The adsorption of Mefp-1 on an oxidized iron surface was followed in real time using QCM-D as illustrated in Fig. 2. The sensed mass determined with QCM-D includes the mass of the adsorbed protein and that of water that is hydrodynamically coupled to the layer. This mass will be referred to as the “sensed mass” in this article to distinguish it from the adsorbed mass of the protein. The exposure to the Mefp-1 solution leads to initial rapid adsorption, as expected for a protein showing high affinity for the adsorbent. After this initial rapid adsorption, a slower increase in the sensed mass is observed, suggesting a continuous build-up of the Mefp-1 layer. Since the substrate is a pre-conditioned iron surface that is not as stable as a model silica surface, the adsorption of Mefp-1 was interrupted after 10 min to prevent non-negligible corrosion of the substrate within the period of measurement. The protein solution was removed by injection of a protein free 10 μm FeCl3 solution into the cell, which allows the investigation of Fe3+ enhanced complexation of the pre-adsorbed protein layer. As shown in Fig. 2, the exposure of the adsorbed layer to the FeCl3 solution leads to a decrease in the sensed mass, which can arise from removal of some loosely bound Mefp-1 and/or some of the coupled water in the protein layer. Further information can be obtained from the change in the dissipation (ΔD) values.
adsorption of Mefp-1
interrupted
10 min
min
FeCl3
10 μm
μm