ONPG Solution is widely used in microbiology and biochemistry as a substrate for detecting β-galactosidase enzyme activity. It is particularly useful in molecular biology experiments to identify and study bacterial colonies that express the lacZ gene, which encodes β-galactosidase. When ONPG is hydrolyzed by the enzyme, it produces a yellow compound, o-nitrophenol, allowing for easy visual or spectrophotometric detection of enzyme activity. This makes it a valuable tool in cloning experiments, gene expression studies, and screening for recombinant DNA technology. Additionally, it is employed in diagnostic assays to differentiate bacterial species based on their ability to metabolize lactose.