A universal magnetic ferrofluid: Nanomagnetite stable hydrosol with no added dispersants and at neutral pH.

A facile method to produce highly stable magnetite magnetic fluid at neutral pH without any stabilizing agents, resulting in pure Fe3O4 nanoparticles dispersed in water is described. The hydrosol which consists of only two components - magnetite and water - behaves as a typical ferrofluid, that is, although it responds to a magnetic field, the magnetic particles cannot be phase-separated from the water by that field. No such pure magnetic fluid have been described before, making it a universal carrier which can be easily modified for any application in materials science and chemistry, and in particular for a range of applications where non-corrosivity, low viscosity, and mild conditions are needed, such as in most bioapplications and in nano electro-mechanical systems. Under optimal conditions the hydrosol is stable for at least three months.