Use of fluorescent DNA-templated gold/silver nanoclusters for the detection of sulfide ions

We have developed a one-pot approach to prepare fluorescent DNA-templated gold/silver nanoclusters (DNA-Au/Ag NCs) from Au ³⁺, Ag ⁺, and DNA (5′-CCCTTAATCCCC-3′) in the presence of NaBH ₄ in order to detect sulfide (S ^2-) ions on the basis of fluorescence quenching. The as-prepared DNA-Au/Ag NCs have been characterized by UV-vis absorption, fluorescence, circular dichroism, X-ray photoelectron spectroscopy, and electrospray ionization-mass spectrometry measurements. Relative to DNA-Ag NCs, DNA-Au/Ag NCs are much more stable in high ionic strength media (e.g., 200 mM NaCl). The quantum yield of the as-prepared DNA-Au/Ag NCs is 4.5%. We have demonstrated that the fluorescence of DNA-Au/Ag NCs is quenched by S ^2- ions through the interaction between sulfide ions and gold/silver atoms/ions, a result which leads to changes in the conformation of the templated DNA from packed hairpin to random coil structures. These changes in fluorescence intensity allow sensitive detection of S ^2- ions at concentrations as low as 0.83 nM. To minimize interference from I ^- ions for the detection of S ^2- ions using the DNA-Au/Ag NCs, the addition of sodium peroxydisulfate to the solution is essential. We have validated the practicality of this probe for the detection of S ^2- ions in hot spring and seawater samples, demonstrating its advantages of simplicity, sensitivity, selectivity, and low cost.