Phenazine methosulfate (PMS) is widely used as an electron transfer mediator in biochemical and analytical applications. It plays a key role in enzyme-coupled assays, particularly in colorimetric and fluorometric detection systems where it enhances signal sensitivity. PMS is commonly employed in dehydrogenase-based tests, such as those for glucose, lactate, and cholesterol, by shuttling electrons from the enzyme to a secondary dye that produces a measurable color change. It is also utilized in microbial fuel cells and redox cycling systems to improve electron transport between microorganisms and electrodes, increasing power output and detection efficiency. In cell-based assays, PMS serves as a cofactor in viability tests like the MTT assay, helping convert tetrazolium salts into formazan by accepting electrons from cellular reductases. Due to its ability to penetrate cell membranes, PMS is effective in intracellular redox reactions, making it valuable in studies of oxidative stress and mitochondrial function. Its strong redox potential and solubility in aqueous solutions make it a preferred mediator in biosensors and diagnostic kits.