Widely used in molecular biology as a chromogenic substrate for detecting β-galactosidase enzyme activity. When cleaved by β-galactosidase, it releases an unstable indoxyl derivative that undergoes oxidation to form a blue insoluble precipitate. This reaction is commonly employed in blue-white screening of recombinant clones in bacterial colonies, allowing visual identification of successful gene insertions. Its high sensitivity and clear color development make it ideal for use in agar plates and histochemical staining. Also utilized in some diagnostic assays to detect enzyme expression in cells or tissues.