Used as a chromogenic substrate in enzymatic assays to study the activity of beta-galactosidase enzymes, which hydrolyze it to release p-nitrophenol, a yellow-colored product measurable by spectrophotometry. Helps in biochemical research to understand enzyme kinetics and mechanisms. Applied in diagnostic kits for detecting enzyme presence or activity in biological samples. Utilized in microbiology for identifying bacterial species that produce beta-galactosidase, such as in the ONPG test. Supports the development of therapeutic agents targeting enzyme-related disorders, including in genetic engineering studies for gene expression analysis.