Heat Generation by Magnetic Losses of Fe3O4 Nanoparticles for Magnetic Fluid Hyperthermia

M. VASQUEZ MANSILLA; E. LIMA JR.; E. DE BIASI; M. L. MOJICA PISCIOTTI; H.E. TROIANI; F. EFFENBERG; L.M. ROSSI; R.D. ZYSLER

Roma

Congreso; X International Conference on Nanostructured Materials – NANO2010; 2010

ISM-CNR

In Magnetic Fluid Hyperthermia (MFH) therapy the energy absorption by nanoparticles in the presence of an alternating magnetic field increases locally the temperature of a targeting tissue. Basically, the mechanisms for magnetic losses in superparamagnetic nanoparticles are the thermal relaxation of their magnetic moments (Néel relaxation and Brown relaxation). Instead, the hysteresis losses are frequently negligible. Concerning the thermal relaxation mechanisms, the absorption will depends of the size, magnetic anisotropy, hydrodynamic radius, and magnetic interactions. In the present work, we show results on the Specific Absorption Rate (SAR) measurements of Fe3O4 nanoparticles produced by thermal decomposition of Fe(acac)3 in the presence of surfactants and dispersed in an organic solvent. We have studied the effects of diameter, grain size distribution, crystallinity, and agglomeration on the heat capability of Fe3O4 nanoparticles. Two sets of samples were growth in successive synthesis procedure using smaller particles as seeds. In the first set, we have monodispersed and non-interacting nanoparticles, while in the second one we observe agglomerated nanoparticles large hydrodynamic ratio) with wider grain size distribution. Heat conversion mechanism based in the Stoner-Wohlfarth hysteresis losses must to be added to the Néel-Brown relaxation to explain our experimental data. In the former mechanism, the heating ability of a monodomain nanoparticle can be calculated considering the dependence of the remanence and coercive field with the frequency and amplitude of the alternating applied field. The results and discussion presented herein will allow us to optimize the SAR conditions aiming to the use of this nanometric system in MFH protocols. We have observed a maximum value of Specific Absorption Rate (SAR) as high as 50 W/g applying an ac magnetic field of 100 kHz and 160 Oe.