Specifically and Visually Detect Methyl-Mercury and Ethyl-Mercury in Fish Sample Based on DNA-Templated Alloy Ag-Au Nanoparticles.

Methyl-mercury (CH3Hg+) and ethyl-mercury (C2H5Hg+) have much higher toxicity than Hg2+ and can be more easily accumulated by organisms to form severe bioamplification. Hence, the specific and on-site detection of CH3Hg+ and C2H5Hg+ in seafood is of great significance and a hard challenge. We herein designed two T-rich aptamers (HT5 and HT7) for specifically recognizing CH3Hg+ and the total of CH3Hg+ and C2H5Hg+, respectively. In the presence of all Au3+, Ag+, and T-rich aptamer, CH3Hg+ and C2H5Hg+ specifically and preferentially bind with aptamer and thus induced the formation of alloy Ag-Au nanoparticles after reduction, which led to the color change in solution. This provided a sensing platform for the instrument-free visual discrimination and detection of CH3Hg+ and C2H5Hg+. By using HT5 as probe, the method can be used to detect as low as 5.0 μM (equivalent to 1.0 μg Hg/g) of CH3Hg+ by bare eye observation and 0.5 μM (equivalent to 100 ng Hg/g) of CH3Hg+ by UV-visible spectrometry. By using HT7 as probe, the method can be used to detect the total concentration of CH3Hg+ and C2H5Hg+ with a visual detection limit of 5.0 μM (equivalent to 1.0 μg Hg/g) and a UV-visible spectrometry detection limit of 0.6 μM (equivalent to 120 ng Hg/g). The proposed method has been successfully used to detect CH3Hg+ and C2H5Hg+ in fish muscle samples with a recovery of 101-109% and a RSD ( n = 6) < 8%. The success of this study provided a potential method for the specific and on-site detection of CH3Hg+ and C2H5Hg+ in seafood by only bare eye observation.