Chemiluminescent enzyme immunoassay for alpha‐fetoprotein using β‐D‐galactosidase as label and 5‐bromo‐4‐chloro‐3‐indolyl‐β‐D‐galactopyranoside as substrate

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Abstract
We developed a sensitive chemiluminescent sandwich‐type enzyme immunoassay (CLEIA) of alpha‐fetoprotein (AFP) using b̃‐D‐galactosidase (b̃‐gal) as a label and 5‐bromo‐4‐chloro‐3‐indolyl‐b̃‐D‐galactopyranoside as a substrate. The CL‐EIA for AFP was performed using two monoclonal antibodies, one antibody is labelled with b̃‐gal, the other is coated onto the inside surface of a polystyrene tube. The detection limit for AFP was 0.5 ng/mL, equivalent to 10 pg/assay tube. The coefficient of variation for within and between assay imprecision were 2.0%−4.9% (n = 10) and 4.4%−9.8% (n = 5), respectively. AFP values in serum determined by this method correlated well with those obtained by radioimmunoassay (n = 26, r = 0.99). This sensitive AFP assay can be performed within 4 h and can be used as a routine assay in clinical diagnosis.