Environmental oxidative aging of iron oxide nanoparticles

The environmental aging of functional iron oxide nanomaterials, especially those used in biomedical applications, may have significant consequences for both their mechanism of action and their safety profile. However, to date, there has been no way to systematically measure this property, and the problem has been largely overlooked. We show here that a recently proposed “center of gravity” method for determining the composition of magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) mixtures via ⁵⁷Fe Mössbauer spectroscopy can be applied to the matter. We show that a long-established diffusion model can be used to characterize the oxidative aging process, yielding a parametric (and therefore predictive) description of the magnetite-to-maghemite oxidation processes occurring within the nanoparticles.