A novel electrochemiluminescent detection of protein biomarker using l-cysteine and in situ generating coreactant for signal amplification

In this work, a novel peroxydisulfate electrochemiluminescence (ECL) strategy based on a sandwich-type immunosensor for sensitive detection of carcinoembryonic antigen (CEA) was developed. The primary antibody anti-CEA (Ab1) was immobilized onto Au nanopractices (AuNPs) electrodeposited onto the electrode, which have large surface area and high electrical conductivity. Then, l-cysteine (l-Cys) and AuNPs functionalized multiwalled carbon nanotubes (MWCNTs) were synthesized to act as the platform for immobilization glucose oxidase (GOD), horseradish peroxidase (HRP) and secondary antibody (Ab2). The CEA antigen and MWCNTS-l-Cys-AuNPs@GOD-HRP-labeled Ab2 were then successively conjugated to form sandwich-type immunocomplexes through the specific interaction between antigen and antibody. The ECL signal amplification was significantly improved due to the synergistic effect of AuNPs and l-Cys. Furthermore, when proper amounts of d-glucose were added in the detection solution, GOD catalyzed the oxidation of glucose to generate H2O2, which could be further catalyzed by HRP to generate O2 for the signal amplification. The developed ECL immunosensor exhibited high sensitivity and specificity for the detection of CEA and responded linearly to the clinically relevant concentration of CEA from 0.02 to 80 ng mL−1 with a low detection limit of 0.67 pg mL−1. The present work provided a promising technique for highly sensitive bioassays applied in clinical detection.