In situ energy transfer quenching of quantum dot electrochemiluminescence for sensitive detection of cancer biomarkers

In this work, we develop a sensitive and selective method for the detection of a cancer biomarker (carcinoembryonic antigen, CEA) based on a new electrochemiluminescence (ECL) energy transfer mechanism, in which the energy transfer occurs from the excited quantum dots (QDs) to the in situ electro-generated quenchers. A CdTe QD-containing composite film is first deposited on the electrode followed by the conjugation of the primary antibody (Ab1) on the film. Subsequent incubation of the modified sensing electrode with CEA and the secondary antibody-alkaline phosphatase-gold nanoparticle labels (Ab2-ALP-AuNP) leads to the formation of the Ab1/CEA/Ab2-ALP-AuNPs immunocomplexes on the electrode surface. The captured ALP catalyzes the p-nitrophenyl phosphate disodium salt (p-NPP) substrate in the ECL detection buffer to p-nitrophenol (p-NP). The potential sweep on the electrode results in the oxidation of p-NP to p-benzoquinone (p-BQ) and the generation of excited QDs. The ECL emission of the excited QDs is therefore quenched through direct energy transfer from the excited QDs to p-BQ. This ECL quenching effect is significantly amplified because of the numerous ALP enzymes involved in each antibody-antigen recognition event. This proposed method of amplified quenching of QD ECL emission offers a low detection limit of 1.67 pg mL−1 for CEA. In addition, this method exhibits high reproducibility and selectivity and can also be applied to serum samples. Given these advantages, this new ECL energy transfer approach holds great promise for the detection of other biological targets and has potential applications in clinical diagnoses.