Trypan blue is a dye commonly used in biological research to assess cell viability. It selectively stains dead cells, allowing scientists to distinguish between live and non-viable cells under a microscope. When added to a cell sample, live cells remain clear, while dead cells take on a blue color. This dye is particularly useful in various applications, including cell culture and toxicology studies. By determining the proportion of live versus dead cells, researchers can evaluate the effects of treatments or conditions on cell health and function.