What are the common chromogens used in?

3,3'-Diaminobenzidine (DAB) is widely used in immunohistochemistry (IHC) and in situ hybridization (ISH) for visualizing the presence of target molecules in tissues or cells. DAB forms a brown precipitate upon oxidation by enzymes like horseradish peroxidase (HRP). 3,3',5,5'-Tetramethylbenzidine (TMB) is a chromogen commonly used in enzyme-linked immunosorbent assays (ELISA) and other immunoassays. TMB produces a blue color upon reaction with HRP, which can be quantified spectrophotometrically. Fast Red is used in immunohistochemistry for visualizing enzyme activity. Fast Red produces a red color upon reaction with alkaline phosphatase. Nitroblue tetrazolium chloride/5-Bromo-4-chloro-3-indolyl phosphate (NBT/BCIP) is used for developing blots or for in situ hybridization. It produces a blue/purple precipitate upon reaction with alkaline phosphatase.