γ-Fe₂O₃ nanoparticles about 30 nm were prepared using chemical co-precipitation firstly, and then they are modified with thiol group by means of 3-mercaptopropyltriethoxysilane (MPTES), γ-Fe₂O₃@Au nanoparticles with size of 35.9 nm were obtained. XRD, TEM, UV, FT-IR and VSM analysis showed the surface appearance, size, structure, optical and magnetics property of the gold coated magnetic nanoparticles (γ-Fe₂O₃@Au). The result showed that Au was coated on the surface of γ-Fe₂O₃ successfully, the obtained γ-Fe₂O₃@Au composite nanoparticles are superparamagnetic, streptavidin was modified on the surface of γ-Fe₂O₃@Au nanoparticles effectively. The fluorescent signal before and after adsorption of Cy3 labeled oligonucleotide showed that the streptavidin modified γ-Fe₂O₃@Au nanoparticles had good biological activity and without fluorescence background. Most kinds of biological molecular can be combined on the surface of the streptavidin modified γ-Fe₂O₃@Au nanoparticles through biotin-streptavidin system. Being able to be separated with magnetic field easily, they have great potential application prospects.

Key words: MPTES (3-Mercaptopropyltriethoxysilane), γ-Fe₂O₃@Au composites, streptavidin, biological application, bioelectronics