Adjusting the Néel relaxation time of Fe <sub>3</sub> O <sub>4</sub> /Zn <i> <sub>x</sub> </i> Co <sub> 1− <i>x</i> </sub> Fe <sub>2</sub> O <sub>4</sub> core/shell nanoparticles for optimal heat generation in magnetic hyperthermia
Fernando Fabris, J. Lohr, Enio Lima, Adriele A. de Almeida, Horacio Troiani, Luis M. Rodríguez, Marcelo Vásquez Mansilla, Myriam H. Aguirre, Gerardo F. Goya, D. Rinaldi, Alberto Ghirri, Davide Peddis, D. Fiorani, Roberto D. Zysler, E. De Biasi, E. Winkler
Abstract
In this work it is shown a precise way to optimize the heat generation in high viscosity magnetic colloids, by adjusting the Néel relaxation time in core/shell bimagnetic nanoparticles, for Magnetic Fluid Hyperthermia applications. To pursue this goal, Fe3O4/ZnxCo1-xFe2O4 core/shell nanoparticles were synthesized with 8.5 nm mean core diameter, encapsulated in a shell of ~1.1 nm of thickness, where the Zn atomic ratio (Zn/(Zn+Co) at%) changes from 33 at% to 68 at%. The magnetic measurements are consistent with a rigid interface coupling between the core and shell phases, where the effective magnetic anisotropy systematically decreases when the Zn concentration increases, without a significant change of the saturation magnetization. Experiments of magnetic fluid hyperthermia of 0.1 wt% of these particles dispersed in water, DMEM (Dulbecco modified Eagles minimal essential medium) and a high viscosity butter oil, result in a large specific loss power (SLP), up to 150 W/g, when the experiments are performed at 571 kHz and 200 Oe. The SLP was optimized adjusting the shell composition, showing a maximum for intermediate Zn concentration. This study shows a way to maximize the heat generation in viscous media like cytosol, for those biomedical applications that requiere smaller particle sizes .