(502d) Modulating Protein-Surface Interactions Using Mixed Self-Assembled Monolayers

The ability of self-assembled monolayers (SAMs) to expose a wide range of functional groups on their surface allows protein-surface interactions to be probed in a controlled manner. With SAMs, protein adsorption studies have often been performed on flat surfaces under static conditions using methods such as ellipsometry, XPS, radio-labeling, and dye quantification. In these approaches, a surface that has been exposed to a protein solution typically undergoes a set of washing procedures before the amount of surface adsorbed protein is analyzed. As a result of procedural differences, there can be lab-to-lab variations in terms of the transition from a non-adsorbing to an adsorbing surface across surfaces of different compositions. More broadly, the role that shear rate has on protein adsorption remains uncertain. For example, the amount of adsorption onto a surface has been reported by different groups to increase, be unaffected, or to decrease with increases in shear rate. Here, we have investigated protein-surface interactions to mixed SAMs formed from Cl3Si(CH2)11(EG)3OCH3 (EG3OMe) and Cl3Si(CH2)7CH3 (C8). These SAMs are covalently anchored to their support and provide a means for creating surfaces of different surface energies. We determined the thicknesses, wettabilities, and surface compositions of the mixes SAMs using various methods of surface characterization. We examined protein-surface interactions onto these mixed SAMs under both static and shear-flow condition. The in-situ measurements of protein adsorption were performed in a flow cell that is integrated with a Total Internal Reflectance Fluorescence (TIRF) system. Using proteins differing in molecular weights and hydrophobicities, we were able to examine the interplay between shear rate, protein characteristics, and surface hydrophobicity and composition on protein adsorption and desorption. The results from this study address observed differences in the threshold conditions for establishing non-fouling behavior toward specific proteins and provide suggestions for broadly defining conditions where levels of protein adsorption may be modulated under flow and static conditions or made to be enhanced for specific proteins over others.