Electron-regulated WO3/Mn3O4 bi-enzyme activity for colorimetric detection epinephrine with smartphones

Herein, based on the excellent redox ability of the transition metal oxide Mn3O4, the key strategy of introducing WO3 was used to effectively modulate the electronic structure of the Mn active species and improve the catalyst nanozyme activity. The characterizations of transition electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) presented that the dropping of WO3 accelerated the electron transfer and redistribution capacity of WO3/Mn3O4, thus exhibiting excellent oxidase and peroxidase activities. Density functional theory (DFT) revealed that WO3/Mn3O4 effectively increased the adsorption capacity of O2 molecules and drastically reduced the kinetic energy potential of the reaction-limiting step in the oxidase-like activity. An "on-off-on" colorimetric and intelligent biosensing platform for epinephrine and Ag+ was successfully constructed. It was used to visualize and monitor epinephrine levels in human serum with a linear range of 0.075–65 µM and a detection limit of 0.055 µM. The mechanism of detection was revealed using infrared spectroscopy. Moreover, WO3/Mn3O4 took more readily to obtain the electrons of epinephrine than 3,3′,5,5′-tetramethylbenzidine. Therefore, the colorimetric sensor of epinephrine on the basis of the oxidase of WO3/Mn3O4 had a promising future in the biomedical field.