5-Bromo-4-chloro-3-indolyl phosphate

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Skeletal formula of BCIP
Ball-and-stick model of the BCIP molecule
IUPAC name
(5-bromo-4-chloro-1H-indol-3-yl) dihydrogen phosphate
Other names
3D model (JSmol)
Molar mass 326.47 g·mol−1
Appearance Colorless
soluble in water (sodium salt)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

5-Bromo-4-chloro-3-indolyl phosphate (BCIP, X-phosphate, XP) is an artificial chromogenic substrate used for the sensitive colorimetric detection of alkaline phosphatase activity. It is, for example, used in immunoblotting, in situ hybridization, and immunohistochemistry, often in combination with nitro blue tetrazolium chloride (NBT).[1][2] 5-bromo-4-chloro-3-indoxyl is oxidized by atmospheric oxygen to form the blue dye 5,5′-dibromo-4,4′-dichloro-indigo. It is also oxidized by nitroblue tetrazolium (NBT), which forms an insoluble dark blue diformazan precipitate after reduction. Alkaline phosphatase is commonly conjugated to secondary antibodies.


  1. ^ http://www.sigmaaldrich.com/catalog/search/ProductDetail/SIGMA/B1026
  2. ^ Alkaline phosphatase hydrolyses BCIP to 5-bromo-4-chloro-3-indoxyl<JP Horwitz J. Med. Chem., 1966, 9 (3), pp 447–447 and inorganic phosphate