Highly efficient electrochemiluminescence of ruthenium complex-functionalized CdS quantum dots and their analytical application

The electrochemiluminescence (ECL) method has attracted increasing attention in analytical fields. However, ECL luminophores with high ECL efficiency both at positive and negative potentials still remain rare. Herein, we synthesized ruthenium complex-functionalized CdS quantum dots (QDs) with high ECL efficiency both at positive and negative potentials in aqueous solution. CdS QDs were chosen as the ECL donor while bis(2,2'-bipyridine)-(5-aminophenanthroline)ruthenium bis(hexafluorophosphate) (Ru-NH2) was employed as the ECL acceptor. Ru-NH2 was covalently coupled to the surface of CdS QDs via diazonium salt chemistry to form CdS-Ru nanoparticles. ECL resonance energy transfer (ECL-RET) occurred inside the CdS-Ru nanoparticles and strong ECL emissions were obtained from CdS-Ru nanoparticles at both positive potential in the presence of tri-n-propylamine and at negative potential in the presence of peroxydisulfate. Further, the combination of the excellent recognition ability of the aptamer and the good ECL behavior of CdS-Ru nanoparticles, as a proof-of-concept, showed that two sensitive ECL methods for the detection of thrombin were readily achieved under different ECL measurement conditions with a low detection limit of 0.6 pM and 0.7 pM. This work demonstrates that CdS-Ru nanoparticles with intramolecular ECL-RET are good ECL luminophores in the sensitive detection of targets, which is promising in multiple assays with spectrum-resolved and potential-resolved possibility for biological applications.