Christine Galitsky

Thesis Abstract:

Dynamics of Protein Adsorption at Fluid/Fluid Interfaces as Studied by the Sessile Drop Technique

by Christina Galitsky

Master of Science in Chemical Engineering University of California, Berkeley
Professor Harvey W. Blanch, Co-chair
Professor Clayton J. Radke, Co-chair

Protein adsorption at fluid/fluid interfaces influences many applications in the pharmaceutical, food, and medical industries. Protein adsorption at air/water and oil/water interfaces has been observed previously. In order to study reversibility and obtain a more detailed picture of the adsorption process, we have developed a flow cell incorporated into an inverted sessile drop apparatus. This apparatus enables flow of protein-free solutions through the cell containing the adsorbing protein. By allowing flow through the cell, we can measure the interfacial tension of the inverted sessile drop (or bubble) during adsorption, during washout, after washout, and during reloading of the protein. Studies employing a reversibly adsorbing surfactant confirmed our ability to measure adsorption and desorption with the new cell.

Adsorption and desorption of hen egg-white lysozyme and chicken egg albumin (ovalbumin) were studied at both the air/water and oil/water interfaces using the new inverted sessile drop apparatus. Dynamic interfacial tensions indicate that both proteins adsorb at both interfaces. The characteristics of adsorption before and after washout depended on the concentration of the bulk protein solution. The characteristics of the adsorption curve after washout was also related to the length of adsorption time. Washout of the bulk aqueous phase at both the air/water and the oil/water interfaces did not increase the interfacial tension for either protein. The protein at the interface is not removed by washout of the protein solution in the bulk phase.

We proposed a molecular model for lysozyme and ovalbumin that is supported by our data. For lysozyme, we propose that adsorption to the interface included unfolding into the interface and lateral unfolding and linking between molecules of lysozyme. Thus, we see a tight get network at the interface over long periods of time. For ovalbumin, we propose that the molecules adsorbed to the interface and unfolded into the interface, but, due to its size, formed a more open network of interconnecting ovalbumin molecules