Turn-on Luminescent Probe for Cysteine/Homocysteine Based on a Ruthenium(II) Complex

A unique ruthenium(II) complex, tris(4-methyl-2,2'-bipyridy1-4'-carboxaldehyde)Ru(II) hexafluorophosphate [Ru(CHO-bpy)(3)](PF6)(2), has been designed and synthesized as a highly sensitive and selective luminescence probe for the recognition and detection of cysteine (Cys) and homocysteine (Hcy). The almost non-luminescent probe can rapidly react with Cys and Hcy to yield the corresponding thiazolidine and thiazinane derivatives, accompanied by the remarkable luminescence enhancement and a large blue-shift of the maximum emission wavelength from 720 to 635 nm. The dose-dependent luminescence enhancement of the probe shows a good linearity in the Cys/Hcy concentration range of 15 to 180 mu M with the detection limits of 1.41 mu M and 1.19 mu M for Cys and Hcy, respectively. Furthermore, the luminescence response of the probe is highly specific to Cys/Hcy only even in the presence of various amino acids, protein, and DNA. The results of this work not only demonstrate the efficacy and advantages of the Ru(II) complex-based luminescence probe for the sensitive and selective detection of Cys/Hcy but also provide a useful strategy for the rational design of Ru(II) complex-based luminescence probes for various biological molecules.