A sensitive electrochemiluminescence immunosensor for cardiac troponin I detection based on dual quenching of the self-enhanced Ru(II) complex by folic acid and in situ generated oxygen

A sensitive electrochemiluminescence (ECL) immunosensor was constructed for cardiac troponin I (cTnI) detection by dual quenching effect of folic acid (FA) and in situ generating oxygen (O2) toward the ECL signal of Ru-PAMAM/AuNPs complex. Firstly, polyamidoamine (PAMAM) was linked with tris (4,4′-dicarboxylicacid-2,2′-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)32+) via amide bond, and immobilized on gold nanoparticles (AuNPs) by Au-N bond. Then, a strong initial ECL signal was obtained when the Ru-PAMAM/AuNPs complex was assembled onto the modified electrode surface. Furthermore, a novel dual quenching effect of GOD-FA-PtCu3-Ab2 bioconjugate upon the Ru-PAMAM/AuNPs complex-based ECL system was designed to greatly enhance the sensitivity of immunosensor, which was outlined as follows: (1) FA oxidized the excited state PAMAM-Ru(II)* to PAMAM-Ru(III) making the ECL signal quench; (2) Glucose oxidase (GOD) catalyzed the oxidation of glucose to produce H2O2 which could be catalyzed by PtCu3 alloy NCs to in situ generate O2, leading to further quenching of the ECL signal. As a results, the proposed ECL immunosensor exhibited a wide linear detection range of 0.1 pg/mL to 0.2 ng/mL and a low detection limit of 12 fg/mL (S/N = 3).