Phenazine-Based Fluorescence Turn-Off Sensor for Fluoride: Application on Real Samples and to Cell and Zebrafish Imaging

In the present work, we report the design of a novel chemosensor 2-(1H-indole-3-yl)-1H-imidazo[4,5-b]phenazine, (R) for fluoride ion detection via a naked eye observable colour change from light yellow to brown along with 10 fold ratiometric fluorescence quenching from green to no fluorescence in a matrix containing a large number of similar toxic anions in aqueous dimethylsulfoxide (30% H2O + DMSO) solution. The sensing mechanism was ascertained to be the fluoride triggered deprotonation of imidazole as well as indole moiety of R which is supported by 1:2 saturation level equivalence of R-F-. R was fully characterized through FT-IR, H-1, C-13 NMR and HRMS. R is an effective receptor for F- within a wide range of pH that indicates its bio-compatibility. LoD and K-a for F- were found to be 1.8x10(-6) M (below 0.34 mg/Liter) and 2.7 x 10(4) M-1 respectively. The experimental observations were supported by the theoretical calculations using density functional theory. R also showed its potential practical applicability for fluoride detection in toothpaste solution. Furthermore, to prove its nontoxicity, probe R also applied to a cytotoxicity assay of HeLa cells followed by confocal fluorescence cells imaging and Zebrafish imaging experiments.