lives have potential not only in vascular imaging applications, but also enable opportunities in molecular targeting and imaging—a critical step toward early cancer detection using the new MPI modality.