Bromophenol blue is present as a sulfonated hydroxyquinone in acidic aqueous solutions. It is also known as tetrabromophenolsulfonphthalein.Bromophenol Blue is a pH indicator and a dye appearing as a strong blue color. It has a slight negative charge and will migrate the same direction as DNA, allowing the user to monitor the progress of molecules moving through the gel. The rate of migration varies with gel composition.
Bromphenol Blue is used as a tracking dye in DNA, RNA (agarose), and protein (polyacrylamide) gel electrophoresis. It has been used in the preparation of protein samples for western blotting analysis. Bromophenol blue migrates at approximately the same rate as 300-500bp DNA in agarose gel and at the buffer front in protein polyacrylamide gels. It has also been known for its use as a vital stain to probe the blood-brain barrier.