3,3′,5,5′-Tetramethylbenzidine (Cat No.:R069206) is an organic compound widely used as a chromogenic substrate in enzyme-linked immunosorbent assays (ELISAs) and other peroxidase-based detection systems. Structurally, TMB consists of two benzidine units each substituted with two methyl groups at the 3 and 5 positions, enhancing stability and reactivity. In the presence of hydrogen peroxide and peroxidase enzymes, TMB undergoes oxidative color changes—turning blue and then yellow upon acid stop—enabling sensitive visual and spectrophotometric detection. It is valued for its high sensitivity, low toxicity compared to older substrates, and reliability in biochemical assays.