New work looks to understand how iron oxide nanoparticles age, and how aging may change their functional or safety profiles. By combining lab-based Mössbauer spectroscopy with 'center of gravity' analysis, researchers can quantify the diffusive oxidation of magnetite into maghemite, and track the process. The work is poised to help understand the aging mechanisms in nanomaterials, and how these effects change the way they interact with the human body.