For the colorimetric detection of alkaline phosphatase-labeled molecules, 5-Bromo-4-chloro-3-indolyl phosphate (BCIP) and Nitro Blue Tetrazolium (NBT) are available. The BCIP/NBT substrate system is versatile and functions in a variety of applications, including Northern Southern, and Western blotting, in situ hybridization, and immunohistochemistry.
BCIP is provided in two salt forms: the disodium salt which is soluble in water and the p-toluidine form which is soluble in dimethylformamide. These salt forms may be used to prepare a stock solution that in combination with NBT and a reaction buffer, form a substrate solution for alkaline phosphatase. This substrate system, when incubated with alkaline phosphatase, produces an insoluble NBT diformazan product that is easily observable with its purple color. For added convenience, a mixture of BCIP and NBT is provided in an easily dissolvable tablet form or as a ready-to-use liquid.