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

Abstract

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 dot (QD)-based nanosensor. The two single-stranded DNA (ssDNA) used in this work are modified with biotin (ssDNA–biotin) and fluorescence black hole 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 nmol/L, with a detection limit at 0.87 nmol/L. The presented QD-based method is expected to provide a simple, rapid, and sensitive method for the detection of Hg2+ in environmental water samples.