ATP, XTT, and WST-8 assays are widely used methods for assessing cell viability and proliferation in biological research. The ATP assay is a highly sensitive bioluminescence-based technique that directly measures cellular ATP levels, providing rapid results and the ability to detect even a single cell. The XTT assay, a colorimetric method, relies on the reduction of the tetrazolium salt XTT by metabolically active cells to produce a water-soluble orange formazan product. Similarly, the WST-8 assay is a newer tetrazolium-based method that offers improved sensitivity and water solubility compared to earlier tetrazolium assays. Both XTT and WST-8 assays are simpler to use as they don't require a cell lysis step, but may need longer incubation times compared to the ATP assay. These assays are valuable tools in various applications, including cytotoxicity studies, drug screening, and cell proliferation analysis, with the choice of assay depending on specific research requirements such as sensitivity, speed, and the cellular process being investigated.