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

Abstract

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 (H₁ and H₂) and acted as the 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, the 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 the electrode, which could react with the coreactant (K₂S₂O₈) and emit a 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.