Iron oxide magnetic nanoparticles for magnetic fluid hyperthermia therapy: synthesis and characterization

During recent years, an increased interest in magnetic nanoparticles (NPs) for their use in biomedical applications, in particular for hyperthermia therapy, has been observed [1]. This promoted the research on synthesis routes that allow better control in NPs shape and size, and, due to the need of obtaining bio-compatible NPs, NPs stabilization in aqueous media. In this study, we synthesized iron oxide magnetic nanoparticles in presence of 2-pyrrolidone, as that acts both as surfactant and solvent [2] and permits to disperse the synthesized nanoparticles in water without any further functionalization. The magnetic NPs were synthesized by thermal decomposition of iron chloride (III) hexahydrate (FeCl3∙6H2O) in presence of 2-pyrrolidone; the reagents relative concentration was changed so to access the effect of that on the morphology and on the magnetic properties of the NPs. After the synthesis, the NPs were precipitated and dried, and then dispersed in deionized water with a 10 mg per 1 ml concentration. The magnetic properties of the NPs were investigated using a superconductive quantum interference device (SQUID) magnetometer; Mössbauer spectroscopy measurements were performed in the 4 K – 300 K range. Size and morphology of the particles were investigated with a transmission electron microscope (TEM), while the heating rate of the magnetic liquids was measured using an inductor suitably designed to maximize the magnetic field uniformity [3]. The sample with the smallest chloride concentration shows nanoparticles with a fine dispersion (NP size ~ 5 nm); an increase in chloride concentration produces flower-shaped NPs, as those presented in fig. 1, where fine nanoparticles are aggregated so to form “flowers” with an average size of 20 nm. A further increase in chloride concentration produces again a fine dispersion of magnetic NPs. The magnetic fluid with flower-shaped NPs turns out to be the most interesting for hyperthermia, as it produces the highest heating rate; the combination of SQUID and Mössbauer characterization reveals the strong influence of magnetic dipolar interactions on sample magnetic behaviour. From 300 K down to 50 K the Mössbauer spectra display just a doublet contribution, whose width increases as temperature decreases, possibly due to superparamagnetic relaxation effects; just below 50 K a broad sextet appears. This may suggest that the fine nanoparticles in flower-shaped aggregates behave as single entities, interacting via dipolar and not exchange interactions. Finally, cell culture experiments will be also presented, as NPs have been added to a cell culture in order to evaluate cellular uptake. In particular, TEM analyses revealed a time-dependent uptake of flower-shaped NPs by breast cancer cells. References [1] A. Akbarzadeh et al., Nanoscale Research Letters 7 (2012) 144. [2] A. K. M. Krishnan, IEEE Trans. On Magnetics, 46 (2010) 2523. [3] P. Di Barba et al., IEEE Trans. On Magnetics 46 (2010) 2931.