Selective and sensitive mercuric (ii) ion detection based on quantum dots and nicking endonuclease assisted signal amplification.

This work reports a novel signal amplification method for Hg(2+) detection based on quantum dots (QDs) and nicking endonuclease (NEase). In this assay, streptavidin-coated QDs were conjugated to biotinylated hairpin-shaped probe A which was modified with a quencher BHQ-2. The fluorescence of the QDs was quenched by BHQ-2 through FRET quenching. In the presence of Hg(2+), probe B hybridized with the loop of probe A due to specific binding between thymine-thymine mismatches and Hg(2+), thus probe A was opened. Then NEase recognized specific nucleotide sequences and cleaved probe A. After the dissociation of probe A fragments, the distance between QDs and BHQ-2 increased, which led to increase of QDs fluorescence. The released Hg(2+) and probe B could hybridize with another probe A to start a new cycle, therefore a remarkable signal amplification was achieved. Under optimal conditions, the detection limit of this assay was 8.0×10(-10)mol L(-1).