Transmission EM
β2m fibrils were used without dilution and negatively stained with 2% (wt/vol) uranyl acetate on thin carbon films supported on holey carbon coated EM grids. Microscopy was carried out on a Tecnai 10 (FEI, Eindhoven, NL) operating at 100 kV with a low electron dose and defocus values of 700–900 nm. For cryo-EM, the fibrils were vitrified on holey carbon support films. Cryo-EM was performed using a Tecnai F20 with a field emission gun operating at 200 kV. Low electron dose images were recorded on Kodak SO163 film at 29,000×, with defocus in the range 1–2.6 μm.