Figure 3.

(a) A scheme of a colorimetric DNA biosensor for visual detection Hg²⁺ based on Exo III- driven twice cycles signal amplification strategy and AuNPs. Reprinted with permission from ref. [50]. Copyright 2019 Springer Nature. (b) A scheme of a ultrasensitive electrochemical for detection Hg²⁺ based on Exo III- assisted double cycles signal amplifi-cation strategy and gold electrodes. Reprinted with permission from ref. [51]. Copyright 2018 Royal Society of Chem-istry. (c) A scheme of a fluorescence DNA biosensor for Hg²⁺ detection based on G-quadruplex/NMM as a reporter. Reprinted with permission from ref. [52]. Copyright 2020 Elsevier. (d) A scheme of a triple signal amplification strategy for ultrasensitive Hg²⁺ detection. Reprinted with permission from ref. [54]. Copyright 2020 Royal Society of Chemistry.