DAB tetrahydrochloride dihydrate is widely employed as a staining agent in histochemical (HC) and immunohistochemical (IHC) applications, where it plays an important role in peroxisomal staining procedures and in the detection of mitochondrial cytochrome c oxidase activity.

DAB tetrahydrochloride dihydrate, as a dye, is converted into an insoluble polymer upon oxidation, forming a dark brown precipitate in the reaction area, thereby enabling the visualization of target molecules. In immunohistochemistry, DAB tetrahydrochloride dihydrate serves as a substrate for peroxidase conjugated to primary or secondary antibodies. In histochemical staining Methods, DAB tetrahydrochloride dihydrate can be used to stain the activity of peroxisomes and mitochondrial cytochrome c oxidase (COX) in organelles [1].
Cytochrome c oxidase (COX) histochemical staining protocol [1] (This protocol is for reference only and can be adjusted according to specific experimental requirements):
1. Incubate the sections with ~50 µL COX staining solution (0.1 M NaPO4, 4 mM DAB tetrahydrochloride dihydrate, 100 µM cytochrome c, 2 mg/mL catalase) at 37°C for 45 minutes.
2. Wash three times with PBS, 5 minutes each, followed by sequential treatment with 75% and 95% ethanol for 1 minute each, and finally dehydrate with 100% ethanol for 10 minutes.
3. After staining, the samples must be completely dried before sampling.

The above information is based on published literature. Experimental procedures should be appropriately modified to meet specific research demands.