A Bioinspired Coprecipitation Method for the Controlled
Synthesis of Magnetite Nanoparticles
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Abstract
Nature often uses precursor phases
for the controlled development
of crystalline materials with well-defined morphologies and unusual
properties. Mimicking such a strategy in in vitro model systems would
potentially lead to the water-based, room-temperature synthesis of
superior materials. In the case of magnetite (Fe<sub>3</sub>O<sub>4</sub>), which in biology generally is formed through a ferrihydrite
precursor, such approaches have remained largely unexplored. Here
we report on a simple protocol that involves the slow coprecipitation
of Fe<sup>III</sup>/Fe<sup>II</sup> salts through ammonia diffusion,
during which ferrihydrite precipitates first at low pH values and
is converted to magnetite at high pH values. Direct coprecipitation
often leads to small crystals with superparamagnetic properties. Conversely,
in this approach, the crystallization kineticsand thereby
the resulting crystal sizescan be controlled through the NH<sub>3</sub> influx and the Fe concentration, which results in single
crystals with sizes well in the ferrimagnetic domain. Moreover, this
strategy provides a convenient platform for the screening of organic
additives as nucleation and growth controllers, which we demonstrate
for the biologically derived M6A peptide