Protein phosphatase, an enzyme that controls the removal of phosphate (PO43-) group from protein molecules, regulates many fundamental cellular processes such as cell attachment, proliferation, differentiation and apoptosis. Elevated level of alkaline phosphatase expression is one of the most widely used stem cell marker. ScienCell™ Alkaline Phosphatase Assay is optimized to detect phosphatase activity in biological samples using pNPP (4-nitrophenyl phosphate) as a colorimetric substrate. A water-soluble yellow product with a strong absorption at 405 nm is developed during the reaction of pNPP with phosphatase and can be detected with an ELISA plate reader.