Two water-soluble near-infrared luminescent probes, which possess both conventional intense Stokes fluorescence and unique single-photon frequency upconversion luminescence (FUCL) have been developed for sensitive and selective detection of pH changes in live cells. The water solubility and biocompatibility of these probes have been achieved by introducing mannose residues through 2,2’-(ethylenedioxy)diethylamine tethered spacers to a conventional near-infrared fluorescence and FUCL organic fluorophore. The probes are colorless and non-fluorescent with closed spirocyclic amide structures at a pH higher than 7.4. However, they sensitively respond to acidic pH values with a significant absorbance increase at 714 nm, both conventional near-infrared florescence and FUCL enhancements at 740 nm with excitation wavelengths of 690 nm and 808 nm, respectively, because the acidic pH causes drastic structural changes of the probes from a non-fluorescent ring-closed spirocyclic amide form to a fluorescent ring-opened spirocyclic amide form. The probes hold a variety of advantages such as high sensitivity to pH, excellent reversibility and selectivity to pH over metal ions, low auto-fluorescence background, excellent photostability, good cell membrane permeability, and low cytotoxicity. They have been successfully used to visualize intracellular lysosomal pH changes in live cells by monitoring both conventional near-infrared fluorescence and FUCL changes.<br/>

Water-soluble conventional and upconversion near-infrared luminescent probes for sensitive detection of pH changes in living cells

254th National Meeting (2017)

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