For decades, a link between increased levels of iron and areas of Alzheimer's disease (AD) pathology has been recognized, including AD lesions comprised of the peptide β-amyloid (Aβ). Despite many observations of this association, the relationship between Aβ and iron is poorly understood. Using X-ray microspectroscopy, X-ray absorption spectroscopy, electron microscopy and spectrophotometric iron(II) quantification techniques, we examine the interaction between Aβ(1–42) and synthetic iron(III), reminiscent of ferric iron stores in the brain. We report Aβ to be capable of accumulating iron(III) within amyloid aggregates, with this process resulting in Aβ-mediated reduction of iron(III) to a redox-active iron(II) phase. Additionally, we show that the presence of aluminium increases the reductive capacity of Aβ, enabling the redox cycling of the iron. These results demonstrate the ability of Aβ to accumulate iron, offering an explanation for previously observed local increases in iron concentration associated with AD lesions. Furthermore, the ability of iron to form redox-active iron phases from ferric precursors provides an origin both for the redox-active iron previously witnessed in AD tissue, and the increased levels of oxidative stress characteristic of AD. These interactions between Aβ and iron deliver valuable insights into the process of AD progression, which may ultimately provide targets for disease therapies.

The magnetic moments of magnetite nanoparticles are dramatically enhanced through the addition of zinc in a microbiologically driven synthesis procedure. The particles are produced through the reduction of Fe(III)‐compounds containing Zn(II) by the iron reducing bacterium Geobacter sulfurreducens. Results indicate a significant increase in the saturation magnetization by over 50% compared to magnetite at both room and low temperatures for relatively minor quantities of zinc substitution. A maximum saturation magnetization of nearly 100 emu g⁻¹ of sample is measured at room temperature. Analysis of the cation site ordering reveals a complex dependence on the Zn content, with the combined effect of Zn substitution of Fe³⁺ ions on tetrahedral sites, together with Fe²⁺ cation oxidation, leading to the observed magnetization enhancement for low Zn doping levels. The improved magnetic properties give superior performance in MRI applications with an MRI contrast enhancement among the largest values reported, being more than 5 times larger than a commercial contrast agent (Feridex) measured under identical conditions. The synthesis technique applied here involves an environmentally benign route and offers the potential to tune the magnetic properties of magnetic nanoparticles, with increased overall magnetization desirable for many different commercial applications.

The magnetic moment and anisotropy of magnetite nanoparticles can be optimised by doping with transition metal cations, enabling their properties to be tuned for different biomedical applications. In this study, we assessed the suitability of bacterially synthesized zinc- and cobalt-doped magnetite nanoparticles for biomedical applications. To do this we measured cellular viability and activity in primary human bone marrow-derived mesenchymal stem cells and human osteosarcoma-derived cells. Using AC susceptibility we studied doping induced changes in the magnetic response of the nanoparticles both as stable aqueous suspensions and when associated with cells. Our findings show that the magnetic response of the particles was altered after cellular interaction with a reduction in their mobility. In particular, the strongest AC susceptibility signal measured in vitro was from cells containing high-moment zinc-doped particles, whilst no signal was observed in cells containing the high-anisotropy cobalt-doped particles. For both particle types we found that the moderate dopant levels required for optimum magnetic properties did not alter their cytotoxicity or affect osteogenic differentiation of the stem cells. Thus, despite the known cytotoxicity of cobalt and zinc ions, these results suggest that iron oxide nanoparticles can be doped to sufficiently tailor their magnetic properties without compromising cellular biocompatibility.

Recent work has demonstrated increased levels of redox-active iron biominerals in Alzheimer’s disease (AD) tissue. However, the origin, nature, and role of iron in AD pathology remains unclear. Using X-ray absorption, X-ray microspectroscopy, and electron microscopy techniques, we examined interactions between the AD peptide β-amyloid (Aβ) and ferrihydrite, which is the ferric form taken when iron is stored in humans. We report that Aβ is capable of reducing ferrihydrite to a pure iron(II) mineral where antiferromagnetically ordered Fe²⁺ cations occupy two nonequivalent crystal symmetry sites. Examination of these iron(II) phases following air exposure revealed a material consistent with the iron(II)-rich mineral magnetite. These results demonstrate the capability of Aβ to induce the redox-active biominerals reported in AD tissue from natural iron precursors. Such interactions between Aβ and ferrihydrite shed light upon the processes of AD pathogenesis, while providing potential targets for future therapies.