DIFFUSION AND ADSORPTION OF PROTEINS IN A MODEL PORE IN THE SURFACE FORCES APPARATUS

When the energetic interactions between proteins and pore surfaces are favorable, both hindered diffusion and adsorption govern the overall transport rates in fine pores. To study these effects, we have used th e narrow gap between mica surfaces in a surface forces apparatus (SFA) as a model slit-like pore that has a well-characterized geometry and surface chemistry. The optical technique of multiple beam interferomet ry used in the SFA for measuring surface separations also provides a m eans for determining protein concentrations inside the pore. The resul ts obtained show the effect of ionic strength on the net transport rat es for lysozyme diffusing in a mica-bounded pore, a consequence of the influence of electrolyte screening on the extent of adsorption. It is also seen how adsorption on opposing surfaces leads to pore blockage once the pore size decreases to 2-3 times the molecular diameter. Alth ough quantitative determination of hindrance effects is potentially al so possible using the method, an improved method for acquisition of th e interferometry data must first be implemented.