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

Abstract 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 (O 2 ) 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) 3 2+ ) 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-PtCu 3 -Ab 2 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 H 2 O 2 which could be catalyzed by PtCu 3 alloy NCs to in situ generate O 2 , 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).