Multiple labelling of immunoglobulin G, albumin and testosterone with a fluorescent terbium chelate for fluorescence immunoassays.

Human immunoglobulin G, human serum albumin and testosterone were labelled with the 4-aminosalicylic acid derivative of diethylenetriaminepentaacetic acid complexed with terbium ions. An exceptionally large amount of label, of the order of a few hundred moles of complex per mole of analyte, could be conjugated to the compounds tested by the use of poly-L-lysine. Self-quenching appears to be minimal, even with this high local concentration of fluorophores. The tracers were stable at 4 degrees C, and gave competitive calibration graphs at physiological concentrations.