Magnetic bead-based chemiluminescent metal immunoassay with a colloidal gold label

A novel, sensitive chemiluminescent (CL) immunoassay has been developed by taking advantage of a magnetic separation/mixing process and the amplification feature of colloidal gold label. First, the sandwich-type complex is formed in this protocol by the primary antibody immobilized on the surface of magnetic beads, the antigen in the sample, and the second antibody labeled with colloidal gold. Second, a large number of Au3+ ions from each gold particle anchored on the surface of magnetic beads are released after oxidative gold metal dissolution and then quantitatively determined by a simple and sensitive Au3+-catalyzed luminol CL reaction. Third, this protocol is evaluated for a noncompetitive immunoassay of a human immunoglobulin G, and a concentration as low as 3.1 x 10(-12) M is determined, which is competitive with colloidal gold-based anodic stripping voltammetry (ASV), colorimetric ELISA, or immunoassays based on fluorescent europium chelate labels. The high performance of this protocol is related to the sensitive CL determination of Au3+ ion (detection limit of 2 x 10(-10) M), which is 25 times higher than that by ASV at a single-use carbon-based screen-printed electrode. From the analytical chemistry point of view, this protocol will be quite promising for numerous applications in immunoassay and DNA hybridization.