Comparative Study of Surfactant-Coated Ferromagnetic Nanoparticles for Hyperthermia Application

Sub-single-magnetic-domain γ-Fe₂O₃ and Fe­₃O₄ nanoparticles (5 to 16 nm diameter) with surfactant coatings were prepared via high energy ball-milling of commercial powders. Such superparamagnetic particles have application to hyperthermia cancer treatment, where particles release EM radiation in the form of heat when exposed to an alternating magnetic field.  The samples were milled (SPEX 8000M Mixer/Mill) in a tungsten-carbide container which held hexane as a carrier liquid along with proportionate amounts of oleic acid surfactant for the environment.  TEM micrographs revealed spherical particle morphology and the effect of the oleic acid shell formed around the particles. Milling times of 3, 6, 9, and 12 hours with mass ratios (oleic acid):(γ-Fe₂O₃) of 0:1, 1:5, 1:10 and 1:20 were used. 

Samples of γ-Fe₂O₃ and Fe­₃O₄ nanoparticles were compared using morphological, magnetic, and thermal emissivity properties. Optimal particle size distributions were obtained for 6 to 9 milling hours for both substances, and a 1:10 oleic acid to γ-Fe₂O₃ mass ratio but 1:20 oleic acid to Fe₃O₄ mass ratio.  At room temperature, a reduced internal magnetic field (~480 kOe) was recorded via Mössbauer Spectroscopy compared to bulk γ-Fe₂O₃ (~500 kOe), due to magnetic relaxation effects; similar results were concluded for Fe₃O₄ particles. Magnetization measurements beginning T=2K for a field of 200 Oe were performed using a Vibrating Sample Magnetometer on VersaLab equipment by Quantum Design in order to show the hysteretic loop of γ-Fe₂O₃ and Fe­₃O₄ nanoparticles milled with 20% oleic acid by mass content. Ferrofluid stability was examined via particle hydrodynamic radius measurements and thermal transport characteristics were determined via Specific Absorption Rate (SAR) measurements upon nanoparticle exposure to alternating magnetic fields (a frequency of 282 kHz). With decreasing particle size, data showed a strong, but saturating temperature in the carrier liquid under alternating field for Fe₃O₄ (70 °C). We observed a peak SAR value for the 10% oleic acid content in the Fe­₃O₄ particles at 7.638 W/g. Such saturation was not reached in the case of γ-Fe₂O₃, where more milling time resulted in larger SAR (4.607 W/g for 20% oleic acid content) and the temperature of the carrier liquid readily increased with time under the alternating magnetic field.

In general, analysis indicated magnetite particles as being more apt for hyperthermia cancer treatment. I would like to acknowledge my faculty collaborators: Dr. Arthur Viescas (Villanova, Physics), Dr. Calvin H. Li (Villanova, Mechanical Engineering), Dr. Steven May (Drexel, Materials Science and Engineering), and my adviser Dr. Georgia C. Papaefthymiou (Villanova, Physics), for their guidance in this study.