||DCFH (commonly known as dichlorofluorescin) is used as an indicator of peroxynitrite formation.DCFH is supplied as the diacetate ester. Following enzymatic or base-catalyzed cleavage of the diacetate groups, it is readily oxidized to the highly fluorescent product dichlorofluorescein (DHF). Peroxynitrite is an efficient mediator of this oxidation and neither NO, superoxide, nor hydrogen peroxide alone appear to oxidize DCFH. Formation of DHF can be monitored by fluorescence spectroscopy using excitation and emission wavelengths of 502 and 523 nm, respectively, or by absorbance spectroscopy at 500 nm (? = 59,500 M?1cm?1).