Gold Nanoparticle-Based Colorimetric and “Turn-On” Fluorescent Probe for Mercury(II) Ions in Aqueous Solution

Abstract

An approach for visual and fluorescent sensing of Hg2+ in aqueous solution is presented. This method is based on the Hg(2+)-induced conformational change of a thymine (T)-rich single-stranded DNA (ssDNA) and the difference in electrostatic affinity between ssDNA and double-stranded (dsDNA) with gold nanoparticles. The dye-tagged ssDNA containing T-T mismatched sequences was chosen as Hg2+ acceptor. At high ionic strength, introduction of the ssDNA to a colloidal solution of the aggregates of gold nanoparticles results in color change, from blue-gray to red of the solution, and the fluorescence quenching of the dye. Binding of Hg2+ with the ssDNA forms the double-stranded structure. This formation of dsDNA reduces the capability to stabilize bare nanoparticles against salt-induced aggregation, remaining a blue-gray in the color of the solution, but fluorescence signal enhancement compared with that without Hg2+. With the optimum conditions described, the system exhibits a dynamic response range for Hg2+ from 9.6 x 10(-8) to 6.4 x 10(-6) M with a detection limit of 4.0 x 10(-8) M. Both the color and fluorescence changes of the system are extremely specific for Hg2+ even in the presence of high concentrations of other heavy and transition metal ions, which meet the selective requirements for biomedical and environmental application. The combined data from transmission electron microscopy, fluorescence anisotropy measurements, and dialysis experiments indicate that both the color and the fluorescence emission changes of the DNA-functioned gold nanoparticles generated by Hg2+ are the results of the metal-induced formation of dsDNA and subsequent formation of nanoparticle aggregates.

A highly selective and sensitive colorimetric sensor for iodide detection based on anti-aggregation of gold nanoparticles

“…4a and b). To obtain a better performance, we chose the pH at 7.4, avoiding the protonation of the nitrogen atoms of the thymine at lower pH or the interference of OH − induced by higher solution pH [40,41]. In all subsequent experiments, we used 20 mM PBS buffer solution to keep the pH value at 7.4.…”

Novel Hg2+-imprinted polymers based on thymine–Hg2+–thymine interaction for highly selective preconcentration of Hg2+ in water samples

“…2). The influence of pH on T-Hg 2+ -T interaction has been reported as following: at a pH below 7.0, protonation of the nitrogen atoms of the T base reduces its affinity with Hg 2+ , while at a relatively higher pH (>10.0), Hg 2+ may be complexed by OH − , which in turn, may reduce its complex with the T [35]. The binding affinity of T with Hg 2+ had significant effect on the binding capacity of IIPs-T. Higher binding affinity of T-Hg 2+ -T resulted in higher binding capacity of IIPs-T.…”

Immobilization of DNA on Magnetic Microparticles for Mercury Enrichment and Detection with Flow Cytometry

“…[18] While thymine binding to mercury has been known for a long time, [19,20] this study was the first attempt to use a thymine-rich DNA for mercury detection. Since then, this DNA-based mercury recognition mechanism has been used to design many fluorescent, [16,17,[21][22][23][24][25] colorimetric, [11,[26][27][28][29][30][31][32][33][34][35] and electrochemical sensors. [36] Currently, detection limits in the low nanomolar range can be reached.…”