The Triple Roles of Glutathione for a DNA-Cleaving DNAzyme and Development of a Fluorescent Glutathione/Cu(2+)-Dependent DNAzyme Sensor for Detection of Cu(2+) in Drinking Water.

Pistol-like DNAzyme (PLDz) is an oxidative DNA-cleaving catalytic DNA with ascorbic acid as cofactor. Herein, glutathione was induced into the reaction system to maintain reduced ascorbic acid levels for higher efficient cleavage. However, data indicated that glutathione played triple roles in PLDz-catalyzed reactions. Glutathione alone had no effect on PLDz, and showed inhibitory effect on ascorbic acid-induced PLDz catalysis, but exhibited stimulating effect on Cu(2+)-promoted self-cleavage of PLDz. Further analysis of the effect of glutathione/Cu(2+) on PLDz indicated that H2O2 played a key role in PLDz catalysis. Finally, we developed a fluorescent Cu(2+) sensor (PL-Cu 1.0) based on the relationship between glutathione/Cu(2+) and catalytic activity of PLDz. The fluorescent intensity showed a linear response toward the logarithm concentration of Cu(2+) over the range from 80 nM to 30 μM, with a detection limit of 21.1 nM. PL-Cu 1.0 provided only detection of Cu(2+) over other divalent metal ions. Ca(2+) and Mg(2+) could not interfere with Cu(2+) detection even at a 1000-fold concentration. We further applied PL-Cu 1.0 for Cu(2+) detection in tap and bottled water. Water stored in copper taps overnight had relatively high Cu(2+) concentrations, with a maximum 22.3 μM. Trace Cu(2+) (52.2 nM) in deep spring was detected among the tested bottled water. Therefore, PL-Cu 1.0 is feasible to detect Cu(2+) in drinking water, with a practical application.