MnO nanoparticles decorated porous reduced graphene oxide with excellent oxidase-like activity for fast colorimetric detection of ascorbic acid.

MnO nanoparticles composed of porous reduced graphene oxide nanosheets (MnO@p-rGO) with enhanced oxidase-like activity were successfully fabricated through an in-situ approach for fast colorimetric detection of ascorbic acid (AA). The residual Mn in the GO suspension of Hummers method was directly reused as the manganese source, improving the atom utilization efficiency. Benefiting from the uniform distribution of MnO nanoparticles on the surface of p-rGO nanosheets, the nanocomposite exhibited larger surface area, more active sites, and accelerated electron transfer efficiency, which enhanced the oxidase-like activity. MnO@p-rGO nanocomposite efficiently activate dissolved O to generate singlet oxygen (O), leading to high oxidation capacity toward the substrate 3,3',5,5'-tetramethylbenzidine (TMB) without the extra addition of HO. Furthermore, the prominent absorption peak of the blue ox-TMB at 652 nm gradually decreased in the presence of AA, and a facile and fast colorimetric sensor was constructed with a good linear relationship (0.5-80 μM) and low LOD (0.278 μM) toward AA. Owing to the simplicity and excellent stability of the sensing platform, its practical application for AA detection in juices has shown good feasibility and reliability compared with HPLC and the 2, 4-dinitrophenylhydrazine colorimetric method. The oxidase-like MnO@p-rGO provides a versatile platform for applications in food testing and disease diagnosis.