Used as a chromogenic substrate in enzymatic assays, particularly for detecting phosphatase enzyme activity. When dephosphorylated by alkaline phosphatase, it produces a colored naphthol derivative that can be measured spectrophotometrically. Commonly employed in biochemical research and diagnostic tests to monitor enzyme kinetics or as a detection reagent in immunoassays. Its disodium salt form enhances water solubility, making it suitable for use in aqueous reaction systems.