Preparation of a Novel pH-responsive Fluorescent Probe Based on an Imidazo[1,2-a]indole Fluorophore and its Application in Detecting Extremely Low pH in Saccharomyces cerevisiae

A novel pH-responsive probe based on an imidazo1,2-a]indole fluorophore architecture is reported. The probe was highly selective to strongly acidic pH (pK_a = 3.56) with high sensitivity and a fast response time (within 30 s). The probe did not demonstrate any fluorescence changes in the presence of interfering metal ions, and it featured excellent reversibility under strongly acidic conditions. The mechanism of detection of the probe was determined to be based on intramolecular charge transfer (ICT) at different pH. The probe was also able to be used for imaging for detecting acidic pH in Saccharomyces cerevisiae.