An unusually acidic environment around living cells may be an indicator that processes associated with disease are taking place in the vicinity. Of course there’s a myriad of other biological variables related to the cellular pH. To measure the cellular pH levels, fluorescent dyes exist that glow when illuminated by a specific wavelength of light and that find themselves in an environment that has a certain pH range. A problem with these dyes is that they fluoresce when energized by high frequency light that can damage the surrounding cells. Researchers at Michigan Technological University have now developed a new fluorescent dye to measure the pH that is excited by light in the near-infrared, and even lower, range.
The new water-soluble luminescent probes emit light when they’re themselves illuminated by near-infrared light, but they are also detectable using single-photon frequency up-conversion luminescence (FUCL) when an even weaker frequency of light is used to excite them.
Some details from the study abstract in journal ACS Sensors:
The water solubility and biocompatibility of these probes were achieved by introducing mannose residues through 2,2′-(ethylenedioxy)diethylamine tethered spacers to a near-infrared conventional fluorescence (CF) and FUCL organic fluorophore. At a pH higher than 7.4, the probes have ring-closed spirocyclic lactam structures, thus are colorless and nonfluorescent. Nevertheless, they sensitively respond to acidic pH values, with a drastic structural change to ring-opened spirocyclic lactam forms, which cause significant absorbance increases at 714 nm. Correspondingly, their near-infrared CF and FUCL intensities at 740 nm are also significantly enhanced when excited by 690 and 808 nm, respectively. The probes hold a variety of advantages such as high sensitivity, excellent reversibility and selectivity to pH over metal ions, low cellular autofluorescence background interference, good cell membrane permeability and photostability, as well as low cytotoxicity. Our results have successfully proven that these probes can visualize intracellular lysosomal pH changes in live cells by monitoring both near-infrared CF and FUCL changes.
Via: Michigan Tech…