Control of the Fluorescence of DNA-templated Silver Nanoclusters by Adenosine Triphosphate and Mercury(II)

Several DNA templates with the sequence 5′-T _n TAACCCCTAACCCCT-3′ (n = 0, 15, 30, and 45) were used to prepare DNA template–silver nanoclusters (DNA–Ag NCs). The T _n sequence acts as a recognition element for Hg²⁺, while the rest of the sequence acts as a template for DNA–Ag NCs. At pH 3.0, the fluorescence intensity of DNA–Ag NCs is enhanced by ATP, and the enhanced fluorescence is quenched by Hg²⁺. The length of polyT shows a slight effect on the sensitivity for the detection of Hg²⁺ but almost no effect on the optical properties of DNA–Ag NCs. The fluorescence response of DNA–Ag NCs (T₁₅-DNA–Ag NCs) vs. Hg²⁺ concentration shows two linear ranges over 10–100 and 100–1000 nM, mainly because of the fluorescence quenching due to DNA conformational changes through T–Hg²⁺–T coordination and the formation of an amalgam with Ag NCs, respectively. The sensitivity of the T₁₅-DNA–Ag NC probe was validated through the analysis of Hg²⁺ in spiked pond water. Based on the switch-on and switch-off fluorescence properties of T₁₅-DNA–Ag NCs, an IMPLICATION logic gate was fabricated using the concentrations of ATP and Hg²⁺ as inputs and the fluorescence intensity at 585 nm as output.