Dual-target electrochemical DNA sensor for detection of Pb2+ and Hg2+ simultaneously by exonuclease I–assisted recycling signal amplification

With the development of exonuclease, the exonuclease has been used to construct a variety of aptasensor and to realize the signal amplification. Among them, based on silver nanoparticles (Ag NPs) and exonuclease I (Exo I)-assisted cycle signal amplification strategy, we designed a novel high-sensitivity dual-target electrochemical biosensor to detect Pb 2+ or Hg 2+ in water. In the presence of Hg 2+ , the Hg 2+  was fixed to the aptamer chain by thymine-Hg 2+ -thymine (T-Hg 2+ -T), resulting in the decrease of signal. When Pb 2+ was present, DNA single strand S2 dissociated and was bound to Pb 2+ , which automatically triggered Exo I to selectively cut the single chain from the recognition site to achieve the cyclic amplification of the electrochemical signal. The interaction between aptamer and Exo I was investigated by gel electrophoresis. Under the optimum conditions in the scan range -0.20 to 0.60 V, the biosensor had high sensitivity with a linear range of 100 pg/L to 10.0 mg/L, Pb 2+ or Hg 2+ , and the detection limits were 17.0 pg/L ( R 2  = 0.993) and 12.0 pg/L ( R 2  = 0.993), respectively. The relative standard deviation (RSD) of the sensor was 0.5–2.6%, and the recovery of spiked standard solutions was between 98.3 and 110%. The cycle amplification strategy supported by this enzyme has promising applications in detection of the two metal ions in various fields. Graphical Abstract