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 Cu₂O

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 (Cu₂O@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. Cu₂O is biocompatible and has a large specific surface. It was used as a quencher for the ECL immunosensor. If Au NPs are loaded onto Cu₂O, the green fluorescence of the CdS NCs (with emission peaks at 525 nm) is quenched. The Cu₂O@Au NPs also can be employed as a label for the secondary antibodies (Ab₂) to improve the sensitivity of the ECL immunosensor. The assay works in the 0.5 pg·mL⁻¹ to 50 ng·mL⁻¹ insulin concentration range and has a detection limit of 40 fg·mL⁻¹.

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