A Simple Colorimetric Assay for Sensitive Cu(2+) Detection Based on the Glutathione-Mediated Etching of MnO(2) Nanosheets

In this paper, we developed a quick, economical and sensitive colorimetric strategy for copper ions (Cu(2+)) quantification via the redox response of MnO(2) nanosheets with glutathione (GSH). This reaction consumed MnO(2) nanosheets, which acted as a catalyst for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue product (oxTMB). In the presence of Cu(2+), the GSH was catalyzed to GSSG (oxidized glutathione), and the solution changed from colorless to deep blue. Under the optimum conditions, the absorption signal of the oxidized product (oxTMB) became proportional to Cu(2+) concentration in the range from 10 to 300 nM with a detection limit of 6.9 nM. This detection system showed high specificity for Cu(2+). Moreover, the system has been efficaciously implemented for Cu(2+) detection in actual tap water samples. The layered-nanostructures of MnO(2) nanosheets make it possess high chemical and thermal stability. TMB can be quickly oxidized within 10 min by the catalyzing of MnO(2) nanosheets with high oxidase-like activity. There is no need of expensive reagents, additional H(2)O(2) and complicated modification processes during the colorimetric assay. Therefore, the strategy primarily based on MnO(2) nanosheets is promising for real-time, rapid and highly sensitive detection of Cu(2+) under practical conditions.