Magnetic resonance of a dextran-coated magnetic fluid intravenously administered in mice

Magnetic resonance was used to investigate the kinetic disposition of magne tite nanoparticles (9.4 nm core diameter) from the blood circulation after intravenous injection of magnetite-based dextran-coated magnetic fluid in f emale Swiss mice. In the first 60 min the time-decay of the nanoparticle co ncentration in the blood circulation follows the one-exponential (one-compa rtment) model with a half-life of (6.9 +/- 0.7) min. The X-band spectra sho w a broad single line at g approximate to 2, typical of nanomagnetic partic les suspended in a nonmagnetic matrix. The resonance field shifts toward hi gher values as the particle concentration reduces, following two distinct r egimes. At the higher concentration regime (above 10(14) cm(-3)) the partic le-particle interaction responds for the nonlinear behavior, while at the l ower concentration regime (below 10(14) cm(-3)) the particle-particle inter action is ruled out and the system recovers the linearity due to the demagn etizing field effect alone.