Used as a substrate in histochemical staining to detect esterase enzyme activity in tissue sections. It is particularly useful in identifying and localizing nonspecific esterases in cells, aiding in the differentiation of cell types in hematological and pathological studies. When hydrolyzed by esterase enzymes, it releases 1-naphthol, which couples with diazonium salts to form insoluble colored precipitates at the site of enzyme activity. This reaction helps visualize enzyme distribution under the microscope, making it valuable in diagnostic pathology and biological research.