Direct visual detection of MnO2 nanosheets within seconds.

Abstract

The increasing application of nanomaterials will inevitably lead to their release into the environment, which may pose a threat to the environment and human health. As such, there is an urgent need to detect various nanomaterials. In the present work, we present a novel, rapid, and simple visual detection of MnO2 nanosheets in buffer solution and environmental water sample. In this assay, a redox reaction between MnO2 nanosheets and 3,3',5,5'-tetramethylbenzidine (TMB) occurred, leading to the oxidation of TMB to TMB diimine. This redox reaction generated different colors dependent on the concentration of MnO2 nanosheets, including colorless, blue, green, and yellow, which allowed semiquantitative detection of MnO2 nanosheets with the naked eye. The detection range of the visual assay was 2-15 μg/mL, and the minimum concentration of MnO2 nanosheets can be visually detected at concentrations down to 2.0 μg/mL. Moreover, the developed visual assay showed a high selectivity to MnO2 nanosheets over Mn(2+) ions, tetramethylammonium hydroxide, hydrogen peroxide, graphene oxide, and graphitic carbon nitride nanosheets.