Dual-mode ratiometric fluorescent and colorimetric sensor for rapid visual detection of Hg²⁺ using poly(T)-tailed...

Rapid, sensitive, and accurate detection of heavy metal ions is significant for human health and ecological security. Herein, a novel single-stranded DNA with poly(thymidine) tail is tactfully designed as template to synthesize dual-emission silver nanoclusters (ssDNA-AgNCs). The obtained AgNCs simultaneously emit red and green fluorescence, and the red emission can be selectively quenched by Hg²⁺, meanwhile the green emission of AgNCs increases synchronously. Thus ssDNA-AgNCs as a single probe shows excellent ratiometric fluorescence sensing for Hg²⁺ with a detection limit of 0.2 nM, and Hg²⁺ as low as 10.0 nM can be fluorescently identified by naked eye within 5 min. Moreover, the proposed nanoprobe also exhibits a good ratiometric colorimetric sensing for Hg²⁺, and the obvious color change of nanoprobe also enables a rapid and visual monitoring of Hg²⁺ under visible light. The dual mode ratiometric response of Hg²⁺ can be ascribed to the rapid redox reaction between Hg²⁺ and Ag⁰ on the surface of AgNCs and the subsequent formation of silver amalgam. The resultant dual-mode ratiometric sensor has been successfully applied to the determination of Hg²⁺ in environmental water samples. This study provides a new strategy to synthesize dual-emission AgNCs by scientifically designing terminus sequence of ssDNA template, and develops a facile and efficient single-probe and dual-mode ratiometric sensor for visual monitoring of Hg²⁺.