Synthesis of composite nanoparticle material of gold and magnetic iron oxide by gamma-ray irradiation

A composite nanoparticle material was synthesized by gamma-ray irradiation of an aqueous solution containing gold ions and dispersing iron-oxide nanoparticles. Gamma-ray irradiation induces reduction of gold ions in the solution to form metallic gold, which are stabilized at the surface of iron-oxide particles. TEM observation indicated that many gold grains of 5 nm surround each iron oxide particle. A reddish color due to the surface plasmon resonance of nano-sized gold was seen in an aqueous dispersion of the composite particles and attracted by a magnet, which indicates a connection of gold and iron-oxide in the nanoscale. The surface of gold in the composite particles was found reactive with the mercapto group and to adsorb glutathione and two amino acids possessing sulfur preferably out of seventeen amino acids. The iron oxide surface was substantially covered up with gold grains grown from the seed grains initially deposited by the gamma-rays. The synthesis procedure, characterization, and the tests of the molecule adsorption are described.