Development of long circulating magnetic particle imaging tracers: use of novel magnetic nanoparticles and entrapment into human erythrocytes.

Magnetic particle imaging (MPI) is highly promising for biomedical applications, but optimal tracers for MPI, namely superparamagnetic iron oxide-based contrast agents, are still lacking. The encapsulation of commercially available nanoparticles, specifically synomag-D and perimag, into human red blood cells (RBCs) was performed by a hypotonic dialysis and isotonic resealing procedure. The amounts of superparamagnetic iron oxide incorporated into RBCs were determined by Fe quantification using nuclear magnetic resonance and magnetic particle spectroscopy. Perimag-COOH nanoparticles were identified as the best nanomaterial for encapsulation in RBCs. Perimag-COOH-loaded RBCs proved to be viable cells showing a good magnetic particle spectroscopy performance, while the magnetic signal of synomag-D-COOH-loaded RBCs dropped sharply. Perimag-COOH-loaded RBCs could be a potential tool for MPI diagnostic applications.