Surfactant free superparamagnetic iron oxide nanoparticles for stable ferrofluids in physiological solutions

A process is reported to obtain a nanoparticle sol from co-precipitated iron oxide particles without using any surfactant. The sol - a true ferrofluid - is not only stable over a wide range of pH but also in physiological solutions. This is a decisive step towards biomedical applications where nanoparticle agglomeration could so far only be prevented by using unwanted surfactants. Ferrofluids of superparamagnetic Fe 3 O 4 nanoparticles with "patchy" silica shell are stable over a wide pH range and in physiological solutions.