Confirmation of highly stable 10 nm sized Fe3O4 nanoparticle formation at room temperature and understanding of heat-generation under AC magnetic fields for potential application in hyperthermia

Iron oxide nanoparticles such as magnetite (Fe3O4) and maghemite (gamma -Fe2O3) have been used in biological applications due to their high biocompatibility, i.e., as a contrast agent in magnetic resonance imaging, a hyperthermia agent in cancer treatment, a drug carrier, etc. There are debates on the formation of Fe3O4 or gamma -Fe2O3 from the different synthesis routes including the co-precipitation method as the bulk size of the particle decreases to nanometers. This study reports on the preparation of pure 10 nm sized Fe3O4 nanoparticles at room temperature so that this can be kept for a long time (a few years) in an inert environment; otherwise, the surface of the Fe3O4 particles gets oxidized and, partly, gets converted into undesirable compounds of iron oxides such as alpha -Fe2O3 and Fe(OH)(3). The formation of Fe3O4 has been ascertained by thermogravimetric analysis, the color of the compound, x-ray photoelectron spectroscopy, and magnetic measurement. It shows the contribution of hysteresis loss, eddy current, and Neel's and Brownian relaxations in heat-generation by applying different alternating current magnetic fields. Power loss follows H-2 dependence. Heat generation of Fe3O4 magnetic nanoparticles in phosphate buffer saline will be the potential candidate of the therapy of cancer.