Ferrofluids have a wide application potential in the field of biomedicine, including cellular manipulation and sorting, hyperthermia and targeted drug delivery. For such applications to be practical, the colloidal suspension of magnetic nanoparticles within a ferrofluid needs to be stable under physiological conditions. Current approaches that utilize non-specific adsorption of surfactants onto nanoparticle surfaces do not provide stability against agglomeration under dilution or increased ionic strength. Here, we present a new approach to synthesizing water-based and bio-compatible ferrofluids using genetically engineered peptides for inorganics (GEPI's) that are selected for specific and strong binding to the surface of the nanoparticles. Initial results demonstrate the efficacy of GEPI's in significantly reducing agglomeration with increasing ionic strength when used in a ferrofluid comprised of cobalt-ferrite nanoparticles surrounded with a thin silica shell. The same approach could easily allow direct biological functionalization of the nanoparticles, rendering such ferrofluids useful in a wide range of applications.
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