WST1

WST-1 is a water-soluble tetrazolium salt used in colorimetric assays to estimate cell viability and proliferation. In metabolically active cells, WST-1 is reduced by cellular dehydrogenases to a water-soluble formazan dye, the amount of which correlates with the number of viable cells. The reaction typically requires an electron mediator such as phenazine methosulfate (PMS) and is measured by absorbance with a spectrophotometer, usually near 450 nm.

Assays are performed by adding WST-1 to cultured cells, incubating for a period (often 1–4 hours), and measuring the absorbance of the culture medium. Because the formazan produced is water-soluble, no dissolution step is required, simplifying handling and making the assay well-suited for microplate formats and high-throughput screening.

Advantages of WST-1 include its water solubility, which eliminates solubilization steps required by some other tetrazolium assays, and its broad compatibility with routine cell culture work. The assay is generally less toxic than MTT, allowing shorter or repeated measurements in some setups.

Limitations include dependence of the signal on cellular metabolic state rather than strictly on cell number, which can be influenced by culture conditions or treatment. Interference can arise from reducing agents, serum components, phenol red, or compounds that alter redox balance. The response may also be non-linear at high cell densities, so calibration with a standard curve is recommended.

Applications include viability and cytotoxicity testing, proliferation studies, and drug screening. It is commonly used in laboratories alongside related tetrazolium assays such as MTT, MTS, XTT, and WST-8.