Magnetite nanoparticles with high heating efficiencies for application in the hyperthermia of cancer

Magnetic hyperthermia is a safe method for cancer therapy. A gap-type alternating current magnetic field (100 kHz, 100-300 Oe) is expected to be clinically applicable for magnetic hyperthermia. In this study, magnetite nanoparticles (MNPs) varying in size from 8 to 413 nm were synthesized using a chemical coprecipitation and an oxidation precipitation method to find the optimum particle size that shows a high heating efficiency in an applied magnetic field. The particles' in vitro heating efficiency in an agar phantom at an MNP concentration of 58 mg Fe/ml was measured in an applied magnetic field. In a magnetic field of 120 Oe, the temperature increase (AT) of the agar phantom within 30 s was 9.3 degrees C for MNPs with a size of 8 nm, but was less for the other samples, while in a magnetic field of 300 Oe, Delta T = 55 degrees C for MNPs with a size of 24 nm, and Delta T = 25 degrees C for MNPs with a size of 8 nm. The excellent heating efficiency of MNPs with a size of 24 nm in a magnetic field of 300 Oe may be due to a combination of the effects of both relaxation and hysteresis losses of the magnetic particles. It is believed that MNPs with a size of 8-24 nm will be useful for the in situ hyperthermia treatment of cancer. (C) 2010 Elsevier B.V. All rights reserved.