Ponceau S solution (CAS 6226-79-5 (solid))

Ponceau S solution is a synthetic azo dye commonly used in biological research for staining purposes. This dye is particularly noted for its application in the rapid and reversible staining of protein bands on nitrocellulose or polyvinylidene difluoride (PVDF) membranes, a process integral to Western blotting—a technique used to detect specific proteins in a sample. The mechanism by which Ponceau S operates involves the electrostatic interactions between the anionic dye molecules and the cationic amino acid residues of the proteins. When applied to a membrane, Ponceau S binds to the basic and hydrophobic regions of proteins, thereby rendering the protein bands visible. This is especially useful because it allows researchers to assess the efficiency of protein transfer from the gel to the membrane before proceeding with more specific immuno-detection methods. Furthermore, since the staining is reversible, the membrane can be destained with a mild solution, such as acetic acid or water, without damaging the proteins, which then allows for subsequent probing with antibodies.