Electrochemiluminescent “turn-on” chemosensor based on the selective recognition binding kinetics with glutathione

Recently, there have been urgent demands for decentralized, point-of-care (POC) diagnostics for digital healthcare, telemedicine, and individual self-assessment. A chemosensor producing electrochemiluminescence (ECL) upon molecular recognition is distinctly advantageous as it offers sensitive target signals without the need for bulky instrumentation and highly trained personnel. Herein, we report an Ir(III)-based chemosensor (1) that selectively generates ECL signal only at the content of glutathione (GSH) among various interferences. Our sensing strategy is based on the binding stability between the 1 and GSH. 1 possesses the terpyridine-Cu(II) branch as a recognition unit undergoing complexation reaction by various biothiols in human serum. The binding motif of 1 is structurally less selective and weak to be easily broken by dissolved oxygen. However, 1 exhibits long-lasting stability only with GSH enabling quantitative chemosensing for GSH. Time-resolved fluorescent assay along with the NMR and mass spectrometry study reveals that GSH permits the stable complexation with 1. The ECL approach additionally provides high detection sensitivity and selectivity towards GSH, which is challenging in fluorescence assay. Various coreactant ECLs, including oxalate (C2O42-), tri-n-propylamine (TPA), and peroxydisulfate (S2O82-), were investigated to find optimal conditions for the ECL chemosensing. After 15 min incubation in a 40 μL deproteinized serum sample, 1 successfully reports the GSH content by yielding an efficient ECL signal in a compact, homemade ECL device. The ECL “turn-on” signal provides a linear correlation only to the GSH level, which is 0–25 μM under a detection limit of 1.47 μM.