A fluorescence sensor based on quantum dots for the detection of mercury ions

Mercury (II) ion (Hg2+) is one of the most widespread pollutants that poses a serious threat to public health and the environment. Research efforts on selective and sensitive detection of Hg2+, have therefore drawn considerable attention in recent years. Herein, we report a facile approach to detect Hg2+ based on quantum dots (QDs)-based nanosensor. The two single-stranded DNA (ssDNA) used in this work are modified with biotin (ssDNA-biotin) and fluorescence quencher BHQ2 (ssDNA-BHQ2). These two strands are complementary but with TTT-recognized base sequences for the Hg2+ to form a T-Hg2+-T complex. The biotin-modified ssDNA (ssDNA-biotin) is first bound to the streptavidin-modified QDs, forming a QDs/ssDNA-biotin assembly, which may be further hybridized with the ssDNA-BHQ2, producing a complex of QDs/ssDNA-biotin/ssDNA-BHQ2. The BHQ2 serves as an effective quencher of QDs with the QDs and BHQ2 in a proximity within the QDs/ssDNA-biotin/ssDNA-BHQ2 complex. The decrease of fluorescence intensity therefore serves as an indication of the presence of Hg2+. The fluorescence reduction is observed linearly correlated with the concentration of Hg2+ in the range of 1.0-20.0 nM, with a detection limit at 0.87 nM. The presented QDs-based method is expected to provide a simple, rapid and sensitive method for the detection of Hg2+ in environmental water samples.