Evans blue
Evans blue free acid is a naphthalenesulfonic acid that is the free acid form of the dye Evans blue. The tetrasodium salt is used as a counterstain, especially in fluorescent methods to suppress background autofluorescence. It has a role as a sodium channel blocker and a teratogenic agent. It is a bis(azo) compound, a naphthalenesulfonic acid, a member of azobenzenes, a member of naphthols, a member of biphenyls, an aminonaphthalene and a primary arylamine. It is a conjugate acid of an Evans blue(4-).