(1,1'-Biphenyl)-3,3',4,4'-tetramine (3,3'-Diaminobenzidine, DAB) is an organic benzidine derivative, that used as a precursor to polybenzimidazoles. As its water-soluble tetrahydrochloride, (1,1'-Biphenyl)-3,3',4,4'-tetramine has been used in immunohistochemical staining of nucleic acids and proteins. Diaminobenzidine is oxidized by hydrogen peroxide in the presence of hemoglobin to give a dark-brown color. This color change is used to detect fingerprints in blood. The solubility of (1,1'-Biphenyl)-3,3',4,4'-tetramin in water allows for adaptability compared to other detection solutions which use toxic solvents. In research, this reaction is used to stain cells that were prepared with hydrogen peroxidase enzyme, following common immunocytochemistry protocols. Relevant to Alzheimer's disease, Aβ protein amyloid plaques are targeted by a primary antibody, and subsequently by a secondary antibody, which is conjugated to a peroxidase enzyme. This will bind (1,1'-Biphenyl)-3,3',4,4'-tetramine as a substrate and oxidize it, producing an easily observable brown color. Plaques can then be quantified for further evaluation.