128 as described

128 as described previously (Van Camp et al., 2010). These polymers were immobilised on gold from ethanol, water, or 50:50 solution of these solvents. The created surfaces were then submitted to human serum albumin (HSA) adsorption (concentration 200 µg/ml, pH adjusted with HCl and NaOH, I adjusted with NaCl). Polymer assembly was assessed by means of contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Polymer assembly and protein adsorption were monitored in situ by means of quartz crystal microbalance with dissipation monitoring (QCM-D). Results & Discussion Exploratory experiments have been performed on homogeneous PEO or PAA brushes in order to study the assembly process as well as HSA adsorption from solutions with different pH and I. The successful assembly of both polymers on gold could be observed by contact angle measurements, AFM and XPS. Brush thicknesses of about 1 nm for PEO and about 3 nm for PAA were measured by AFM. These results are compatible with the level of Au signal detected by XPS. QCM-D measurements performed in real time show the swelling or shrinking of PAA depending on pH and I. These observed effects are in agreement with those obtained previously by means of other techniques by other groups. QCM-D monitoring of HSA adsorption allowed conditions of PEO assembly to be identified for which HSA adsorption was nearly totally prevented. On PAA, adsorption could be prevented at high pH while it was enhanced when pH was lowered. These effects were modulated by I. Other groups have shown that when protein adsorption occurs on PAA, proteins are adsorbed deeply inside the brush and retain their secondary structure as well as their activity (Hollman et al., 2008; Haupt et al., 2005; Czeslik et al., 2004). Conclusions & Perspectives Assembly conditions leading to prevention of protein adsorption on PEO and PAA homobrushes were identified, as well as conditions which provide a mild environment for proteins on PAA. Promising results on mixed brushes are obtained. References _______________________________________________ Czeslik C., Jackler G., Hazlett T., Gratton E., Steitz R., Wittemann A. & Ballauff M. 2004. Salt-induced protein resistance of polyelectrolyte brushes studied using fluorescence

correlation spectroscopy and neutron reflectometry. Physical Chemistry Chemical Physics 6(24), 5557-5563. Haupt B., Neumann T., Wittemann A. & Ballauff M. 2005. Activity of Enzymes Immobilized in Colloidal Spherical Polyelectrolyte Brushes. Biomacromolecules 6(2), 948-955. Hollmann O., Steitz R. & Czeslik C. 2008. Structure and dynamics of alpha-lactalbumin adsorbed at a charged brush interface. Physical Chemistry Chemical Physics 10(10), 1448-1145. Van Camp W., Du Prez F.E., Alem H., Demoustier-Champagne S., Willet N., Grancharov G. & Duwez A.-S. 2010. Poly(acrylic acid) with disulfide bond for the elaboration of pHresponsive brush surfaces. European Polymer Journal 46( 2), 195-201. Acknowledgments _________________________________________ M.F. Delcroix is a Research Fellow of the Belgian National Foundation for Scientific Research (FNRS). W. Van Camp thanks the Fund for Scientific Research – Flanders (FWO) for a postdoctoral fellowship. 129