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Using the electrochemical route, cobalt ferrite nanoparticles (NPs) with two different sizes were synthesized and stabilized in water by coating with citric acid. The specific absorption rate (SAR) values of aqueous suspensions of magnetic nanoparticles with crystal sizes of 13 and 28 nm were investigated in the frequency range 32−101 kHz and up to 51 mT. SAR values were higher for the larger NPs and reached 133 W/g. Numerical simulations are used for a quantitative analysis of hyperthermia experiments and seem to indicate that the larger NPs are multidomain. Cytotoxicity analysis was also performed in HeLa tumor cells; a null cytotoxicity of these nanoparticles in cell tissues were obtained.

Summary• The analysis of metal distribution in Imperata cylindrica , a perennial grass isolated from the banks of Tinto River (Iberian Pyritic Belt), an extreme acidic environment with high content in metals, has shown a remarkable accumulation of iron. This property has been used to study iron speciation and its distribution among different tissues and structures of the plant.• Mössbauer (MS) and X-ray diffraction (XRD) were used to determine the iron species, scanning electron microscopy (SEM) to locate iron biominerals among plant tissue structures, and energy-dispersive X-ray microanalysis (EDAX), X-ray fluorescence (TXRF) and inductively coupled plasma emission spectroscopy (ICP-MS) to confirm their elemental composition.• The MS spectral analysis indicated that iron accumulated in this plant mainly as jarosite and ferritin. The presence of jarosite was confirmed by XRD and the distribution of both minerals in structures of different tissues was ascertained by SEM-EDAX analysis.• The convergent results obtained by complementary techniques suggest a complex iron management system in I. cylindrica , probably as a consequence of the environmental conditions of its habitat.

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