Construction of a Target-Initiated, Enzyme-Free DNA Cascade Circuit for Amplified Detection of Mercury.

Here, we designed a target-initiated, enzyme-free DNA cascade circuit for highly selective and sensitive detection of Hg 2+ with dual amplification based on concatenated fuel stimulant powered (FSP) and catalytic hairpin assembly (CHA) circuits. In a typical FSP-CHA procedure, in the presence of Hg 2+ , the invading DNA activated the upstream FSP circuit to release the hidden strands containing multiple trigger units, which subsequently motivated the downstream CHA circuit to drive the cross-opening of two hairpin substrates, generating tremendously amplified fluorescence signals. A good linearity between the fluorescence intensity and Hg 2+ concentrations was observed in the range from 0.2 nM to 20 nM. The proposed system showed great applicability for sensing Hg 2+ in environmentally relevant water samples.