A simple NIR fluorescent probe for detecting pH in actual water samples and cells

In this work, we presented a new probe (named FC) that can respond rapidly to pH. In an acidic setting, the NIR fluorescence of FC was quenched upon protonation of the pyridine moiety. FC was a weakly acidic pH probe that could accurately measure the pH within the range of 4.0 to 6.6. The probe exhibited excellent water solubility and could enable the detection of pH in aqueous systems without the need for the involvement of organic solvents. It achieved pH response through photoinduced electron transfer (PET). The fluorescence sensing mechanism and response mechanism were verified through theoretical calculations and nuclear magnetic titration. Furthermore, the probe was employed to monitor the pH level of actual water samples as well as acidity detection within cells.