  Single phase cobalt ferrite (CoFe2O4, CFO) nanoparticles of a controlled size
(~ 6 nm) exhibiting superparamagnetic properties have been synthesized by
hydrothermal technique using oleic acid (OA) as surfactant. The oleic acid
coated CFO nanoparticles are stable in non-polar organic media, such as hexane
but are not well dispersible in water. The surface of these snanoparticles has
been further modified by citric acid using ligand exchange process, which makes
CFO nanoparticles more stable colloidal solution in water. Citric acid coated
CFO nanoparticles exhibits high dispersibility in water, high zeta potential,
very low coercivity and moderate saturation magnetization. Biocompatibility of
these CFO nanoparticles is demonstrated through cytotoxicity test in L929 cell
line.
