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) tris-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 alpha-fetoprotein (AFP) and anti-AFP antibodies was used in accordance with the so-called sandwich method, where the sandwich conformation of AFP-(Ru-Ab) was made on the surface of the Capt-MB. The ECL immunoassay system revealed the following results: a) the ECL signal intensity was obtained in proportion to the AFP concentration of each specimen; b) the dynamic range of this ECL immunoassay system was extended to 10000 times of magnitude in the 2-step assay; and c) the detection sensitivity reached to the level of 5 pg/ml in the AFP concentration after 15 min in the 1-step immunoassay.

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