Magnetite/polypyrrole hybrid nanocomposites as a promising magnetic resonance imaging contrast material

摘要

We have prepared magnetite nanoparticles (Fe_3O_4-NPs) almost spherical in shape with average particle size of 10 nm and successfully encapsulated them in an envelope of polypyrrole (PPY) chains via an emulsion polymerization route using sodium dodecyl sulfate as surfactant. The resulting PPY-coated Fe_3O_4-NPs (Fe_3O_4-NPs/PPY) suspensions were stable with particles exhibiting a triangular prismatic morphology and an average diameter below 100 nm. In fact, all colloidal solutions were stable in aqueous media with typical ζ-surface potential values of -33.9 mV (Fe_3O_4-NPs) and -20.0 mV (Fe _3O_4-NPs/PPY). Although X-ray diffraction studies revealed the presence of a magnetic phase Fe_3O_4, the identified diffraction peaks are consistent with the presence of a spinel structure of magnetite. A ferromagnetic behavior, such as lower coercive force (H_c = 0.065 T), was observed for all magnetic nanoparticles examined. The ~1H NMR relaxation times T_1 and T_2 of selected Fe_3O_4-NPs/PPY samples were also measured and their relaxivities r_1 (1.1 s~(-1) mM~(-1)) and r _2 (61.9 s~(-1) mM~(-1)) compare favorably to those of contrast agents commercially used in human examinations. We suggest that the present results indicate that these hybrid nanocomposites are promising materials for the development of a platform of specialized contrast agents for ~1H Magnetic Resonance Imaging.