Magnetic nanoparticles were modified by polyasparticate and poly(ethyleneimine) via layer-by-layer self-assembly. The zeta-potential and protein adsorption of the modified magnetic nanoparticles (Fe₃O₄) were studied. Magnetic nanoparticles were synthesized by chemical co-precipitation method and then were modified via layer-by-layer self-assembly. The size of the particles was examined by transmission electron microscopy (TEM). Fourier transform infrared (FTIR) measurement was used to confirm the change of composition on the surface of nanopartilces. The effect of modification on the zeta potential of nanoparticles was disscused. The zeta potential of nanoparticles was related to electric property of molecules on the surface of magnetic nanopartilces. The isoelectric point of magnetic nanoparticles is closely neutral. The zeta potential of polyasparticate-modified magnetic nanoparticles is negative. The isoelectric point of poly(ethyleneimine)-modified magnetic nanoparticles decreased with decreasing pH of PEI solution. The isoelectric point of the modified magnetic nanoparticles is about 9 when pH of PEI solution is 11. At pH 7.4, the magnetic nanoparticles with different charge adsorbed selectively proteins via electrostatic interaction.

Key words: magnetic particles, layer-by-layer self-assembly, zeta-potential, protein