A reversible near-infrared pH probes for optical measurements of pH in complete water system and living cells

• The new probe hadgood photostability and favorable response reversibility.
• Cy-H displayed multiple color change of yellow-green-blue at different pH values.
• The pH sensor had low cytotoxicity and good cellularimaging ability.
• Cy-H was conducive to longtime monitoring of pH changes without interference.

The intracellular pH value controls many aspects of cell metabolism and is considered as an integral part of many metabolic reactions by maintaining the structure and function of nearly all proteins. Detection of pH fluctuation covering the whole intracellular pH window including both neutral and acidic is essential but challenging and still needs more sensitive pH probes. We have synthesized a new near-infrared fluorescent and colorimetric probe based on cyanine dye, which can be used for monitoring the pH fluctuation. The probe has a good water solubility, excellent photostability, reversibility, low cytotoxicity and exhibits a good performance to detect pH fluctuation in both solution and live cells. Upon incubation with live cells, it responds sensitively to low pH value in cell medium by exhibiting bright red fluorescence. On the contrary, the fluorescence intensity of probe seems to be very weak in neutral cellular environment. The satisfactory results show that the probe was a highly sensitive pH probe in living cells and further demonstrate its promising biological applications.

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