Dulplex analysis of mercury and silver ions using a label-free fluorescent aptasensor

Label-free Hg2+ aptamer was used as a sensing element and the PicoGreen dye was specific to ultra-sensitive double-stranded DNA (dsDNA), which achieved novel fluorescence assay for detection of both mercury and silver ions. In this aptasensor, Hg2+ bound to thymidine (T) to form T-Hg2+-T base pairs and Ag+ specifically interacted with C-C mismatches to produce C-Ag+-C base pairs. The conformation changes prevented the aptamer from binding to its complementary sequences to form dsDNA and caused a fluorescence intensity decrease with PicoGreen. The change in the fluorescence intensity made it possible to detect both Hg2+ and Ag+ in a dose-dependent manner. The sensing system could detect as low as 5x10(-8)mol/L of Hg2+ and 9.3x10(-10)mol/L of Ag+. The fluorescent intensity changes in the system were specific for Hg2+ and Ag+, making this simple and cost-effective method extremely valuable in its future applications in monitoring Hg2+ and Ag+ pollution in environmental analysis.