Same magnetic nanoparticles, different heating behavior: Influence of the arrangement and dispersive medium

• We synthetize a series of Fe3O4 nanoparticles by the seeded-growth method.
• We characterize the heating ability of 13.9 nm particles dispersed in several media.
• We apply SAR(T) characterization to locate the onset of superparamagnetic behavior.
• The highest SAR values are obtained in low-concentration solid-alkane dispersion.
• Acquired arrangements in different media strongly modify SAR trends and values.

The heating ability of the same magnetic nanoparticles (MNPs) dispersed in different media has been studied in the 170–310 K temperature range. For this purpose, the biggest non-twinned nanoparticles have been selected among a series of magnetite nanoparticles of increasing sizes synthesized via a seeded growth method. The sample with nanoparticles dispersed in n-tetracosane, thermally quenched from 100 °C and solid in the whole measuring range, follows the linear response theoretical behavior for non-interacting nanoparticles, and displays a remarkably large maximum specific absorption rate (SAR) value comparable to that of magnetosomes at the alternating magnetic fields used in the measurements. The other samples, with nanoparticles dispersed either in alkane solvents of sub-ambient melting temperatures or in epoxy resin, display different thermal behaviors and maximum SAR values ranging between 11 and 65% of that achieved for the sample with n-tetracosane as dispersive medium. These results highlight the importance of the MNPs environment and arrangement to maintain optimal SAR values, and may help to understand the disparity sometimes found between MNPs heating performance measured in a ferrofluid and after injection in an animal model, where MNP arrangement and environment are not the same.