Quenching of tungsten-based polyoxometalate nanoclusters on electrochemiluminescence emission of luminol loaded CeVO/Au for immunoassay of protein.

A quenching-typed electrochemiluminescence (ECL) immunosensing method was proposed for protein detection by the redox reaction of tungsten-based polyoxometalate nanoclusters (W-POM NCs) with free radical (O) as the intermediate of co-reactant HO. The immunosensor was constructed by co-immobilizing luminol loaded CeVO/Au nanohybrids and capture antibody on an indium tin oxide electrode, which showed strong ECL emission in the presence of HO due to the catalysis of CeVO/Au toward its electro-oxidation to produce O via the reversible conversion between Ce and Ce. The W-POM NCs were encapsulated in the uniformly sized amino-silica nanosphere (SiO) to act as a label (W-POM@SiO) of the secondary antibody. Upon the sandwich-typed immunoreactions with the target, the W-POM NCs were introduced onto the immunosensor surface to reduce O, and thus quenched the ECL emission of luminol-HO system. Using neuron-specific enolase (NSE) as a target, the proposed method showed a detection limit of 0.19 pg/mL and detectable range of 0.5 pg/mL to 18 ng/mL. The excellent performance of the proposed "ON-OFF" strategy demonstrated that the W-based quenching offers an effective tag for immunoassay of protein biomarkers.