Development of fast-response turn-on phosphorescent probes for biothiols based on ruthenium(II) complexes

A novel ruthenium(II) complex of [Ru(bpy)(2)(BIPP-DNBS)](ClO4)(2) (Ru-BIPP-DNBS) {bpy = 2,2'-bipyridine, BIPP-DNBS 1/4 4-bromo-2-(1H-imidazo[4,5-f][1,10] phenanthrolin-2-yl) phenyl 2,4-dinitrobenzenesulfonate} has been designed and synthesized as a fast-response turn-on phosphorescent probe for the detection of biothiols. The ruthenium(II) polypyridine complex was used as a phosphorescence reporter and 2,4-dinitrobenzenesulfonate (DNBS) was used as both a recognition unit and phosphorescence quencher. Ru-BIPP-DNBS was weakly phosphorescent owing to the effectual photoinduced electron transfer (PET) from the ruthenium(II) luminophore to the sensing group DNBS. Upon treatment with biothiols, the 2,4-dinitrobenzenesulfonyl group of Ru-BIPP-DNBS was cleaved, and the phosphorescence was "turned on", as a result of the formation of Ru-BIPP. The favorable steric interactions between the 1H-imidazo[4,5-f][1,10]phenanthroline group and ortho-2,4-dinitrobenzenesulfonate highly ameliorated the response rate of Ru-BIPP-DNBS toward biothiols, resulting in a rapid thiol-induced SNAr substitution reaction. This probe also exhibited good linearity ranges with detection limits of 0.47 mu M for cysteine and 0.27 mu M for glutathione. Furthermore, application of Ru-BIPP-DNBS for the imaging of endogenous biothiols in glioma cell samples was successfully demonstrated.