A more realistic model for protein adsorption which can adequately describe the non-reversibility, history dependence, or the Vroman-effect, was constructed. A novel instrument, the Single Channel Grating Coupler (SCGC) was used to provide new insight into proteins at interfaces. With the SCGC it is possible to probe the adsorption and exchange behavior of proteins on different surfaces. In situ measurements of interfacial exchange reactions provide sufficient data to develop a protein adsorption and exchange model. The large difference between the single curves indicates that proteins are exchanged and the adsorbed protein layer is not static.