N-heterocyclic Ir(III) complex targeting G-quadruplex structure to boost label-free and immobilization-free electrochemiluminescent sensing

Development of simple, low-cost and highly sensitive electrochemiluminescence (ECL) sensors for various targets is urgent but remains challenging. It is because most of emitters were required to be dissolved in organic solvent or immobilized at electrode's surface to display ECL emission, and suffered from complicated tagging procedures and short emission wavelength. Herein, we synthesize an iridium (III) complex (Ir-ECL) and applied it as a ECL emitter for improved target sensing. ECL emission of Ir-ECL originated from the sensitization of N-heterocyclic ligands on Ir (III). Impressively, Ir-ECL exhibited ECL emission wavelength at 590 nm, and displayed a superior intercalation ability into G-quadruplex DNA against single-stranded DNA and double-stranded DNA (dsDNA). Using such properties, Ir-ECL was applied to enzyme-free, label-free, sensitive and homogeneous ECL analysis of pesticide acetamiprid (Ace) based on aptamer-target recognition-driven hybridization chain reaction (HCR). The recognition of H1 by Ace switched HCR of H2 and H3 to generate a long-chain dsDNA with abundant G-quadruplex DNAs, in which large numbers of Ir-ECL were locked, resulting in falling diffusion toward electrode, declining ECL signal and eventually improving Ace ECL sensing.