Acid Black 2

Live/dead viability and cytotoxicity staining assays are based on the simultaneous detection of intracellular esterase activity in metabolically active (viable) cells and membrane integrity loss in non-viable cells. In commonly used dual-staining approaches, membrane-permeant fluorogenic substrates are converted by intracellular esterases into fluorescent products in live cells, while impermeant DNA-binding dyes selectively enter cells with compromised plasma membranes and label nucleic acids in dead or dying cells, enabling discrimination between viable and non-viable populations by fluorescence microscopy or flow cytometry.

Sperm thawing for functional recovery is a post-cryopreservation procedure designed to restore and measure sperm motility, viability, membrane/acrosome integrity, DNA integrity, and usable motile sperm yield after freezing-induced injury; published human studies show that cryopreservation reduces motility and viability and can damage the plasmalemma, acrosome, tail, and DNA integrity. The experimental readout is generated by comparing post-thaw motility recovery, viability, acrosomal status, DNA integrity, and recovered motile sperm after thawing and optional sperm-selection steps; thawing at 40°C improved motility recovery compared with 20-37°C without significant differences in viability, ATP content, acrosomal status, or DNA integrity in one human donor-semen study.

The following protocol uses the MTT colorimetric assay as a classic literature-established method for assessing cell viability/metabolic activity in cultured mammalian cells. MTT[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] is reduced by metabolically active cells to a colored formazan product; the amount of formazan is quantified spectrophotometrically and provides an indirect measure of metabolically active viable cells. Importantly, MTT reduction reflects cellular oxidoreductase/metabolic activity rather than an absolute direct count of living cells, so changes in cellular metabolism can alter the signal independently of cell number.