TMB ELISA Peroxidase Substrate (3, 3', 5, 5' - Tetramethylbenzidine) is a chromogenic substrate used to visualize antibody reactivity in ELISA experiments. In the presence of peroxidases, TMB can act as an electron donor for the conversion of peroxides to water, changing the color of solution to a blue color equivalent to the degree of reactivity. This reaction can be halted with acid to change the TMB to yellow.Synonyms: 3,3',5,5'-Tetramethylbenzidine; TMB-E; TMBE