Staining for amyloid is one of the most useful special techniques. The Congo red stain and examination with nonpolarized and polarized light are the most frequently used techniques. The dye binds the beta-pleated arrangement of amyloid and has no chemical specificity.
This is seen as a reddish deposit under nonpolarized light. Green birefringence is present when the sections are examined under polarized light. Excessive or prolonged exposure to Congo red can cause binding to the tissue that is unrelated to the presence of amyloid. [Read more...]