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

Nanozymes based on manganese oxide (MnO) are demonstrated to be promising probes in colorimetric sensing applications. In this study, the r-MnO/β-MnO 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-MnO/β-MnO exhibits a remarkably good catalytic activity in the oxidation process of 3,3',5,5'-tetramethylbenzidine (TMB) compared with the r-MnO or MnO nanostructure owing to its heterophase junctions. The enhanced performance of the colorimetric sensor for ascorbic acid (AA) detection was investigated using the r-MnO/β-MnO heterophase nanostructure as probe. The r-MnO/β-MnO 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 MnO-based colorimetric sensor and their practical application in plant growth monitoring.