TMB (3, 3', 5, 5' - Tetramethylbenzidine) is a chromogenic substrate used to visualize antibody reactivity in ELISA experiments. TMB Substrate Solution (For ELISA) can be used in micro well ELISA for HRP detection. In the presence of peroxidases, TMB acts as an electron donor for the conversion of peroxides to water, developing soluble blue reaction product that may be read at 370 or 655 nm. This reaction can be stopped with acid, forming a yellow reaction product that may be read at 450nm.