“Turn off-on” phosphorescent sensor for biothiols based on a Ru-Cu ensemble

Glutathione (GSH), cysteine (Cys), and homocysteine (Hcy) are three major biothiols, which play key roles in various biological systems. Accordingly, the development of phosphorescent probe of biothiols has attracted great attention in clinical applications. Here we report a ruthenium polypyridyl complex (1), which shows large phosphorescence quenching with 2.0 equivalents of Cu2+ ions. The non-phosphorescent 1−Cu ensemble sensor is formed and further applied to detect biothiols in living cancer cells. Among the various amino acids, GSH, Cys and Hcy induce distinct turn-on phosphorescence with high selectivity and insensitivity to biological relevant pH range and other proteins. As we know, this is the first report that Ru−Cu ensemble is used for probing endogenous thiols in the living cells.