Extracting the time-dependent evolution of the 2 nd derivative signals at amide I positions of 1694 and 1634 cm -1 , and for amide II at 1560 cm-1 (Figure and) reveals additional interesting differences between the membrane systems. For tMLMs, we note a Langmuir-type adsorption behavior for all three peak positions, suggesting a direct adsorption of Aβ to the membrane interface. Instead, for tBLMs, we see a steady evolution for the 1634 cm -1 and 1560 cm -1 bands, and a more complicated behavior of the 1692 cm -1 , which reaches a minimum (i.e., maximum in absorbance . spectra) at approx. 4 h and then regresses back towards the zero line. This points to an initial fraction of antiparallel β-sheets, which transforms to parallel β-sheets with time. In addition, we note a drastically different amide I-to-amide II ratio (1634 cm -1 to 1560 cm -1 ) of roughly 2 for tMLMs, but ~4 for tBLMs. The amide I-to-amide II ratio is a sensitive marker for the orientation of secondary structure elements due to the different orientations of the transition dipole moments underlying the amide I and amide II modes. This suggests that we detect a change of the orientational alignment Aβ oligomers with respect to the membrane plane in our SEIRA experiments.