Two ratiometric near-infrared fluorescent probes have been developed for sensitive detection of pH in live cells by covalently attaching BODIPY donors to near-infrared Rhodamine counterpart acceptors via an ethynyl connection.  At neutral and basic pH values, only BODIPY donors in the probes show their absorption peaks at 400 nm and 571 nm, and a fluorescence peak at 595 nm because the Rhodamine counterpart acceptors retain their closed spirocyclic forms. However, decrease of pH from 7.4 to 4.0 results in a new absorption peak at 734 nm and a new near-infrared fluorescence peak at 760 nm appears at excitation of 540 nm because acidic pH leads to ring opening of the spirocylic form of the acceptor.  In addition, fluorescence peak of the acceptors at 760 nm increases significantly while fluorescence peak of BODIPY donors at 595 nm decreases correspondingly because of highly efficient energy transfer through the bonds from the donors to the acceptors when pH is changed from 7.5 to 4.0.  Furthermore, strong unique single-photo frequency upconversion luminescence at 760 nm is also observed in acidic pH condition at excitation of 830 nm.  The probes have been successfully applied to visualize intracellular lysosomal pH changes in live cells by measuring visible and near-infrared fluorescence changes.

Ratiometric near-infrared fluorescent probes for sensitive detection of pH in live cells

254th National Meeting (2017)

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