Construction of DNA Biosensors for Mercury (II) Ion Detection Based on Enzyme-Driven Signal Amplification Strategy

Mercury ion (Hg²⁺) is a well-known toxic heavy metal ion. It is harmful for human health even at low concentrations in the environment. Therefore, it is very important to measure the level of Hg²⁺. Many methods, reviewed in several papers, have been established on DNA biosensors for detecting Hg²⁺. However, few reviews on the strategy of enzyme-driven signal amplification have been reported. In this paper, we reviewed this topic by dividing the enzymes into nucleases and DNAzymes according to their chemical nature. Initially, we introduce the nucleases including Exo III, Exo I, Nickase, DSN, and DNase I. In this section, the Exo III-driven signal amplification strategy was described in detail. Because Hg²⁺ can help ssDNA fold into dsDNA by T-Hg-T, and the substrate of Exo III is dsDNA, Exo III can be used to design Hg²⁺ biosensor very flexibly. Then, the DNAzyme-assisted signal amplification strategies were reviewed in three categories, including UO₂²⁺-specific DNAzymes, Cu²⁺-specific DNAzymes and Mg²⁺-specific DNAzymes. In this section, the Mg²⁺-specific DNAzyme was introduced in detail, because this DNAzyme has highly catalytic activity, and Mg²⁺ is very common ion which is not harmful to the environment. Finally, the challenges and future perspectives were discussed.