title: Ag+ and cysteine quantitation based on G-quadruplex-hemin DNAzymes disruption by Ag+.
abstract: Some G-quadruplex-hemin complexes are DNAzyme peroxidases that efficiently catalyze H(2)O(2)-mediated reactions, such as the oxidation of ABTS (2,2'-azinobis(3-ethylbenzothiozoline)-6-sulfonic acid) by H(2)O(2). Since Ag(+) chelates guanine bases at the binding sites are involved in G-quadruplex formation, the presence of Ag(+) may disrupt these structures and inhibit the peroxidase activity of G-quadruplex-hemin DNAzymes. On the basis of this principle, a highly sensitive and selective Ag(+)-detection method was developed. The method allows simple detection of aqueous Ag(+) with a detection limit of 64 nM and a linear range of 50-3000 nM. Cysteine (Cys) is a strong Ag(+)-binder and competes with quadruplex-forming G-rich oligonucleotides for Ag(+)-binding, promoting the reformation of G-quadruplexes and increasing their peroxidase activity. Therefore, the Ag(+)-sensing system was also developed as a Cys-sensing system. This "turn-on" process allowed the detection of Cys at concentrations as low as 50 nM using a simple colorimetric technique. The Cys-sensing system could also be used for the detection of reduced glutathione (GSH). Neither the Ag(+)-sensing nor the Cys-sensing systems required labeled oligonucleotides. In addition, both gave large changes in absorbance signal that could be observed by the naked eye. Thus, a simple visual method for Ag(+)- or Cys-detection was developed.
authors.forename: Xue-Hui
authors.initials: XH
authors.lastname: Zhou
authors.forename: De-Ming
authors.initials: DM
authors.lastname: Kong
authors.forename: Han-Xi
authors.initials: HX
authors.lastname: Shen
mesh_terms: D001665:Binding Sites; D003124:Colorimetry / Q000379:methods*; D003545:Cysteine / Q000032:analysis*; D021881:DNA, Catalytic / Q000737:chemistry* / Q000378:metabolism; D054856:G-Quadruplexes; D005978:Glutathione / Q000032:analysis / Q000737:chemistry; D006427:Hemin / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D010084:Oxidation-Reduction; D012834:Silver / Q000032:analysis* / Q000737:chemistry
chemical_list: D021881:DNA, Catalytic; D012834:Silver; D006427:Hemin; D006861:Hydrogen Peroxide; D005978:Glutathione; D003545:Cysteine