Biocompatible and high-magnetically responsive iron oxide nanoparticles for protein loading

Superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized in this work, featuring uncommonly high magnetization saturation values at room temperature for coated nanoparticles. They also show very low cytotoxicity and promising protein loading efficacy. The ratios of iron(III) acetylacetonate (precursor), benzyl ether (solvent) and oleylamine (surfactant) were changed relatively to those used in the thermal decomposition protocols reported in the literature, in order to enhance the magnetic response of the nanoparticles to an external magnet. The SPIONs were fully characterized in terms of their chemical composition, iron oxide phases, grain/particle sizes and magnetic behaviour. They are predominantly constituted by magnetite, with minor maghemite contributions, as observed by Mössbauer spectroscopy and X-ray diffraction data. The magnetization saturation at room temperature of the best SPIONs achieved 68 emu g−1, which is relevant considering that it corresponds to ∼10 nm sized nanoparticles, where interactions have some significance. This characteristic is mainly due to the high content of magnetite (93% of iron sites) in the nanoparticles and low aggregation provided by their organic coating. In addition, Field-Cooled and Zero Field-Cooled curves allowed to confirm, from the blocking and irreversibility temperatures, the nanoparticle size distribution broadening obtained by Transmission Electron Microscopy.