Widely used in molecular biology and microbiology as a chromogenic substrate for detecting enzyme activity. Specifically cleaved by β-N-acetyl-galactosaminidase enzymes, producing a blue-colored insoluble precipitate upon hydrolysis. This reaction is commonly employed in histochemistry, enzyme assays, and in situ hybridization to visualize gene expression or enzyme distribution in tissues and cells. Also utilized in agar-based bacterial identification systems, where the presence of specific enzymes in microorganisms leads to color development, aiding in rapid differentiation and screening. Its high specificity makes it valuable in diagnostic applications and recombinant protein detection, especially in cloning and screening of transformed colonies.