Colorimetric Chemosensor and Turn on Fluorescence Probe for pH Monitoring Based on Xanthene Dye Derivatives and its Bioimaging of Living Escherichia coli Bacteria

A new turn on fluorescence probe based on 3′,6′-dihydroxy-6-methyl-2-((pyridin-2-ylmethylene)amino)-4-( p -tolyl)spiro[benzo[f]isoindole-1,9′-xanthen]-3(2H)-one ( BFFPH ) derived from benzo[f]fluorescein was prepared. Full characterization of the prepared probe using spectroscopic analysis was described such as IR, NMR and MS spectra. The sensitivity of BFFPH for monitoring of pH change in alkaline medium was studied. BFFPH exhibited a high sensitivity to alkaline pH by two pKa values at 8.82 and 10.66 in UV/vis spectroscopy titration. The pH monitoring was studied in broad range of pH values (2.5–12.2) at two pKa values at 8.72 and 10.73 by recording the effect of pH on the fluorescence intensity of BFFPH . The acid-base reversibility character of the probe was investigated as well as the effect of the pH change on the fluorescence quantum yield. The application of the prepared BFFPH probe for detection of living Escherichia coli (E. coli ) bacteria using confocal fluorescence microscope was investigated.