Development of Visible-Light Induced Photoelectrochemical Platform Based on Cyclometalated Iridium(III) Complex for Bioanalysis

The performance of the photoelectrochemical (PEC) bioanalysis relies closely on the properties of the used photoactive species. In this study, a visible-light induced PEC active species, [(C6)₂Ir(dcbpy)]⁺PF₆^- (C6 = coumarin 6, dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid) was prepared based on C6 with the stronger absorbance in the visible region. The as-prepared complex was characterized by ¹H NMR, UV-visible absorption and cyclic voltammetry. It exhibits intense absorption in visible region at 480 nm with a molar extinction coefficient (ε) of more 40000 M^-1 cm^-1, which is approximately twice that of Ru(bpy)₃²⁺. The PEC behaviors of the iridium(III) complex were investigated through covalently attaching to the ITO electrode. Induced by visible light, a large and stable cathodic photocurrent can be observed when dissolved O₂ is served as a sacrificial electron acceptor. Also probable mechanisms of photocurrent generation are deduced. Employing [(C6)₂Ir(dcbpy)]⁺PF₆^- as signal reporter, the Au NPs-based nanoprobe was constructed and successfully applied to assembly PEC platform based on the Exo III-assisted recycling amplification for bioanalysis. With thrombin as a model analyte, the PEC platform was found to be logarithmically proportional to thrombin concentrations across the range from 20 fM to 10 pM with fine selectivity, indicating excellent PEC properties of the synthesized Ir(III) complex and enormous potential for PEC bioanalysis.