Salt induced reduction of lysozyme adsorption at charged interfaces

A study of lysozyme adsorption below a behenic acid membrane and at the solid–liquid interface between aqueous lysozyme solution and a silicon wafer in the presence of sodium chloride is presented. The salt concentration was varied between 1 mmol L⁻¹ and 1000 mmol L⁻¹. X-ray reflectivity data show a clear dependence of the protein adsorption on the salt concentration. Increasing salt concentrations result in a decreased protein adsorption at the interface until a complete suppression at high concentrations is reached. This effect can be attributed to a reduced attractive electrostatic interaction between the positively charged proteins and negatively charged surfaces by charge screening. The measurements at the solid–liquid interfaces show a transition from unoriented order of lysozyme in the adsorbed film to an oriented order with the short protein axis perpendicular to the solid–liquid interface with rising salt concentration. (paper)