Used as a biological stain to detect enzyme activity, particularly in histochemistry and microbiology. It acts as an electron acceptor in dehydrogenase enzyme reactions, forming an insoluble blue formazan precipitate when reduced, making it useful for visualizing cellular metabolic activity. Commonly applied in viability assays to distinguish live cells from dead ones, as only metabolically active cells reduce the dye. Also employed in immunohistochemistry and blotting techniques as a chromogenic agent for detecting specific proteins or nucleic acids.