ponceau

Ponceau refers to a family of synthetic red dyes used in laboratory staining and, in some contexts, as a food colorant. The most widely used member is Ponceau S, a soluble azo dye employed to stain proteins on nitrocellulose or PVDF membranes during or after protein transfer steps, such as Western blotting. The stain provides a quick, non-specific visualization of total protein to verify transfer efficiency and sample loading. Ponceau S staining is reversible: it can be removed with water or dilute acidic solutions to allow subsequent immunodetection or further staining.

In practice, Ponceau S binds to proteins mainly through noncovalent interactions, making it a convenient, temporary stain. Its use is typically followed by destaining to restore a clear background for procedures like antibody probing. Because it is not protein-specific, researchers often view it as a preliminary check rather than a final analysis.

Beyond Ponceau S, the term ponceau also appears in reference to related dyes and formulations used for histological staining, as well as to other red food-grade dyes that share the general “ponceau” color family. A notable example outside histology is Ponceau 4R, a synthetic red dye used as a food coloring (often referred to by regulatory codes such as E124 in some regions). Its use is subject to regulatory oversight due to health and safety considerations in different jurisdictions.

The name ponceau derives from the designation of a bright red color in the traditional dye family, with historical development dating to the 19th century.