(415h) Understanding How Membrane Materials Influence Protein Adsorption and Membrane Fouling at the Single-Molecule Level

Membrane fouling, due to protein adsorption and accumulation on membrane surfaces, leads to decreased efficiency and selectivity of filtration processes.  Certain membrane materials, especially hydrophilic materials, have shown reduced protein accumulation and decreased membrane fouling.  However, a molecular-level mechanistic understanding of protein layer formation and macroscopic fouling behavior is still lacking and has been heavily debated in the literature.  Using single molecule (SM) imaging techniques, based on total internal reflection fluorescence microscopy (TIRFM), we are able to directly observe adsorption, desorption, and interfacial diffusion for millions of individual molecules.  This SM technique uniquely allows us to identify heterogeneous surface behavior and distinct dynamic rates (e.g. adsorption vs. desorption rates rather than net adsorption).  We investigated the interfacial dynamics of bovine serum albumin (BSA) and a human monoclonal antibody (IgG) on several commonly used membrane materials on both bare and protein crowded surfaces using SM TIRFM.  In particular, we were interested in the role of protein-surface interactions vs. interfacial protein-protein interactions and the independent effects of adsorption and desorption rates.  In the case of BSA, surface chemistry had little effect on adsorption and desorption rates on different bare surfaces.  Once a BSA layer formed, further protein adsorption was reduced and desorption was insensitive to the underlying surface chemistry, suggesting that protein-protein interactions play a large role in BSA monolayer and multi-layer formation.  In contrast, IgG interfacial dynamics showed some dependence on surface chemistry (adsorption and desorption varied) and desorption rates in most cases were insensitive to protein concentration (e.g the same for bare and protein crowded surfaces).  This suggests that for IgG surface chemistry directly influences protein-surface influences and can regulate protein-protein interactions. Ultimately, membrane material effects on protein adsorption dynamics and membrane fouling appear to be highly protein dependent.