Photoluminescent and electrochemiluminescent detection of homocysteine based on bifunctional cyclometalated iridium(III) complex

A photoluminescent (PL) and electrochemiluminescent (ECL) chemodosimeter for homocysteine (Hcy) determination was developed based on a bifunctional cyclometalated iridium(III) complex (pba)2Ir(dcbpy). (pba)2Ir(dcbpy) was prepared by using 4′-(2-pyridyl)-benzaldehyde (pba) as main ligand and 2,2′-bipyridyl-4,4′-dicarboxylic acid (dcbpy) as ancillary ligand. The existence of aldehyde group on the main ligand and dicarboxylic acid groups on the ancillary ligand endows (pba)2Ir(dcbpy) good water solubility. Importantly, the aldehyde group on the main ligand also furnishes the chemodosimetric active site, which could react with Hcy highly in neutral buffer solution based on a unique cyclization reaction with aminoalkylthiol group to produce a binding adduct, enhancing both PL and ECL signal. The photophysical and ECL properties of (pba)2Ir(dcbpy) in the absence and presence of Hcy were investigated and the response mechanism of the luminescence enhancement was confirmed by mass spectrum. Both PL and ECL measurements exhibited good linear relationships to the Hcy with the detection of limit at micro-molar level. More significantly, (pba)2Ir(dcbpy) possessed a relatively high discriminating ability to differentiate Hcy from structurally related molecule (cysteine) under neutral buffer conditions. The PL and ECL chemodosimeter based on cyclometalated iridium(III) complex with specific active site is universal to the analysis of other targets, thus opening a new avenue for the application of cyclometalated iridium(III) complex in PL and ECL field.