No 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) 2 Ir(dmphen)](PF 6 ), 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 E 1/2 = + 1.51 V (vs. SCE), and a reversible one-electron reduction wave at À1.29 V (vs. SCE). Typically, in the annihilation process, the ECL efficiency of this complex was 12 times higher than that of Ru(bpy) 3 2 + . More importantly, a highly sensitive ECL method for the determination of micro-RNA at the subpicomolar 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) 3 Cl 2 and [(bt) 2 Ir(dcbpy)](PF 6 ), 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.

Two cyclometalated iridium(III) complexes, (pq) 2 Ir(sa) and (pq) 2 Ir(psa), with 2-phenylquinoline (pq) as the C^N main ligand and succinylacetone (sa) or 4,6-dioxo-6-phenylhexanoic acid (psa) as the O^O ancillary ligand, were synthesized at first time. The solubility was reached down to 0.1 mM for (pq) 2 Ir(sa) and 10 M for (pq) 2 Ir(psa) in acetonitrile-water (v/v=5:95) solution. The photophysical, electrochemical and electrogenerated chemiluminescence (ECL) properties of (pq) 2 Ir(sa) and (pq) 2 Ir(psa) in acetonitrile were mainly investigated. The oxidation peak potential of (pq) 2 Ir(sa) and (pq) 2 Ir(psa) appears at +0.79V and +0.8 V vs SCE.(pq) 2 Ir(sa) and (pq) 2 Ir(psa) display orange ECL emission band with a maximum wavelength at 621 nm and 610 nm, respectively. ECL efficiencies of (pq) 2 Ir(sa) and (pq) 2 Ir(psa) in acetonitrile containing tripropylamine were calculated to be 21.3-folds and 35.4-folds higher than that of Ru(bpy) 3 2+ . It was surprised to find that small amount of water can greatly increase the ECL intensity of these two complexes in acetonitrile containing tripropylamine. The ECL methods for the determination of trace water in organic solvent were developed in the range from 0.02 to 4.0% (v/v) and 0.05 to 4.0% (v/v) with detection limit of 0.01% and 0.03% for (pq) 2 Ir(sa) and (pq) 2 Ir(psa), respectively. It was found that the O^O ancillary ligand played a key function in the water-enhanced ECL emission. A double coreactant ECL pathway is proposed for the water-enhanced ECL emission. This work demonstrates that (pq) 2 Ir(sa) and (pq) 2 Ir(psa) have lower potential and high ECL coefficient, which are promising for the effective use as ECL emitter in analytical application.