Ag+ and Cysteine Quantitation Based on G-Quadruplex−Hemin DNAzymes Disruption by Ag+

摘要

Some G-quadruplex-hemin complexes are DNAzymenperoxidases that efficiently catalyze H2O2-mediated reactions,nsuch as the oxidation of ABTS (2,2′-azinobis(3-nethylbenzothiozoline)-6-sulfonic acid) by H2O2. SincenAg+ chelates guanine bases at the binding sites areninvolved in G-quadruplex formation, the presence ofnAg+ may disrupt these structures and inhibit thenperoxidase activity of G-quadruplex-hemin DNAzymes.nOn the basis of this principle, a highly sensitive andnselective Ag+-detection method was developed. Thenmethod allows simple detection of aqueous Ag+ with andetection limit of 64 nM and a linear range of 50-3000nnM. Cysteine (Cys) is a strong Ag+-binder and competesnwith quadruplex-forming G-rich oligonucleotidesnfor Ag+-binding, promoting the reformation of Gquadruplexesnand increasing their peroxidase activity.nTherefore, the Ag+-sensing system was also developednas a Cys-sensing system. This “turn-on” process allowednthe detection of Cys at concentrations as low asn50 nM using a simple colorimetric technique. The Cyssensingnsystem could also be used for the detection ofnreduced glutathione (GSH). Neither the Ag+-sensingnnor the Cys-sensing systems required labeled oligonucleotides.nIn addition, both gave large changes innabsorbance signal that could be observed by the nakedneye. Thus, a simple visual method for Ag+- or Cysdetectionnwas developed.