A T–Hg2+–T metallo-base pair-mediated dual amplification fluorescent strategy for the selective and sensitive detection of Hg2+

Abstract

The mercuric ion is a highly toxic contaminant and causes severe harm to the environment and human health. Herein, a T–Hg²⁺–T metallo-base pair-mediated dual amplification fluorescent strategy was proposed for the selective and sensitive detection of Hg²⁺ based on a target cycle and DNAzyme cycle. First, Hg²⁺ selectively bound with T–T mismatches in H-DNA and A-DNA to form stable T–Hg²⁺–T metallo-base pairs. This initiated the strand displacement between H-DNA and A-DNA to obtain the Hg²⁺-mediated partial double-stranded structure, with a blunt 3′-terminus of the opened H-DNA (donated as the Hg-complex). Next, under the action of Exo III, the Hg-complex was digested to release DNAzyme, A-DNA and Hg²⁺. The released Hg²⁺ could bind with another A-DNA and H-DNA, and the target cycle started anew, eventually generating numerous DNAzymes. DNAzymes then catalyzed the cleavage of a molecular beacon (MB) to generate free fluorophores. Upon cleavage, DNAzymes were released and continuously hybridized with another MB to trigger a second DNAzyme cycle. Finally, numerous fluorophores were liberated, resulting in a significantly amplified signal. The strategy showed a good linear relationship in the range from 2.0 × 10⁻¹⁰ mol L⁻¹ to 1.0 × 10⁻⁸ mol L⁻¹, with a detection limit of 7.2 × 10⁻¹¹ mol L⁻¹. The proposed strategy exhibited remarkable selectivity towards Hg²⁺ against other metal ions. Furthermore, this strategy was successfully applied to detect Hg²⁺ in real water samples. The proposed strategy provided a reliably quantitative candidate for potential application in environmental monitoring and biotoxicity analysis.