Enantioselective and Differential Fluorescence Lifetime Imaging of Nucleus and Nucleolus by the Two Enantiomers of Chiral Os(II) Polypyridyl Complex

The nucleolus is an important subnuclear structure, but very few dyes are available for nucleolar imaging. Here we show that the Λ-enantiomer of [Os(phen)2(dppz)]Cl2 can differentially distinguish the nucleolus from nucleus in living cells with tetrachlorophenolate as counteranion, while the Δ-enantiomer can do so in fixed cells by FLIM imaging. Further studies with three specific metabolic inhibitors for nucleolar protein synthesis found that the lifetime changes of the two enantiomers in the nucleolus can reflect the alteration of the cellular microenvironment, which is related to the general pathological status of the nucleolus. We then observed dynamical architecture changes of the nucleolus, chromosome and spindle apparatus during cell differentiation by these two enantiomers. The chiral Os(II) complex shows many advantages as compared to the commercially available nucleolus dye Syto 9: it displays a much larger Stokes shift value with a near-red emission and a longer lifetime, it can image spindle apparatus during mitosis, and more importantly, it is enantioselective.