Single molecule observations of multiple protein populations at the oil-water interface

Single-molecule total internal reflectance fluorescence microscopy was used to observe the dynamic behavior of >4000 bovine serum albumin objects at the silicone oil-water interface. The surface residence time distribution indicated the presence of three populations at the interface. Each population had a characteristic fluorescence intensity and distinctive interfacial diffusion behavior. Larger fluorescence intensity correlated with longer residence times and slower diffusion. These combined observations of fluorescence intensity, surface residence time, and interfacial diffusion suggested that the three populations represent monomers, dimers, and trimers respectively.