Relaxation of ferromagnetic nanoparticles in macrophages: In vitro and in vivo studies

Abstract The relaxation characteristics of magnetic nanoparticles (CoFe 2 O 4 ) were investigated in J774A.1 macrophages and after voluntary inhalation. In dry form 25% of the particles showed Neel relaxation. Relaxation in macrophages occurred within minutes and could be inhibited by fixation, showing Brownian relaxation and intracellular transport processes. Relaxation in the lung happened similarly, but was dependent on the time after deposition. The particles were cleared from the lung within 2 weeks.