Used primarily in cell viability and proliferation assays, this compound is reduced by metabolically active cells to form an insoluble purple formazan product. The amount of formazan produced is directly proportional to the number of viable cells, allowing quantification via spectrophotometry after dissolving the crystals. Commonly applied in cytotoxicity testing, drug screening, and evaluation of therapeutic agents in research laboratories. Due to its inability to penetrate dead or damaged cells, it selectively stains living cells, making it a valuable tool in assessing cell health and metabolic activity.