Dual-mode ratiometric optical sensor for rapid visual detection of Hg with poly(adenine)-assisted silver nanoclusters anchoring on tetrahedral DNA framework.

Cytosine-rich and poly(adenine)-tailed tetrahedral DNA framework (TDF) is designed as template (A-TDF) for anchoring silver nanoclusters (AgNCs) and igniting the dual-color fluorescence of AgNCs. The resultant DNA-AgNCs simultaneously emits red and green fluorescence, and the quantum yield of red fluorescence is as high as 44.8%. The red fluorescence can be selectively quenched by Hg within 2 min due to the redox reaction between Hg and Ag as well as the subsequent Ag amalgamation. Meanwhile, the green fluorescence is enhanced. Thus a ratiometric fluorescence sensor is constructed for rapid and visual Hg detection based on the synchronous change of two fluorescence signals. In addition, the resultant AgNCs probe also provides ratiometric colorimetric sensing of Hg and simultaneously shows a visible color change from pink to yellow along with increasing content of Hg. The detection limits of ratiometric fluorescence and colorimetric modes are 0.24 nM and 1.32 nM, respectively. The method has been applied to the determination of Hg in water samples, and recoveries ranged between 94.1 and 108.7%. This study not only provides a new guideline to modulate the fluorescence emission of AgNCs by scientifically designing terminal DNA sequence but also provides a facile and efficient single-probe and dual-mode ratiometric sensing platform for the routine determination and field monitoring of Hg.