Chemiluminescence energy transfer: a new technique applicable to the study of ligand--ligand interactions in living systems

Chemiluminescent molecules can be readily detected in the range 10 −15 to 10 −18 mol, and potentially at least down to 10 −20 mol reacting/s. The chemiluminescent compound aminobutylethylisoluminol (ABEI) and its isothiocyanate derivative have been synthesized. The ABEI was coupled to rabbit immunoglobulin and cyclic AMP. These labeled antigens were stable for at least 9 months and were used to establish chemiluminescent immunoassays. When these chemiluminescent-labeled antigens bound to their respective fluorescein-labeled antibodies, a wavelength shift towards the green was detected in the chemiluminescence. This was due to chemiluminescence energy transfer and used to establish an homogeneous immunoassay which could measure these antigens in biological samples at least as sensitively as conventional radioimmunoassays.