Adsorption and reorientation kinetics of lysozyme on hydrophobic surfaces

Using total internal reflectance fluorescence (TIRF), we observe that lysozyme adsorption onto hydrophobic surfaces can exhibit kinetic overshoots at some conditions, while, at lower free solution concentrations or flow rates over the surface, the coverage monotonically approaches its final value. This behavior is explained by an interfacial relaxation from an end-on to a side-on orientation, which occurs by rollover and not by the displacement of end-on adsorbed proteins by side-on adsorbing proteins. Rollover and displacement models are compared with data to prove this point. Ultimately, we quantitatively predict the kinetic traces for a variety of different adsorption histories (free solution concentration, flow rate, interruption of adsorption by flowing solvent) using a rollover model with reversible transport-limited adsorption of end-on oriented lysozyme and a single rollover rate constant.