Daniel Carvajal Graduate Student BS MSE and Bioengineering 2003, University of California Berkeley Cook Hall 2009, 1-3675 dcarvy at northwestern dot edu

Model liquid/liquid interfaces

Receptor-ligand interactions control cellular response to a wide range of phenomena and provide communication between cells in multi-cellular organisms. The specific binding of ligands to receptors is used to activate, regulate and inhibit many processes such as muscle contraction, growth and glucose levels for example. Of interest to our group is that receptor-ligand interactions control how cells stick to each other and to other surfaces. The understanding of these processes is key in biotechnological device design where sometimes cell attachment is desired, such as bone scaffolds, and sometimes cell attachment is unwelcome, such as an artificial heart valve. 

In this research we have used the strong and specific binding of streptavidin to biotin (vitamin H) to model the ligand-receptor interaction. Polymeric amphiphiles end-capped with biotin were synthesized giving a molecule that can bind to streptavidin. In our model system, ligand-receptor binding only takes place at the oil-water interface between a chloroform drop and the embedding water phase allowing us to use drop shape analysis (DSA) to monitor the interaction. In DSA, the drop profile is recorded and analyzed providing the interfacial tension between the two fluids. Molecules adsorbed to this interface, such as our polymeric amphiphiles, lower the interfacial tension allowing their presence to be detected through the technique. The adsorption of more molecules to the oil-water interface, like the binding of streptavidin to the biotinylated amphiphiles further lowers the interfacial tension, allowing this interaction to also be detected using DSA.