Near-infrared lysosome pH tracker and naked-eye colorimetric nucleic acids sensor based on ruthenium complexes [Ru(bim)2(dppz)]2+ and [Ru(bim)2(pip)]2+

- Two new ruthenium complexes based pH and nucleic acids sensors have been synthesized and characterized.
- Complex 1 shown to be a naked-eye colorimetric sensor for nucleic acids.
- Complex 2 behaves as a near-infrared lysosome pH fluctuation tracker.

Two new Ru(II) complexes [Ru(bim)2(dppz)]2+1 and [Ru(bim)2(pip)]2+2 ((bim = 2,2′-biimidazole; dppz = dipyrido[3,2-a:2′,3′-c]phenazine, pip = 2-phenyl-1H-imidazo[4,5-f][1,10]phenan-throline) have been synthesized, characterized and evaluated for pH and nucleic acids detection. Both complexes respond sensitively to pH in solution with remarkable red shifts at MLCT band and display distinct color changes. Complex 1 has also shown to be an interesting naked-eye colorimetric sensor for nucleic acids with significant color change from red to yellow upon binding to DNA or RNA. Complex 2 was non-fluorescent under neutral or basic conditions, while under acidic conditions, it emits bright fluorescence at a near-infrared wavelength exhibiting a pH-dependent fluorescent turn-on property. Cell fluorescent imaging results indicate that complex 2 could cross cell membranes, localize at lysosomes, and monitor the change of intracellular pH. The large Stokes shift, low background fluorescence, and excellent stability and solubility make complex 2 a promising lysosomes pH sensor during physiological and pathological processes.

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