CUG is widely used as a fluorescent substrate in enzymatic assays, particularly for detecting β-galactosidase activity. Its application is crucial in molecular biology and biochemistry research, where it helps in monitoring gene expression and studying enzyme kinetics. When β-galactosidase acts on CUG, it releases a highly fluorescent product, 3-carboxyumbelliferone, which can be easily measured using fluorescence spectroscopy. This property makes CUG a valuable tool in high-throughput screening assays, cell-based reporter systems, and diagnostic tests for identifying bacterial species that express β-galactosidase. Additionally, it is employed in histochemical staining to visualize enzyme activity in tissues or cells, aiding in the study of cellular processes and disease mechanisms.