DNA/Single-Walled Carbon Nanotubes Based Fluorescence Detection of Hg2+

A new, highly selective, and sensitive technique has been developed for the detection of Hg²⁺ using singled-wall carbon nanotubes (SWNTs) and two kinds of oligonucleotides. The fluorescence of the thymine-rich single stranded DNA labeled with dye (the probe ssDNA) was effectively quenched by the SWNTs. In the presence of a target DNA (rich T-T mismatched with probe), the tightness of the DNA wrapping around the SWNTs was loosened. Since binding of Hg²⁺ turned the T-T mismatches to stable T-Hg²⁺-T base pairs, and the binding rate of DNA and the nanotube was lower than that of DNA hybridization, it induced the release of DNA molecules from the SWNTs, and this resulted in a remarkable increase of fluorescence compared to that of the DNA-SWNTs. The assay exhibited a dynamic response range for Hg²⁺ from 4.52 × 10^?8 M to 7.21 × 10^?7 M with a detection limit of 10 nM.