Colorimetric detection of mercury ions using MnO2 nanorods as enzyme mimics

Abstract

In this study, a simple and novel “off–on” colorimetric sensor for the detection of mercury ions (Hg²⁺) in aqueous solution was developed. The homogeneous MnO₂ nanorods as oxidase-like mimetics could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) into a blue colored cation radical without the requirement for additional oxidizing agents. Glutathione (GSH) could successfully hinder the cation radical production and restore them to colourless TMB molecules. Hg²⁺ had a strong affinity to thiolated compounds. If GSH and Hg²⁺ were pre-incubated, the solution would be recovered to blue colored solution in the presence of MnO₂ nanorods. Based on this phenomenon, a simple and rapid colorimetric path for the sensing of Hg²⁺ was developed. A good linear relationship could be obtained from 0.1 to 8.0 µM. The limit of detection was estimated to be 0.08 µM. The proposed method was successfully applied for the determination of Hg²⁺ in real water samples with recoveries ranging from 82% to 114%. And this method was allowed for the monitoring of Hg²⁺ directly by the naked eye.