8-Hydroxyquinoline-β-D-galactopyranoside is primarily used in biochemical and molecular biology research as a substrate for detecting β-galactosidase enzyme activity. This compound is particularly valuable in assays where the enzyme cleaves the galactopyranoside moiety, releasing 8-hydroxyquinoline, which can be easily detected due to its fluorescent properties. It is commonly employed in cell-based studies, such as monitoring gene expression in reporter gene assays, where β-galactosidase is used as a marker. Additionally, it is utilized in microbiology to identify bacterial species that produce β-galactosidase, aiding in diagnostic and research applications. Its sensitivity and specificity make it a useful tool for studying enzyme kinetics and cellular processes.