Competitive electrochemiluminescence immunosensor based on self-deposited ultrasmall Ru nanoparticles on g-C3N4 and luminol for H-FABP detection.

Ruthenium (Ru) nanoparticles were immobilized on the g-C3N4 surface (Ru-g-C3N4), attaining lower potential electrochemiluminescence (ECL) emission of g-C3N4 and yielding an exceptional ECL signal. This enhancement was attributed to the formation of a Schottky barrier between Ru nanoparticles and g-C3N4, which mitigated electrode passivation and provides catalytically active sites that facilitated the generation of SO4∙- electrogenerated by the coreactant K2S2O8. At the same potential, luminol undergone an ECL reaction with the SO4∙- to generate luminol radicals, which can subsequently enter a competitive reaction with Ru-g-C3N4, significantly reducing the ECL intensity of Ru-g-C3N4. NH2-MIL-101(Fe) was utilized to couple with luminol (NH2-MIL-101(Fe)@Luminol), which can further enhance the quenching efficiency. This design not only efficiently quench the ECL intensity of Ru-g-C3N4, 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 (Ab2-NH2-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-1 to 50 ng mL-1, and a low detection limit of 2.43 fg mL-1 (S/N = 3) were attained.