Amyloid plaques in TASTPM mouse brain: Amyloid beta Ab 6E10 after Citric acid
Note the strong intracellular positivity. This is not seen after Formic acid AR (Link). Also,note slight difference in the plaque pattern of positivity between the two AR methods.
Compare these with the positivity obtained using Highman's Congo red. Note that, under brightfield conditions (Link) particularly, the Congo red appears far less sensitive.