Used as a vital staining agent in cell viability and metabolic activity assays, serving as a substrate for mitochondrial dehydrogenases in living cells. Upon reduction by metabolically active cells, it forms a red-fluorescent formazan product that can be quantified fluorometrically, enabling assessment of cell proliferation, cytotoxicity, or metabolic activity. Its lipophilic nature facilitates efficient cellular uptake. Commonly applied in cancer research, drug screening, and toxicity testing to evaluate the effects of compounds on cell health.