4′,5′-dimethoxy-6-carboxyfluorescein: A novel dipole-dipole coupled fluorescence energy transfer acceptor useful for fluorescence immunoassays

A new nonfluorescent dye, 4′,5′-dimethoxy-6-carboxyfluorescein has been prepared which is a useful energy acceptor for energy transfer measurements from fluorescein in the study of distances within macromolecular assemblies. The R 0 value of 62 Å for the new dye-fluorescein pair is exceptionally high. The utility of this dye pair has been demonstrated in a fluorescence excitation transfer immunoassay for morphine.