Chitosan-coated magnetic nanoparticles were prepared.At first

surface carboxyl functional magnetic nanoparticles (MNP-COOH) were prepared by co-precipitation.Secondly

chitosan molecules were adsorbed on the surface of particles by electrostatic interaction.The hydroxyl groups on the chitosan were then cross-linked by epichlorohydrin under the protection of primary amine groups with formaldehyde.After the amino-protecting agent were removed

the chitosan coated magnetic nanoparticles with primary amine groups on the surface were obtained.The magnetic nanopartieles were characterized by scanning electron microscopy (SEM)

X-ray diffraction (XRD)

Fourier transform infrared spectroscopy (FTIR)

thermogravimetric analysis (TGA)

vibrating sample magnetometry (VSM) and zeta potential analysis.The results showed that the magnetic nanoparticles were coated by chitosan successfully and could be completely dispersed in aqueous solutions of various pH=1~14 to form uniform sols.The magnetic cores of the paritcles are resistent to the corrosion of 0.1 mol/L HCl solution.The diameter of these nanoparticles with the saturation magnetization of 64.5 emu/g distributes between 10 and 20 nm.The remnant magnetization and coercivity of the nanoparticles were nearly zero

suggesting that it possessed a typical superparamagnetic characterization.The isotherm for the adsorption of BSA onto the MNP-CS surface was S-shaped.The maximum adsorption capacity reached 300 mg BSA/g MNP-CS.