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Visible-Light Driven Photoelectrochemical Platform Based on the Cyclometalated Iridium(III) Complex with Coumarin 6 for Detection of MicroRNA.

In this study, a novel iridium(III) complex-based photoactive species, [(C6)2Ir(dppz)]+PF6-, was synthesized with coumarin 6 (C6) as a cyclometalated ligand and dipyrido[3,2-a:2',3'-c]phenazine (dppz) as an ancillary ligand. The photophysical and electrochemical properties of the complex have been investigated. It exhibits intense visible-light absorption with a molar extinction coefficient up to 9.8 × 104 M-1 cm-1 at 485 nm. The photoelectrochemical (PEC) properties of [(C6)2Ir(dppz)]+PF6- were also investigated by spin-coating on the ITO electrode. By illumination with 490 nm light, cathodic photocurrent up to 260 nA/cm2 was observed at 0 V bias potential with dissolved O2 as an electron acceptor. On the other hand, an anodic photocurrent was generated in the presence of triethanolamine (TEOA) as a sacrificial electron donor. The probable mechanisms for photocurrent generation were deduced by UV-vis absorption spectrum and cyclic voltammetry data. Adopting [(C6)2Ir(dppz)]+PF6- as photoactive intercalator, a visible-light driven PEC detection platform was successfully fabricated for microRNA detection based on an enzyme-free hybridization chain reaction as an amplification strategy. Expected, the PEC platform for microRNA-122b detection showed excellent linear response with a limit of detection down to 0.23 fM (3σ), comparable or superior to those of the reported analogous approaches. Encouragingly, this study would provide a new approach to exploit efficient photoactive species for PEC bioanalysis.