We prepared Au/γ-Fe_2O_3 composite nanomaterials by sonochemically reducing Au(III) ions employing no stabilizer in the aqueous solution to form stable Au nanoparticles and allowing them to attach onto the surface of γ-Fe_2O_3 particles. Size of the formed Au nanoparticle depended on the initial concentration of Au(III) ions. The number of the Au nanoparticles, supported on each γ-Fe_2O_3 particle was controlled by changing the relative amounts of Au(III) ions and γ-Fe_2O_3 particles. The composite nanomaterials exhibited a high affinity with glutathione, a tripeptide with mercapto group so that separation and manipulation of glutathione in aqueous solutions could be performed by application of external magnetic field. Because the surfaces of the Au nanoparticles were not shielded by any stabilizers, or naked, sonochemically prepared Au/γ-Fe_2O_3 composite nanomaterials seemed to show stronger affinity to the glutathione than those by the radiochemical method.
