An Indole-Based Chemosensor for the Detection of Fluoride Ion and Use In Bioimaging

A new indole-based chemosensor, called FL ((E)-N'-(3-chloro2-hydroxybenzylidene)-1H-indole-2-carbohydrazide) capable of recognizing F- ions and exhibiting a turn-on fluorescence response, was synthesized and tested. FL showed a high fluorescence enhancement in the presence of F- ions in a solution of CH3CN-phosphate and buffer solution (PBS) (99:1, v/v) with a significant color change (from colorless to yellow). FL had a good linear relationship with F- from 0 to 11.85 mu M and a detection limit up to 3.2 nM. The Job plot indicated that FL formed a compound with F- ions in a 2:1 ratio and the binding constant was calculated to 3.6 x 10(4) M-2. The proposed bonding mechanism between FL and the F- ion was speculated as hydrogen bonding by O-H center dot center dot center dot F. Results of fluoride ion detection in water samples and cell imaging demonstrated that FL has the potential application to investigate biological processes involving F- ion within living cells.