A block copolymer-stabilized co-precipitation approach to magnetic iron oxide nanoparticles for potential use as MRI contrast agents

A library of magnetic nanoparticles was generated using in situ co-precipitation of ferrous (Fe2+) and ferric (Fe3+) ions from aqueous solutions in the presence of functional block copolymers. Three different iron oxide anchoring groups, viz., phosphonic acid, carboxylic acid or glycerol were incorporated into well-defined diblock copolymers of poly(oligoethylene glycol acrylate) employed to stabilize the iron oxide nanoparticles. The [copolymer] : [Fe] ratio was varied to wield control over nanoparticle diameters within the range of 7-20 nm. The relationship between colloidal stability and nanoparticle crystallinity was investigated using dynamic light scattering, transmission electron microscopy and X-ray diffraction measurements. The amount of polymer employed during the co-precipitation proved critical in governing crystallinity and colloidal stability. We report a correlation between the polymer grafting density and the chemical structure of the anchoring group. Finally, the transverse relaxivity of the iron oxide nanoparticles in water, was investigated using a 9.4T magnetic resonance imaging scanner yielding values varying from 70 to 370 mM(-1) s(-1).