Au/MnO ₂ featuring efficient oxidase-mimic activity at neutral pH: toward a portable dual-modal sensor for sulfide detection integrated with a smartphone

The rapid detection of sulfide compounds including glutathione (GSH) and S₂O₈^2- is of great interest because they play essential roles in the process of food processing. Here, we design a colorimetric/smartphone dual-mode sensing platform to simultaneously detect GSH and S₂O₈^2- using gold nanoparticle-decorated MnO₂ nanosheets (Au/MnO₂ NSs). Because of its distinct structure, Au/MnO₂ possesses superior catalytic activity similar to native oxidase capable of catalysing the direct oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) under near-neutral pH conditions. Meanwhile, this catalytic reaction results in an obvious color change in the solution, which senses GSH and S₂O₈^2- through redox and diazotization reactions. The designed sensor enables the value-assisted and visual determination of GSH and S₂O₈^2- with a limit of detection of 2.3 nM. Based on the dual-mode sensing system, a smartphone-mediated "all-in-one" sensing platform is designed to realize the real-time and intelligent monitoring of GSH and S₂O₈^2-. This work provides a new avenue to construct multifunctional sensors to achieve the visualization and portable determination of sulfide compounds.