title: Label-free detection of Cu(2+) and Hg(2+) ions using reconstructed Cu(2+)-specific DNAzyme and G-quadruplex DNAzyme.
abstract: Label-free metal ion detection methods were developed. To achieve these, a reconstructed Cu(2+)-specific DNA-cleaving DNAzyme (Cu(2+)-specific DNAzyme) with an intramolecular stem-loop structure was used. G-quadruplex-forming G-rich sequence(s), linked at the ends of double-helix stem of an intramolecular stem-loop structure, was partly caged in an intramolecular duplex or formed a split G-quadruplex. Cu(2+)-triggered DNA cleavage at a specific site decreased the stability of the double-helix stem, resulting in the formation or destruction of G-quadruplex DNAzyme that can effectively catalyze the 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS)-H2O2 reaction. Based on these, two label-free, cost-effective and simple Cu(2+) sensors were designed. These two sensors followed different detection modes: 'turn-on' and 'turn-off'. As for the 'turn-on' sensor, the intramolecular stem-loop structure ensured a low background signal, and the co-amplification of detection signal by dual DNAzymes (Cu(2+)-specific DNAzyme and G-quadruplex DNAzyme) provided a high sensitivity. This sensor enabled the selective detection of aqueous Cu(2+) with a detection limit of 3.9 nM. Visual detection was possible. Although the 'turn-off' sensor gave lower detection sensitivity than the 'turn-on' one, the characteristics of cost-effectiveness and ease of operation made it an important implement to reduce the possibility of pseudo-positive or pseudo-negative results. Combining the ability of Hg(2+) ion to stabilize T-T base mismatch, above dual DNAzymes-based strategy was further used for Hg(2+) sensor design. The proposed sensor allowed the specific detection of Hg(2+) ion with a detection of 4.8 nM. Visual detection was also possible.
authors.affiliation: State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin, P. R. China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Xiao-Xi
authors.initials: XX
authors.lastname: Huang
authors.forename: Yang
authors.initials: Y
authors.lastname: Cai
authors.forename: Hao-Jie
authors.initials: HJ
authors.lastname: Xiao
authors.forename: Qiu-Fen
authors.initials: QF
authors.lastname: Zhang
authors.forename: De-Ming
authors.initials: DM
authors.lastname: Kong
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D003124:Colorimetry / Q000379:methods; D003300:Copper / Q000737:chemistry*; D021881:DNA, Catalytic / Q000737:chemistry*; D054856:G-Quadruplexes; D008628:Mercury / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet; D013194:Staining and Labeling
chemical_list: D021881:DNA, Catalytic; D003300:Copper; D008628:Mercury
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