Adsorption Behavior of Lysozyme and Tween 80 at Hydrophilic and Hydrophobic Silica–Water Interfaces

Nonionic surfactants such as Tween 80 are used commercially to minimize protein loss through adsorption and aggregation and preserve native structure and activity. However, the specific mechanisms underlying Tween action in this context are not well understood. Here, we describe the interaction of the well-characterized, globular protein lysozyme with Tween 80 at solid–water interfaces. Hydrophilic and silanized, hydrophobic silica surfaces were used as substrates for protein and surfactant adsorption, which was monitored in situ, with ellipsometry. The method of lysozyme and Tween introduction to the surfaces was varied in order to identify the separate roles of protein, surfactant, and the protein–surfactant complex in the observed interfacial behavior. At the hydrophobic surface, the presence of Tween in the protein solution resulted in a reduction in amount of protein adsorbed, while lysozyme adsorption at the hydrophilic surface was entirely unaffected by the presence of Tween. In addition, while a Tween pre-coat prevented lysozyme adsorption on the hydrophobic surface, such a pre-coat was completely ineffective in reducing adsorption on the hydrophilic surface. These observations were attributed to surface-dependent differences in Tween binding strength and emphasize the importance of the direct interaction between surfactant and solid surface relative to surfactant–protein association in solution in the modulation of protein adsorption by Tween 80.