Selenium Hydride-Induced Oxidase-like Activity Inhibition of Amorphous/Crystalline Manganese Dioxide: Colorimetric Assay for Selenium Detection

Hydride generation-based optical sensors have achieved on-site visual selenium (Se) determination with high anti-interference capability, yet they rely on the change of single-color intensity with a narrow linear dynamic range. Herein, we combined selenium hydride (H2Se)-induced activity inhibition of a manganese dioxide (MnO2) nanozyme with different degrees of 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation to realize sensitive multicolor visual detection of Se(IV). Due to its high oxidase-like (OXD-like) activity and sensitive response to H2Se, amorphous/crystalline manganese dioxide (ac-MnO2) was selected to form the headspace single droplet for microextraction and recognition. Via headspace redox reaction with H2Se, ac-MnO2 was reduced into low valence accompanied by in situ generation of Se nanoparticles, leading to the formation of a Se-MnOx aggregate. The experimental results and theoretical calculation indicated that, compared with MnO2, Se-MnOx had decreased active sites for adsorbing O2 to generate •O2–, resulting in the nanozyme activity inhibition that was totally dependent on Se(IV) concentration. The implementation of this strategy enabled accurate Se(IV) detection with a linear range from 10 to 600 μg L–1 and a limit of detection of 1.8 μg L–1. The portable smartphone-based detection for real sample analysis further demonstrated that this assay can be an easy, convenient, and intelligent tool for on-site selenium determination.