Used as a chromogenic substrate in microbiological assays for the detection of β-D-fucosidase enzyme activity. When cleaved by the enzyme, it releases an indoxyl derivative that undergoes oxidative dimerization to form a blue-colored, insoluble precipitate. This reaction is employed in selective media and histochemical staining to identify specific bacterial strains expressing β-D-fucosidase, particularly in clinical and environmental microbiology. Its specificity allows for differentiation of microorganisms in culture, aiding in diagnostic workflows.