"Switch on" fluorescent sensor for the detection of fluoride ions in solution and commercial tooth paste.

A simple and novel uracil based chemosensor (1) has been developed by one step reaction, which selectively detected F- ions via "switch on" fluorescence mode. Upon the addition of F- ion to CH3CN solution of 1, the non-fluorescent probe became highly fluorescent, showing a color change from colorless to fluorescent blue, when irradiated with 280nm light. 1H NMR studies revealed the binding sites of chemosensor 1, where C-5 hydrogen and amine hydrogens formed hydrogen bonding with F- ion. This binding mode was further confirmed using DFT calculations. Significantly, the detection limit of chemosensor 1 towards F- has been evaluated to be 47.6nM, which is lower than the maximum values of F- (1.5mg/L) ions permitted by WHO. The in-situ generated 1-F- complex has been used for secondary sensing of Ca(NO3)2, one of the component of the fertilizer. Moreover, the sensor has been successfully applied for detection of fluoride ion in commercial tooth paste.