The effect of field parameters, nanoparticle properties and immobilization on the specific heating power in magnetic particle hyperthermia

Magnetic nanoparticles ( MNP) are intended for utilization in cancer therapy as they produce damaging heat in the presence of AC magnetic fields. In order to reach the required temperature with minimum particle concentration in tissue the specific heating power ( SHP) of MNP should be as high as possible. The aim was to clarify the influence of magnetic field parameters and nanoparticle properties on the SHP. As usual ferrofluids exhibit broad size distributions, a magnetic fractionation of a commercial iron oxide nanoparticle suspension was performed in order to obtain particles with varying properties. The fractions obtained were characterized by means of atomic force microscopy and magnetometry, among other techniques. Frequency spectra of the susceptibility show clear peaks at low frequencies related to the Brown relaxation. This effect vanishes after particle immobilization. Theoretical spectra considering experimentally determined size distributions are in agreement with experimental data. The SHP derived from AC susceptometry is in accordance with that directly determined by calorimetry. A maximum SHP of 160 W g(-1) (400 kHz, 8 kA m(-1)) was detected for the largest particles, showing a behaviour in the transitional regime between superparamagnetic and stable ferromagnetic.