A Bioinspired Coprecipitation Method for the Controlled\nSynthesis of Magnetite Nanoparticles

Abstract

Nature often uses precursor phases\nfor the controlled development\nof crystalline materials with well-defined morphologies and unusual\nproperties. Mimicking such a strategy in in vitro model systems would\npotentially lead to the water-based, room-temperature synthesis of\nsuperior materials. In the case of magnetite (Fe₃O₄), which in biology generally is formed through a ferrihydrite\nprecursor, such approaches have remained largely unexplored. Here\nwe report on a simple protocol that involves the slow coprecipitation\nof Fe^III/Fe^II salts through ammonia diffusion,\nduring which ferrihydrite precipitates first at low pH values and\nis converted to magnetite at high pH values. Direct coprecipitation\noften leads to small crystals with superparamagnetic properties. Conversely,\nin this approach, the crystallization kineticsand thereby\nthe resulting crystal sizescan be controlled through the NH₃ influx and the Fe concentration, which results in single\ncrystals with sizes well in the ferrimagnetic domain. Moreover, this\nstrategy provides a convenient platform for the screening of organic\nadditives as nucleation and growth controllers, which we demonstrate\nfor the biologically derived M6A peptide.