Application of DNA/Ag nanocluster fluorescent probe for the detection of Pb2+

Abstract

Lead ion (Pb2+) is one of the most toxic forms of heavy metal, which may affect the environment adversely and pose severe risks to human health. Also it usually induces toxic effects in plants and animals, delays physical or mental development in children, and damages nervous, renal and immune systems. Therefore, sensitive and on-site tracking Pb2+ is highly desirable in environmental protection, as well as disease prevention and treatment. In this paper, hairpin-DNA with a poly-C loop and G-rich stem is selected as a template to synthesize DNA/Ag nanocluster: Ag+ firstly binds with C in the poly-C loop of hairpin DNA, and then is reduced by NaBH4 to form highly fluorescent hairpin DNA/Ag nanocluster. However, in the presence of Pb2+, Pb2+ induces hairpin DNA transforming into Pb2+-stabilized G-quadruplex with the structure of hairpin DNA destroyed, and the synthesized DNA/Ag nanoclusters presented a greatly decreased fluorescence. Importantly, the fluorescence changes of Ag nanoclusters in the absence and presence of Pb2+ are largely dependent on sequences of hairpin DNA and the number of complementary bases appearing in stem portion(six base pairs are optimized). Based on the difference in fluorescent intensity of DNA/Ag nanoclusters (in the absence and presence of Pb2+), Pb2+ could be quantitatively detected with the concentration ranged from 100 μmol/L to 100 nmol/L. The detection limit is 10 nmol/L. This assay is selective for Pb2+ and successfully applied to detect Pb2+ in real water sample. The result of the fluorescent assay for Pb2+ is highly consistent with that of atomic absorption spectroscopy, which presented that the fluorescent assay is reliable. As a result, a simple and sensitive fluorescent assay based on DNA/Ag nanoclusters is developed for the detection of Pb2+, which provides a potential application for Pb2+ detection in the real samples.