Rod-like particles of silica-coated maghemite: Synthesis via akaganeite, characterization and biological properties

•Rod-like maghemite particles were prepared by using an akaganeite precursor.•The oxidation state of Fe was unambiguously determined by Mössbauer spectroscopy.•At least partial ordering of vacancies in the maghemite structure was evidenced.•The silica-coated product did not show any cytotoxicity up to 0.42 mmol(Fe)/L. A multistep procedure, employing akaganeite FeO(OH,Cl) as a precursor, was developed for the preparation of rod-like maghemite particles for medical applications. At first, akaganeite rods with length of several hundred nm and width of ≈85 nm were prepared under hydrothermal conditions and were subsequently coated with mesoporous silica. Such coating enabled to maintain the shape of rods during the following steps that involved structural transformation of akaganeite to maghemite, i. e. γ-Fe2O3. Then the original protective coating was removed by alkaline leaching, bare maghemite rods were isolated, and their structure and ferrimagnetic order were characterized by X-ray diffraction, TEM inspection, Mössbauer spectroscopy and SQUID magnetometry. The magnetization of the bare maghemite rods, that were formed by elongated clusters of ≈10–20 nm crystallites, made 47.0 and 41.7 Am2/kg in magnetic field of 3 T at 5 K and 300 K, respectively. The hysteresis loops of both the bare and coated products at 300 K and ZFC/FC studies showed that the maghemite particles were largely blocked at room temperature in spite of the small size of crystallites. Finally, the particles were equipped with standard silica coating for biological studies. An evaluation of cytotoxicity of this silica-coated product was performed on two cell lines, namely A549 and MCF-7. The viability of cells incubated with particles at the concentration of 0.10, 0.21 and 0.42 mmol(Fe)/L was determined after 24 h and 48 h of incubation, and the values normalized to the viability of negative control were generally higher than 95%. Moreover, the real-time monitoring of cell adhesion, proliferation, and cytotoxicity by an xCELLigence system during 72 h of the incubation with particles revealed only some decrease of the cell index for the MCF-7 cells at the high concentration.