Single-labeled hairpin probe for highly specific and sensitive detection of lead(II) based on the fluorescence quenching of deoxyguanosine and G-quartet

Specific and homogeneous detection of heavy metal ion is of great importance for both human health care and environmental protection. We reported a highly specific and sensitive assay for fluorescent detection of Pb2+ based on the difference in quenching ability between deoxyguanosines and G-quartet by using carboxyfluorescein-labeled hairpin DNA (F-hpDNA) as a recognition probe. In the absence of target, the fluorescence of F-hpDNA can be quenched through photoinduced electron transfer from the dye to deoxyguanosines because the formation of hairpin brings deoxyguanosines close to the FAM. In the presence of Pb2+, the formation of G-quadruplex DNA leads to a significant decrease in fluorescence due to the effective stack of dye on the G-quartet, which obviously intensified the quenching of fluorophore. In comparison with linear DNA probe, hairpin DNA probe greatly improved the specificity, and Pb2+ can be highly selective detected even when coexisted with other metal ions. The quenching efficiency is linear with the concentration of lead(II) over the range of 0.5-500 nM, with a limit of detection of 0.4 nM. Conformational switch from hairpin to G-quadruplex was verified by CD measurements. Moreover, the application for detection of real samples further demonstrated its reliability. Therefore, it is a selective, simple and sensitive approach for detection of lead ion, as such, it promises to provide a solid foundation for developing universal analytical method for heavy metal ions.