Highly sensitive electrochemiluminescence immunoassay using the ruthenium chelate-labeled antibody bound on the magnetic micro beads

The newer electrochemiluminescence (ECL) immunoassay system was established by using both an antibody coated on paramagnetic micro-beads (Capt-MB) as a carrier of the immunoassay and an antibody labeled with ruthenium(II) tri s-bipyridine-NHS (Ru-Ab). The ECL excitations were designed to be generated upon the surface of the working electrode which collected the reacted Capt -MB by magnetic force. As a model of the immunoassay, the reaction between alphafetoprotein (AFP) and anti-AFP antibodies was used in accordance with the so-called sandwich method, where the sandwich conformation of AFP-(Ru-A b) was made on the surface of the Capt-MB. The ECL immunoassay system revea led the following results: a) the ECL signal intensity was obtained in prop ortion to the AFP concentration of each specimen; b) the dynamic range of t his ECL immunoassay system was er;tended to 10000 times of magnitude in the 2-step assay; and c) the detection sensitivity reached to the level of 5 p g/ml in the AFP concentration after 15 min in the 1-step immunoassay.