Electrogenerated chemiluminescence.: 83.: Immunoassay of human C-reactive protein by using Ru(bpy)32+-encapsulated liposomes as labels

Liposomes (similar to 100-nm diameter) containing Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) were prepared as an electrogenerated chemiluminescent (ECL) tag for a sandwich-type immunoassay of human C-reactive protein (CRP). Polyclonal human CRP antibodies were introduced onto liposomes and magnetic beads through biotin-streptavidin interaction. The antigen-antibody conjugates formed on addition of a CRP-containing sample were separated from unreacted species magnetically. Addition of 0.1 M tri-n-propylamine and 0.1 M phosphate buffer (pH 7.6) containing 0.1 M NaCl and 1% (v/v) Triton X-100 caused liberation of the Ru(bpy)(3)(2+) from the liposome. ECL obtained in this medium showed a detection limit of 100 ng/mL for human CRP with good linearity of ECL intensity versus antigen concentration over the range 100 ng/mL-10 mu g/mL.