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 bioaccumulation, 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.

Automated summary

A novel aptamer for detecting organic mercury was designed, and a label-free fluorescent method for sensitive and specific determination of organic mercury total concentration was developed. The method showed rapid, accurate, and reliable characteristics, making it suitable for detecting organic mercury in environmental and biological samples.