Colorimetric sensing of silver ions based on glutathione-mediated MnO2 nanosheets

- A simple, rapid colorimetric platform has been proposed for detection of Ag+ by naked eyes.
- The glutathione-mediated MnO2 nanosheets can catalyze colorless TMB into blue oxTMB instantaneously.
- The limit of detection is 4.23 nM, which is of sensitivity to existing other methods.
- The proposed colorimetric sensor is of high sensitive and selectivity in water and practical samples.

We described a rapid and highly sensitive colorimetric method for the detection and quantification of silver ions employing glutathione (GSH)-mediated MnO2 nanosheets as an artificial oxidase. In this assay,the absorption intensity of the chromogenic reaction system enabled the quantification of silver ions. Under the optimum conditions, the linear response ranged for Ag+ was from 10 nM to 800 nM with a correlation coefficient of 0.996. Remarkably, limit of detection in aqueous solutions was 4.23 nM, which was well below United States Environmental Protection Agency (USEPA) permissible limit in drinking water (460 nM). This sensing assay had highly specificity because no significant interference occurred with 10-fold concentration of other metal ions. Moreover, the approach also could be employed to the Ag+ detection in real samples. And the recovery of Ag+ spiked in tap water ranged from 99.62% to 108.01%. Importantly, the oxidation reaction of TMB to oxTMB by MnO2 nanosheets completed instantaneously even by naked-eye readout. Therefore, the assay based on GSH-mediated MnO2 nanosheets is simple, rapid, highly sensitive and selective for the quantification of Ag+ in water and practical samples.