(131b) Protein–Membrane Molecular Interactions and Membrane Filtration

Two microfiltration membranes were selected and chemically modified to exhibit low affinity toward proteins, respectively. These two modified membranes (0.2 µm mPVDF and mPES), were characterized by SEM, ATR-FTIR, Z-potential and contact angle. Streptavidin (SA) was selected because of its stability in a wide range of pH and ionic strength (I) and immobilized onto nano- and micro-particles for filtration experiments and atomic force microscopy measurements, respectively. To gain insight into the interaction forces between protein-coated particles and membranes, the solution conditions (pH = 4.0, 5.0, 6.0, 7.4 and 9.0 and I = 1, 5, 10, 50, 100 mM buffers), and nanoparticle support material (silica) were varied. AFM was used in force-volume mapping mode: 400 measurements, scanning 20 x 20 µm² surface area for each of the 20 conditions. Based on adhesion forces and protein pulling events, we showed that for mPVDF and mPES, the adhesion forces at and above pH 6 were relatively independent of I. These data correlated with results from filtration experiments. This work demonstrates that AFM can be used to screen proteins and operating conditions in order to reduce fouling or to increase protein capture.