Congo Red

Congo Red is used to stain microscopic preparates, especially as a cytoplasm and erythrocyte stain. Apple-green birefringence of Congo red stained preparates under polarized light is indicative for the presence of amyloid fibrils. Additionally, congo red is used in microbiological epidemiology to rapidly identify the presence of virulent serotype 2a Shigella flexneri, where the dye binds the bacterium's unique lipopolysaccharide (LPS) structure.

Use: For the detection of amyloid on formalin-fixed, paraffin-embedded tissue sections or may be used for frozen sections as well.

The amyloid deposits will be stained red and the nuclei will be stained blue.