Ultra-sensitive “turn-on” detection method for Hg2+ based on mispairing biosensor and emulsion PCR

• Hg2+ detection system was revealed based on mispairing biosensor and emulsion PCR.
• It had a wide dynamic range from 40 pmol to 40 fmol over 4 logarithms.
• LOQ and LOD were set up as 40 and 10 fmol that could meet all detection demands.

Sensor-based detection methods have inspired the idea that chemical or physical signals could be converted to nucleic acid signals to be quantitatively detected using a combination of appropriate detection tools. To achieve ultra-sensitive and absolute quantitative detection of mercury ion (Hg2+), we have combined a mispairing biosensor for Hg2+ and emulsion PCR. The parameters that might influence the biosensor step, such as the duration of isothermal amplification and the concentration of the sensor oligonucleotide, have been firstly optimized in our study to achieve the most efficient biosensor detection. The evaluation results of secondary structures between the biosensors with different number of T-Hg-T structures achieved by Circular Dichroism have indicated that the secondary hairpin structure would be varied according to the change of number of T-Hg-T structures, which could influence the quantitative detection results. Further optimization of number of T-Hg-T within the biosensor sequences showed that 5 T-Hg-T structures could generate the most efficient amplification. After the above optimizations, the emulsion PCR has been employed to achieve the absolute quantitation of nucleic acid signals. The final results have shown that the limit of quantitation (LOQ) in our study was as low as 40 fmol, and the limit of detection (LOD) was 10 fmol. The practical detection tests showed that the quantitative results were stable and accurate for all substrates. In conclusion, by combining a mispairing biosensor with emulsion PCR, we developed a flexible and stable quantitative “turn-on” detection method with ultra-sensitivity that can detect trace amounts Hg2+ within different substrates.

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