Quinoline-based ratiometric fluorescent probe for detection of physiological pH changes in aqueous solution and living cells.

Herein, a novel quinoline-based fluorescent probe DQPH has been developed for ratiometric detection of subtle pH fluctuation in biosystem. Upon altering the pH from 4.50 to 9.00, the emission spectra exhibit a large hypsochromic shift (57 nm) and the ratio of fluorescence intensity (F531 nm/F588 nm) changes from 0.30 to 1.36 with an ideal pKa value of 7.18 and a linear pH variation range of 6.35–8.00. The ratiometric response is attributed to the protonation-activable resonance charge transfer (PARCT) process, which has been proved by 1H NMR and NOESY experiment. This probe displayed good solubility, low cytotoxicity, anti-interference capability and reversible pH sensing. Furthermore, DQPH was successfully applied for monitoring pH changes in living cells.