Electrochemiluminescent immunoassay for insulin by using a quencher pair consisting of CdS:Eu nanoclusters loaded with multiwalled carbon nanotubes on reduced graphene oxide nanoribbons and gold nanoparticle-loaded octahedral CuO.

A sensitive electrochemiluminescence (ECL) immunosensor was constructed for detection of insulin. It is based on the quenching effect of octahedral cuprous oxide decorated with gold nanoparticles (CuO@Au NPs). A composite constructed from multiwalled carbon nanotubes/reduced graphene oxide nanoribbons provides a large specific surface that promotes electron transfer on the surface of electrodes. In parallel, CdS nanoclusters were loaded with europium(III) to get CdS:Eu NCs. The Eu(III) ions exert a large enhancement in ECL intensity of the CdS NCs. CuO is biocompatible and has a large specific surface. It was used as a quencher for the ECL immunosensor. If Au NPs are loaded onto CuO, the green fluorescence of the CdS NCs (with emission peaks at 525 nm) is quenched. The CuO@Au NPs also can be employed as a label for the secondary antibodies (Ab) to improve the sensitivity of the ECL immunosensor. The assay works in the 0.5 pg·mL to 50 ng·mL insulin concentration range and has a detection limit of 40 fg·mL. Graphical abstract The multiwalled carbon nanotubes/reduced graphene oxide nanoribbons (MWCNT/rGONRs-CdS: Eu NCs) was used as substrate. Europium(III) (Eu) improves the ECL intensity of CdS NCs. The synergistic effect between CuO and Au NPs decreases the electrochemiluminescence of MWCNTs/rGONRs-CdS:Eu NCs.