Direct Red 80

Direct Red 80 (Sirius Red) is a polyazo dye used principally in staining methods for collagen and amyloid. Direct Red 80 does not release benzidine upon degradation and is safer than many traditional direct dyes^[1]. In Vitro: Direct Red 80 (Sirius Red) has two important uses in histopathology: staining collagen from solution in saturated aqueous picric acid and staining amyloid from an alkaline solution. Stained structures are red^[1].
Confocal laser microscopy (CLM) is also used to evaluate collagen production and distribution after Direct Red 80 staining. Direct Red 80 is not specific for the different types of collagen. Samples are washed in dH₂O, pretreats for 40 min with a solution of 0.2% phosphomolybdic acid (PMA) and incubates for 30 min in a solution consisting of 0.1% Direct red 80 diluted in saturated aqueous picric acid. Finally each sample is washed in 0.01 M HCl for 2 min. PMA is used to make colourless cytoplasm and HCl is used to remove non-specific staining^[1].