Widely used in microbiology and molecular biology as a chromogenic substrate for detecting β-L-fucosidase enzyme activity. When the enzyme cleaves the glycosidic bond, it releases an indoxyl derivative that undergoes oxidation to form a blue or purple insoluble precipitate. This color change allows for easy visualization and identification of enzyme-producing organisms or transfected cells expressing the target gene. Commonly applied in bacterial colony screening, especially in recombinant DNA technology where it serves as a reporter system. Also used in histochemical staining to locate enzyme distribution in tissues. Its high specificity makes it valuable for selective detection in complex biological samples.