Homogeneous electrogenerated chemiluminescence immunoassay for the determination of digoxin

A novel homogeneous electrogenerated chemiluminescence immunoassay (ECLIA) for the determination of small hapten was developed. As a model system, digoxin was investigated while luminol served as luminescence label and BSA served as carrier protein. Digoxin was indirectly heavily labeled with luminol through BSA to form luminol–BSA–digoxin conjugate. The immunocomplex of luminol–BSA–digoxin conjugate with anti-digoxin antibody underwent less ECL reaction than luminol– BSA–digoxin conjugate after immunoreaction took place. Two immunoassay formats, directly homogeneous immunodetection for anti-digoxin antibody and competitive immunoassay for digoxin, were proposed to determine anti-digoxin antibody and digoxin, respectively. The anti-digoxin antibody concentration was determined in the range from 1/50,000 to 1/2000 dilution. The ECL intensity versus digoxin concentration was linear in the range from 5.0×10^-10 to 3.0×10^-8 g ml^-1. The detection limit was 2.8×10^-10 g ml^-1. The relative standard derivation for 1.0×10^-9 g ml^-1 was 5.1%. The proposed method has been applied to assay digoxin in human control serum with satisfactory results.