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Appl Biochem Biotechnol. 2014 Jan;172(2):1036-44. doi: 10.1007/s12010-013-0573-8. Epub 2013 Oct 19.

A new near-infrared neutral pH fluorescent probe for monitoring minor pH changes and its application in imaging of HepG2 cells.

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  • 1School of Chemistry and Chemical Engineering, Southeast University, Nanjing, 210096, China,


A new near-neutral pH near-infrared (NIR) fluorescent probe utilizing a fluorophore-receptor molecular framework that can modulate the fluorescence emission intensity through a fast photoinduced electron transfer process was developed. Our strategy was to choose tricarbocyanine (Cy), a NIR fluorescent dye with high extinction coefficients, as a fluorophore, and N-methylpiperazine (MP) as a receptor. The pH titration indicated that MP-Cy can monitor the minor physiological pH fluctuations with a pKa of ∼7.10 near physiological pH, which is valuable for intracellular pH researches. The probe responds linearly and rapidly to minor pH fluctuations within the range of 3.05-7.10 and exhibits strong dependence on pH changes. As expected, the real-time imaging of cellular pH and the detection of pH in situ was achieved successfully in living HepG2 cells by this probe. It is shown that the probe effectively avoids the influence of autofluorescence and native cellular species in biological systems and meanwhile exhibits high sensitivity, good photostability, and excellent cell membrane permeability.

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