Heating ability of cobalt ferrite nanoparticles showing dynamic and interaction effects.

The heating ability of magnetic nanoparticles (MNPs) intended for magnetic hyperthermia is quantified by means of the specific absorption rate (SAR), also referred to as specific loss power. This quantification is mainly performed on ferrofluids, even though the SAR values so obtained are often not representative of the nanoparticle performance inside tissues (solid matrices). In this study, the SAR of cobalt ferrite MNPs with mean crystallite diameters of 5.5 nm and 7.4 nm, functionalized or not, and dispersed in liquid or solid media, was determined in the 180-300 K temperature range. Higher SAR values were systematically obtained for samples in liquid media. On the one hand, heat capacity data together with zero-field-cooled and field-cooled magnetization curves allowed correlation of these results with ferrofluid dynamics originating from viscosity changes in samples dispersed in diethylene glycol. On the other hand, the higher degree of agglomeration attained by the functionalized MNPs after immobilization in paraffin wax seemed responsible for the decrease in SAR values and the shift in blocking temperature. In sum, MNP’s spatial arrangements acquired after ferrofluid injection in magnetic hyperthermia should be taken into account to predict SAR values during therapies.