4-Aminophenyl phosphate monosodium salt hydrate is widely used in biochemical research as a substrate for alkaline phosphatase enzymes. It plays a crucial role in enzyme activity assays, where its hydrolysis by the enzyme produces a detectable product, often used in colorimetric or fluorometric detection methods. This compound is also employed in the development of biosensors and diagnostic kits, particularly for detecting alkaline phosphatase levels, which are important biomarkers in various clinical conditions. Additionally, it finds application in immunohistochemistry and molecular biology techniques for visualizing and quantifying enzymatic activity in tissue samples or cellular assays. Its stability and reactivity make it a valuable tool in both research and diagnostic laboratories.