Hydrophilic fluorescein derivatives: useful reagents for liposome immunolytic assays.

Hydrophilic derivatives of fluorescein containing hydroxyalkyl substituents were synthesized and encapsulated within liposomes. The fluorophores showed significantly more retention with time than did fluorescein, carboxyfluorescein, or calcein. Unlike calcein, the fluorophores are minimally susceptible to fluorescence quenching by Co2+. The utility of these compounds as immunodiagnostic reagents was demonstrated by encapsulating 5(6)-carboxyfluorescein trismethylolamide in haptenized liposomes which were used in an immunoassay for digoxin.