Energy absorption of superparamagnetic iron oxide nanoparticles by microwave irradiation

The main complexity in hyperthermia is generating and controlling the temperature distribution within tumor cells without damaging the normal tissue. Superparamagnetic iron oxide nanoparticles (SPIONs) with a diameter of 11 nm were prepared by controlled coprecipitation and coated with oleic acid to prevent agglomeration and flocculation in the solvent. In situ monitoring of the temperature increment was performed to interpret the microwave absorption rate of the SPION dispersed in appropriate host media (polar or nonpolar solvents) during microwave irradiation. This approach allowed for the prediction of heating mechanisms as a result of the excitation of unpaired electrons of iron, effects of coating agents, particle size, and volume fraction (φ). The conversion efficiency from microwave irradiation to thermal energy was predicted by applying the conservation of energy to a differential volume. The rates of heat loss and energy absorption were obtained by nonlinear fitting of the experimental data.