Quenching of the Electrochemiluminescence of Tris(2,2′-bipyridine)ruthenium(II)/Tri‑<i>n</i>‑propylamine by Pristine Carbon Nanotube and Its Application to Quantitative Detection of DNA

In this study, we describe the quenching of electrochemiluminescence (ECL) of tris­(2,2′-bipyridine)-ruthenium­(II)­(Ru­(bpy)₃²⁺)/tri-<i>n</i>-propylamine­(TPA) at pristine multiwall carbon nanotube (MWNT) modified glassy carbon (GC) electrode. Even though the faradic current of the Ru­(bpy)₃²⁺/TPA system and the oxidation of TPA obtained at pristine MWNT-modified GC electrode is enhanced compared with those at the bare GC electrode, the intensity of ECL produced at MWNT electrode is smaller than that at GC electrode. For testing the possible reason of quenching, a comparison of ECL behavior of Ru­(bpy)₃²⁺/TPA at pristine MWNT and acid-treated, heat-treated, and polyethylene glycol (PEG)-wrapped MWNT-modified GC electrode is studied. The results demonstrate that the oxygen-containing groups at the surface of MWNT and the intrinsic electron properties of MWNT are considered to be the major reason for the suppression of ECL. The comparison also demonstrates that this quenching is related to the distance between MWNT and Ru­(bpy)₃²⁺/TPA. Utilizing this essential quenching mechanism, a new signal-on DNA hybridization assay is proposed on the basis of the MWNT modified electrode, where single-stranded DNA (ssDNA) labeled with Ru­(bpy)₃²⁺ derivatives probe (Ru-ssDNA) at the distal end is covalently attached onto the MWNT electrode. ECL signal is quenched where Ru-ssDNA is self-organized on the surface of MWNT electrode; however, the quenched ECL signal returns in case of the presence of complementary ssDNA. The developed approach for sequence-specific DNA detection has good selectivity, sensitivity, and signal-to-background ratio. Therefore, the quenching of the ECL of Ru­(bpy)₃²⁺/TPA system by the pristine MWNT can be an excellent platform for nucleic acid studies and molecular sensing