Figure and show SEIRA spectra of the incubation of Aβ with the two systems in the C=O stretch/amide region of 1850 -1500 cm -1 in H2O buffer, taking the corresponding membrane system before Aβ-addition as reference. In both cases, we observe a small feature at ~1740 cm -1 , a dominant broad band at ~1650 cm -1 , and a smaller one at ~1560 cm -1 all growing with time. These bands can be assigned to lipid C=O stretches, a convolution of the backbone amide I mode of Aβ and the H2O bending mode, and the backbone amide II mode of Aβ, respectively. The detection of the amide I during the adsorption process of a peptide/protein to a membrane overlapping with a positive H2O absorption intensity at ~1650 cm -1 is an unusual observation in SEIRA spectroscopy. As SEIRA relies on a plasmonic enhancement, the detected signals decay steeply with a d -6 -dependence (d = distance from Au surface), such that spectra are detected only of molecules located within roughly 10 nm from the Au surface. As a consequence, SEIRA spectra of the immobilization of peptides/proteins typically show (small) negative H2O contributions in SEIRA spectra, because H2O molecules are replaced by the adsorbing protein/peptide. Exceptions to this are, when structures are formed which relocate water molecule into the membrane. Therefore, we attribute the pronounced water signals in our spectra to changes in the water structure at the membrane interface or within the lipid head group regions as a consequence of Aβ addition and discuss the relevance of this observation in the final section.