Used as a chromogenic substrate in biochemical assays to detect β-glucuronidase enzyme activity. When cleaved by β-glucuronidase, it releases indoxyl, which oxidizes in air to form a blue-insoluble pigment. This color change allows for visual or spectrophotometric detection, making it valuable in histochemistry, microbiology, and genetic screening. Commonly applied in bacterial identification, especially in detecting E. coli in water and food samples. Also utilized in molecular biology for reporter gene assays and in situ localization of gene expression in tissues. Its high sensitivity and low background make it suitable for both qualitative and quantitative analysis.