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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 Pb2+ or Hg2+ in water. In the presence of Hg2+, the Hg2+ was fixed to the aptamer chain by thymine-Hg2+-thymine (T-Hg2+-T), resulting in the decrease of signal. When Pb2+ was present, DNA single strand S2 dissociated and was bound to Pb2+, 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, Pb2+ or Hg2+, and the detection limits were 17.0 pg/L (R2 = 0.993) and 12.0 pg/L (R2 = 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. [ABSTRACT FROM AUTHOR]

MXene@Au as the base and Au@SiO2 as signal amplification factor were used for constructing an ultrasensitive "on–off" electrochemiluminescence (ECL) biosensor for the detection of Pb2+ in water. The use of MXene@Au composite provided a good interface environment for the loading of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)32+) on the electrode. Based on resonance energy transfer, the Au (core) SiO2 (shell) (Au@SiO2) nanoparticles stimulate electron transport and promote tripropylamine (TPrA) oxidation. The luminescence effect of Au@SiO2 was five times that of AuNPs and SiO2 nanomaterials alone, and the ECL intensity was greatly improved. In addition, Pb2+ activated the aptamer to exert its endonuclease activity, which realized the signal cycle amplification in the process of Pb2+ detection. When Pb2+ was added, the ECL signal weakened, and the Pb2+ concentration was detected according to the decreased ECL intensity. Under optimized experimental conditions, this aptamer sensor for Pb2+ has a wide detection range (0.1 to 1 × 106 ng L−1) and a low detection limit (0.059 ng L−1). The relative standard deviation (RSD) of the sensor is 0.39–0.99%, and the recovery of spiked standard is between 90.00 and 125.70%. The sensor shows good selectivity and high sensitivity in actual water sample analysis. This signal amplification strategy possibly provides a new method for the detection of other heavy metal ions and small molecules. [ABSTRACT FROM AUTHOR]