An ultrasensitive electrochemiluminescence immunoassay based on supersandwich DNA structure amplification with histidine as a co-reactant

Here we report a novel electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of carcinoembryonic antigen (CEA) via histidine labeled supersandwich DNA structure to amplify the ECL signal. Histidine is an α-amino acid with an imidazole group, which can act as a co-reactant of tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy)3(2+)) to amplify ECL signal. To the best of our knowledge, this is the first time to use histidine as co-reactant of Ru(bpy)3(2+) for signal amplification. The ECL substrate is fabricated by locating the complex of Pt nanoparticles (PtNPs) and Ru(bpy)3(2+) (Ru-PtNPs) on Nafion modified electrode surface. In the presence of antigens, the sandwiched immunocomplex can be formed between the primary antibodies on the ECL substrate and the secondary antibodies on the gold nanoparticles. The carried auxiliary probe I trigger a cascade of hybridization events between alternating auxiliary probe I and histidine-modified auxiliary probe II to form the long DNA concatamers. Thus the long DNA concatamers contain multiple histidine-modified auxiliary probe II, which accordingly achieve significant signal amplification. As a result, the sensitivity of proposed immunosensor for CEA detection is improved, the linear range is from 0.1 pg mL(-1) to 100 ng mL(-1) with a low detection limit of 33.3 fg mL(-1). Moreover, with the satisfying stability, selectivity and reproducibility, the proposed supersandwich immunoassay performs good promise in clinical detection.