Multicolor Aptasensor Based on DNA-Induced Au-Ag Nanorods for Simultaneous and Visual Detection of Inorganic and Organic Mercury

Compared to inorganic mercury (Hg2+), methyl-mercury (CH3Hg+) and ethyl-mercury (C2H5Hg+) (organic mercury) not only have a much stronger toxicity but also are more easily accumulated by marine organisms to produce bioamplification. Therefore, the simultaneously onsite detection of Hg2+ and organic mercury is of great significance to ensure the safety of seafood, and it is also a hard challenge. We designed a T-rich aptamer, H-T7, for specifically recognizing Hg2+ and organic mercury and developed a multicolor aptasensor for simultaneous discrimination and detection of Hg2+ and organic mercury with only bare-eye observation using H-T7 as a recognition probe and gold nanorods (AuNRs) as a signal. In the presence of Hg2+ and Ag+, Hg2+ preferentially and specifically bind with H-T7 immobilized on AuNRs surface and induce the formation of a monolayer Ag/Hg amalgam on the AuNRs surface after reduction, resulting in a change in color from orange to faint purple and a corresponding shift in the absorption peak from 820 to 730 nm in the solution. However, in the presence of CH3Hg+ or C2H5Hg+ and Ag+, CH3Hg+ or C2H5Hg+ preferentially bind with H-T7 immobilized on the AuNRs surface and induce the formation of a monolayer Ag-0 on the AuNRs surface after reduction, which results in the change in color from orange to atrovirens and the corresponding shift in the absorption peak shift from 820 to 670 nm in the solution. Thus, the inorganic and organic mercury (total of CH(3)Hg(+ )and C2H5Hg+) can be specifically discriminated and detected by only bare-eye observation. The method can be used to simultaneously detect inorganic and organic mercury in seawater by the bare-eye observation with a visual detection limit of 2.0 ppm for Hg2+ and 10.0 ppm for organic mercury. The success of this study is a useful enlightenment to develop an instrument-free method for an onsite detection of trace inorganic and organic mercury in environment by a bare-eye observation, although the sensitivity of the method is relatively low.