Suitable for ELISA. TMB One Solution is a chromagen substrate, 3,3´,5,5´-tetramethylbenzidine (TMB) provided in a mildly acidic, nonhazardous buffer for horseradish peroxidase detection in an ELISA format. The substrate is provided as a single solution at a ready-to-use working dilution. The substrate develops a blue reaction product when oxidized by peroxidase and a yellow reaction product in an endpoint multiwell assay after the addition of an acid solution.