Ponceau S is widely used as a biological stain, particularly in protein detection. It is commonly applied in gel electrophoresis to visualize proteins separated on polyacrylamide gels. The stain binds to proteins, producing a reddish-pink color, which allows researchers to quickly assess protein bands and their migration patterns. This makes it a valuable tool in molecular biology and biochemistry labs for analyzing protein samples. Additionally, Ponceau S is used in Western blotting as a reversible stain to confirm protein transfer from gels to membranes before proceeding with antibody-based detection. Its ease of use and quick results make it a popular choice for preliminary protein analysis.