Cyclometalated Iridium-Complex-Based Label-Free Supersandwich Electrogenerated Chemiluminescence Biosensor for the Detection of Micro-RNA

Abstract

The synthesis and characterization of compounds as electrogenerated chemiluminescence (ECL) reagents are crucial in fundamental research for ECL biosensors. In this work, a new cyclometalated iridium(III) complex, [(bt)2Ir(dmphen)](PF6), was synthesized by using 2-phenylbenzothiazole (bt) as the C^N main ligand and 5,6-dimethyl-1,10-phenanthroline (dmphen) as the N^N ancillary ligand. The photophysical, electrochemical, and ECL properties of this complex were extensively studied in acetonitrile solvent and aqueous solution. This complex displayed yellow-green photoluminescence with a maximum wavelength at 522 nm, a reversible one-electron oxidation wave at E1/2=+1.51 V (vs. SCE), and a reversible one-electron reduction wave at −1.29 V (vs. SCE). Typically, in the annihilation process, the ECL efficiency of this complex was 12 times higher than that of Ru(bpy)32+. More importantly, a highly sensitive ECL method for the determination of micro-RNA at the sub-picomolar level was developed on basis of employing this complex as an ECL intercalator and signal amplification by using the supersandwich model. Compared with Ru(phen)3Cl2 and [(bt)2Ir(dcbpy)](PF6), this complex showed a relatively low background and the highest increased ratio as an ECL intercalator in the developed system. The increased ECL intensity was directly proportional to the concentration of the micro-RNA in the range of 0.1 to 10 pM, with a detection limit of 13 fM. The developed method can effectively discriminate target micro-RNA122 from two-base mismatched micro-RNA122. This work demonstrates that this cyclometalated iridium(III) complex is an effective alternative intercalator for ECL determination of the micro-RNA. It is expected that this complex will be extended to design various analytical platforms for the detection of diverse analytes such as DNA/RNA, DNAzyme/target, and aptamer/targets.