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-MnO_x aggregate. The experimental results and theoretical calculation indicated that, compared with MnO₂, Se-MnO_x 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.