Immunoassay labels based on chemiluminescence and bioluminescence

Reagents required for reactions that produce chemiluminescence (CL) or bioluminescence (BL) may be coupled to antibodies or antigens and used as labels for immunoassay. Because methods based on CL and BL have very low detection limits, they have the potential to replace assays that currently employ radioisotopes as labels. The feasibility of several BL and CL labels has been demonstrated. To date, isoluminol derivatives have been most widely studied. Several steroid assays involving isoluminol labels have been reported, and labelled compound has been detected at levels approaching 10(17) moles. Acridinium ester-labelled compounds have also been detected at this level. In addition to systems in which the label is a reactant required for light, CL and BL can be used to analyze the amount of product generated by enzyme labels. This approach has also yielded very low detection limits. Systems have been developed using enzyme labels that catalyze formation of ATP which is then assayed by the firefly reaction or that catalyze formation of peroxide which is determined by either luminol or peroxyoxalate CL.