DNA-templated fluorescent silver nanoclusters on-off switch for specific and sensitive determination of organic mercury in seafood.

Organic mercury including methyl-mercury and ethyl-mercury (CH3Hg+ and C2H5Hg+) has high toxicity and bio-accumulation, and thus is easy to generate bio-amplification in food chain. Hence, the specific detection of organic mercury has great significance for objectively assessing the health risk of mercury in seafood. We herein designed an aptamer (AS-T7), which consists of a silver nanoclusters (AgNCs) scaffold sequence (AS) and a T-rich sequence (AT7), for simultaneously synthetizing DNA-templated AgNCs and recognizing organic mercury, and further developed a label-free fluorescent method for the sensitive and specific determination of organic mercury (CH3Hg+ and C2H5Hg+ total concentration) by using DNA-templated AgNCs as signal. Without organic mercury, Ag+ in the mixture of aptamer and Ag+ was bond on AS of aptamer to form AS-templated AgNCs after reduction, and thus emitted strong fluorescence. Whereas, in the presence of organic mercury, CH3Hg+/C2H5Hg+ was bond on AT7 of aptamer to generate photoinduced electron transfer (PET) between CH3Hg+/C2H5Hg+ and AS-templated AgNCs, and thus results in fluorescence quenching of AS-templated AgNCs. The fluorescent method could be used to rapidly detect organic mercury with a detection limit of 5.0 nM (i.e. 1.01 ng Hg/g), which meets the U.S. EPA standard of 0.3 mg/kg (wet). The method was successfully used to detect organic mercury in water and fish muscle with a recovery of 96%-104% and an inter-days RSD (n = 5) < 7%. The success of the study promised a reliable method for rapid and specific detection of organic mercury in environmental and biological samples.