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Electrochemiluminescence Immunosensor Based on Au Nanocluster and Hybridization Chain Reaction Signal Amplification for Ultrasensitive Detection of Cardiac Troponin I.

Measurement of cardiac troponin I in the blood is crucial for the early diagnosis of acute myocardial infarction. Herein, a novel and ultrasensitive electrochemiluminescence (ECL) immunosensor has been developed for determination of Cardiac troponin I (cTnI) by using Au nanoclusters and hybridization chain reaction (HCR) signal amplification. In this ECL immunosensor, Au nanoclusters were dual-labeled at each end of hairpin DNA and acted as luminophore. DNA initiator strands (T1) and secondary antibody (Ab2) were conjugated on Au nanoparticles (AuNPs) to obtain a smart probe (Ab2-AuNP-T1). In the presence of target cTnI, sandwiched immunocomplex composed of cTnI, Ab1 and Ab2-AuNP-T1 was formed. Then, the initiator strands T1 of Ab2-AuNP-T1 opened the hairpin DNA structures and triggered a cascade of hybridization events. Consequently, a large number of Au NCs were indirectly modified on the surface of electrode, which could react with the co-reactant (K2S2O8) and emit strong ECL signal. Under the optimal conditions, the immunosensor exhibited a wide detection range for cTnI from 5 fg/mL to 50 ng/mL and a low detection limit of 1.01 fg/mL (S/N = 3). Because of the excellent specificity, stability and reproducibility of the proposed ECL-HCR sensor, it has a great application prospect for cTnI detection in clinical diagnosis.