Cell viability measurement in animal cell culture relies on specific assays to distinguish live from dead cells, and the Coulter counter stands out as the method not used for this purpose. This question tests core knowledge in biotechnology and molecular biology labs. Understanding each option clarifies why option (D) is correct.

Trypan Blue Dye Exclusion

Trypan blue dye exclusion assesses cell viability by exploiting membrane integrity. Live cells with intact membranes exclude the dye, appearing clear under a microscope, while dead cells with compromised membranes take up the dye and stain blue. This quick, visual method is standard for routine checks during subculturing, often paired with a hemocytometer for counting.​

Tetrazolium (MTT) Assay

The MTT assay measures metabolic activity as a proxy for viability. Live cells reduce yellow MTT tetrazolium salt to purple formazan crystals via mitochondrial dehydrogenases, quantifiable by absorbance at 570 nm. It excels in high-throughput screening for cytotoxicity but can overestimate viability in metabolically altered cells.​

LDH Activity in Culture Medium

LDH activity detects cell death through enzyme release. Lactate dehydrogenase leaks from cells with damaged membranes into the medium, where its activity converts lactate to pyruvate, producing a colorimetric or fluorescent signal. This non-destructive supernatant assay is sensitive for apoptosis and necrosis detection.​

Coulter Counter Explanation

The Coulter counter, or cell counter, determines total cell concentration and size via electrical impedance changes as cells pass through an aperture. It counts all cells—live and dead—without distinguishing viability based on membrane integrity or metabolism. Used for total cell density, not viability, making it the incorrect choice here.​

Correct Answer and Key Takeaway

Option (D) Coulter counter is NOT used for cell viability measurement in animal cell culture. For biotech researchers optimizing cultures, prioritize dye exclusion or metabolic assays over particle counters to ensure accurate live/dead ratios.​