Target-mediated base-mismatch initiation of a non-enzymatic signal amplification network for highly sensitive sensing...

Because of its adverse environmental effects, the establishment of convenient methods for monitoring Hg2+ with ultrahigh sensitivity is important to human health. With a new target-mediated base-mismatch initiation of a signal amplification network strategy, we describe the development of a simple fluorescence sensing approach for detecting Hg2+ in water samples with high sensitivity. The assistant DNA probes trigger the catalytic hairpin assembly (CHA) of two elaborately designed hairpins for the formation of many Mg2+-dependent DNAzymes via T-Hg2+-T base mismatch hybridization. Subsequently, the fluorescence-quenched signal probes are cyclically cleaved by these DNAzymes to recover fluorescence and to release lots of secondary target sequences, which synchronously trigger the CHA of the two hairpins to form a signal amplification network to yield drastically enhanced fluorescence for detecting Hg2+ with high sensitivity at 7.9 pM. Moreover, two mismatched bases are incorporated into the hairpin probes to reduce the background noise to further enhance sensitivity. The developed sensing method exhibits excellent selectivity toward Hg2+ and works well for real water samples. The successful implementation of our amplification strategy for the detection of Hg2+ can make this sensing method a non-enzymatic and convenient signal amplification means for detecting other biomolecules.