Ultrasensitive electrochemiluminescent detection of cardiac troponin I based on a self-enhanced Ru(II) complex

To promote the luminous efficiency of luminophore, traditional electrochemiluminescence (ECL) immunoassay usually adopts the adding of coreactant into testing solution. However, many adverse micro-environmental factors in the solution are a limiting factor in ECL analytical techniques and received extensive attention. In our work, a self-enhanced ECL luminophore was synthesized by combining the coreactant (l-cysteine) and the luminophor (tris (4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)3(2+))) to form one Ru(II) complex and was applied to fabricate a reagentless immunosensor for the detection of cardiac troponin I (cTnI) for the first time. Herein gold nanorods (AuNRs), due to their high specific surface area and good electrocatalytic ability, were used as carriers for the immobilization of Ru(II) complex and cTnI antibody to obtain the Ab2 bioconjugates as signal labels. The application of the self-enhanced Ru(II) complex not only avoided the addition of any coreactant into testing solution for simplifying the operation, but also achieved the intramolecular reaction for improving the ECL signal due to shorter electron transfer path and less energy loss. In view of these advantages, the proposed immunosensor achieved a wide linear range from 0.25 pg/mL to 0.1 ng/mL with an impressive detection limit of 0.083 pg/mL for cTnI (S/N=3).