Magnetite nanoparticles (NPs) were synthesized by co-precipitating Fe2+ and Fe3+ in an ammonia solution. Magnetite NPs coated with 3-aminopropyltriethoxysilane (APTES) were prepared by silanization reaction. After activated with glutaraldehyde (GA), human serum albumin was covalently immobilized on these magnetic NPs. The influence of three different buffer solutions on covalent immobilization was studied. phosphate buffer saline solution (PBS) was shown the highest binding ability for immobilization process compared to other buffer solutions. The morphology and properties of these magnetic NPs were examined by transmission electron eicroscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and magnetization measurement. © 2009 Elsevier B.V. All rights reserved.