Transmission electron microscopy of tau-polyP fibers

Samples from the thioflavin T aggregation assay were analyzed by transmission electron microscopy. A sample (∼5 μL) was applied onto a thin, amorphous carbon-layered 400-mesh copper grid (Pelco, Fresno, CA) and incubated for 3 min before removing the liquid with filter paper. The grid was washed twice with 5 μL ddH₂O followed by two applications of 5 μL 0.75% uranyl formate (pH 5.5–6.0). The liquid was aspirated, with care taken to not disturb the sample. Grids were imaged at room temperature using a Morgagni microscope (FEI, Hillsboro, Oregon) operating at 100 kV. Images were acquired on a CCD camera at 22,000× resulting in a sampling of 2.1 Å/pixel.