Abstract:  The effect of ligand density on the adsorption behavior of proteins was investigated using dual polarization interferometry (DPI)．The sensor chips of DPI were modified with 3-aminopropy-l-triethoxysilane (DAPTMS). The ligand densities on the modified chips were compared using X-ray photoelectron spectroscopy．Lysozyme， myoglobin， chymotrypsin， bovine serum albumin and immunoglobulin were used as model proteins. The adsorption behaviors of five proteins, such as adsorption amount, adsorption density and spatial structure, on the modified chips were characterized using DPI. It was found that with the increase of ligand density, the adsorption amount and density of proteins at the interface increase. Meanwhile, the initial adsorption rate grows. The spatial structure of proteins, especially immunoglobulin, was closely related with ligand density. The thickness of adsorption immunoglobulin layer was much smaller than the molecular diameter. The results indicated that the ligand density on the modified chip affected the amount, density and spatial structure of proteins on the interfaces．

Key words: ion exchange chromatography, ligand density, adsorption behavior, dual polarization polarization interferometer