Radio-Frequency Heat Generation in Magnetic Nanoparticles: Influence of Particle Size

E. LIMA JR.; R.D. ZYSLER; A. D. ARELARO; H.R. RECHENBERG; L.M. ROSSI; G.F. GOYA; T. TORRES; C. MAQUINA; M.R. IBARRA

Buenos Aires

Congreso; At the Frontiers of Condensed Matter IV: Current trends and novel materials FCM 08; 2008

The study of magnetic nanoparticles (MNPs) as heating agents in oncology protocols has attracted considerable attention in recent years. Magnetic hyperthermia consists in increasing the temperature of the tumor through alternating magnetic field acting on MNPs previously incorporated in that tissue. Nanoparticles are promising agents to increase the effectiveness of the heating process and the control of the affected area to avoid damage in the healthy tissues. In fact, Magnetic hyperthermia based in MNPs is already used in testing protocols as complementary technique of radiotherapy and chemotherapy in the treatment of breast and cerebral tumors, but the optimization of the absorption mechanism of ac power by the mono-multidomain MNPs and the delivering of the absorbed power to the living tissues are still open questions. In the present work, we have performed the systematic study of the Fe3O4 MNPs with controlled size from 3 to 25 nm, in order to determine the relevant parameters involved in the absorption power. Samples were prepared by decomposition of Fe(acac)3 at high temperature (265 °C or 640 ºC) in the presence of a long-chain alcohol and surfactants, producing well-crystalline MNPs with narrow grain size distribution (diameter distribution width as good as 0.13) covered by a organic layer (oleic acid), avoiding agglomeration and increasing the chemical stability of the particles. Morphological and magnetic characterizations were performed by TEM and experiments in a SQUID magnetometer. Absorption power (SPA) was measured in a commercial ac applicator with f = 250 kHz and field amplitude of 20 mT (model DM100 by nB nanoscale Biomagnetics). According to our results, there is a straight correlation between the power absorption and the grains size of the particle, with an optimum diameter of <d> ~ 17 nm for absorption (350 W/g of Fe3O4 MNPs). This result was explained in terms of a model considering Néel and Brown relaxation mechanisms. Superficial chemistry of the particle was also changed to increase the biocompatibility of the systems.