Quenching of tungsten-based polyoxometalate nanoclusters on electrochemiluminescence emission of luminol loaded CeVO4/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 (O2•-) as the intermediate of co-reactant H2O2. The immunosensor was constructed by co-immobilizing luminol loaded CeVO4/Au nanohybrids and capture antibody on an indium tin oxide electrode, which showed strong ECL emission in the presence of H2O2 due to the catalysis of CeVO4/Au toward its electro-oxidation to produce O2•- via the reversible conversion between Ce3+ and Ce4+. The W-POM NCs were encapsulated in the uniformly sized amino-silica nanosphere (SiO2) to act as a label (W-POM@SiO2) of the secondary antibody. Upon the sandwich-typed immunoreactions with the target, the W-POM NCs were introduced onto the immunosensor surface to reduce O2•-, and thus quenched the ECL emission of luminol-H2O2 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.