Aβ 25-35 (Figure , S1a) and Amylin 20-29 (Figure , S1d) fibrils were prepared as described by Harper et al. Briefly, Aβ 25-35 was prepared by dissolving 2 mg of peptide in 1 mL of Milli-Q water. PBS (2x, PH 7.4) was slowly added to the sample to volume up to 2 mL, and the sample was inverted three times to mix the solution. The final concentration was 0.94 mM peptide and 0.01 % (v/v) NaN 3 . Aggregates could be visually seen after sample preparation. The sample was incubated for 4 days at 37 • C prior to experiments. The amylin 20-29 sample was prepared by a modified procedure from Madine et al. Briefly, 2.5 mg of amylin 20-29 was disaggregated using 20 µL DMSO for 1 h. PB (pH 7.12) was added to the sample to volume up the solution to 2 mL. The final concentration was 1.25 mM peptide and 0.01 % (v/v) NaN 3 . The sample was incubated at 22 • C. Aggregates could be visually observed within 24 h of incubation.