Unveiling the role of heterophase nanostructure in MnO₂-based colorimetric sensors for ascorbic acid detection

Nanozymes based on manganese oxide (MnO₂) are demonstrated to be promising probes in colorimetric sensing applications. In this study, the r-MnO₂/β-MnO₂ heterophase nanostructure was simply prepared by a calcination process with controllable temperature. The characterization of the nanostructured material was confirmed by SEM, UV–vis spectroscopy, Raman, TGA–DSC, and XRD analysis. The r-MnO₂/β-MnO₂ exhibits a remarkably good catalytic activity in the oxidation process of 3,3′,5,5′-tetramethylbenzidine (TMB) compared with the r-MnO₂ or Mn₂O₃ nanostructure owing to its heterophase junctions. The enhanced performance of the colorimetric sensor for ascorbic acid (AA) detection was investigated using the r-MnO₂/β-MnO₂ heterophase nanostructure as probe. The r-MnO₂/β-MnO₂ material enhanced the monitoring of AA in the wide linear range from 1 µM to 50 μM with a limit of detection of 0.84 µM. This work presents a promising and straightforward approach for the construction of MnO₂-based colorimetric sensor and their practical application in plant growth monitoring.