Chemiluminescent dual-enzyme immunoassays capable of simultaneously quantifying carbohydrate antigen 19-9 and carcinoma embryonic antigen in a sample.

Using the internal chemiluminescence resonance energy transfer (Inter-CRET) of luminescent dye and the high-energy intermediate formed in 1,1'-oxalyldiimidazole chemiluminescence (ODI-CL) reaction, we developed for the first time dual-enzyme immunoassays operated with alkaline phosphatase (ALP) and horseradish peroxidase (HRP) for the simultaneous quantifications of carbohydrate antigen 19-9 (CA19-9) and carcinoma embryonic antigen (CEA) in a sample. Fluorescein formed from the ALP enzyme immunoassay emits green light in ODI-CL reaction, while resorufin formed from the HRP enzyme immunoassay emits red light. Green and red CL lights emitted in a detection cell were measured individually with two photomultiplier tubes with an optical filter capable of sensing green or red emission without interferences. The limits of detection for CA 19-9 (0.09 U/ml) and CEA (0.11 ng/ml) determined using the accurate and reproducible dual-enzyme immunoassays were as low as those calculated using the conventional single-enzyme immunoassays capable of sensing CA 19-9 or CEA in a sample. In conclusion, we confirmed that the highly selective dual enzyme immunoassays can be applied as a new analytical method capable of early diagnosing and monitoring colon and pancreatic cancers with the simultaneous analyses of CA 19-9 and CEA.