Competitive electrochemiluminescence immunosensor based on self-deposited ultrasmall Ru nanoparticles on g-CN and luminol for H-FABP detection.

Ruthenium (Ru) nanoparticles were immobilized on the g-CN surface (Ru-g-CN), attaining lower potential electrochemiluminescence (ECL) emission of g-CN and yielding an exceptional ECL signal. This enhancement was attributed to the formation of a Schottky barrier between Ru nanoparticles and g-CN, which mitigated electrode passivation and provides catalytically active sites that facilitated the generation of SO electrogenerated by the coreactant KSO. At the same potential, luminol undergone an ECL reaction with the SO to generate luminol radicals, which can subsequently enter a competitive reaction with Ru-g-CN, significantly reducing the ECL intensity of Ru-g-CN. NH-MIL-101(Fe) was utilized to couple with luminol (NH-MIL-101(Fe)@Luminol), which can further enhance the quenching efficiency. This design not only efficiently quench the ECL intensity of Ru-g-CN, but it could also be utilized for immobilizing the secondary antibody of heart-type fatty acid binding protein (H-FABP) which is a biomarker for acute myocardial infarction. By undergoing an immune reaction with the antigen H-FABP, the labels (Ab-NH-MIL-101(Fe)@Luminol) were immobilized onto the electrode surface, and their quantity on the electrode surface changes accordingly with variations in antigen concentrations. Based on this principle, a competitive ECL immunosensor was constructed for detecting H-FABP. The range of detection extended from 5.0 fg mL to 50 ng mL, and a low detection limit of 2.43 fg mL (S/N = 3) were attained.