DNA-templated copper nanoclusters as a fluorescent probe for fluoride by using aluminum ions as a bridge.

A selective fluorescent on-off-on probe has have designed for the detection of fluoride (F) ions based on DNA-templated copper nanocluster (CuNCs) and by using aluminum(III) ions as a bridge. A 40-mer polythymine acts as a template for the reduction of Cu(II) to Cu(0) by ascorbic acid. This result is the formation of red fluorescent CuNCs, with excitation/emission peaks at 340/640 nm. After addition of Al ions, the fluorescence of CuNCs is quenched because the interaction of Al and DNA disturbs the formation of DNA-templated CuNCs. Fluorescence is restored on addition of fluoride to the system. This is due to the desorption of Al from the DNA and the formation of the Al(OH)F complex. This system displays a fast fluorometric response to fluoride, with high selectivity over other anions. Fluorescence increases linearly in the 2 to 150 μM F concentration range, and the detection limit is 1.0 μM. This probe has been successfully used for the detection of F ions in four brands of toothpaste. The method is rapid, cost-effective, selective, and does not require toxic solvents and reagents. Graphical abstract Schematic presentation of a method for fluorometric determination of fluoride by using DNA-templated copper nanoclusters (CuNCs) and using aluminum(III) as a bridge. The red fluorescence of the CuNCs is quenched in the presence of Al(III) ions but restored after addition of fluoride.