Enhancing enzymatic activity of Mn@Co3O4 nanosheets as mimetic nanozyme for colorimetric assay of ascorbic acid

Abstract

In nanozyme-based assays, increasing enzymatic activity is very desirable for enhancing sensitivity and lowering the detection limit. In this study, novel Mn doped cobalt oxide nanosheets (Mn@Co₃O₄ NSs) were synthesized by hydrothermal process. The obtained Mn@Co₃O₄ possessed enhanced dual-enzyme mimetic, oxidase and peroxidase, and can catalytically oxidize of 3, 3', 5, 5'-tetramethylbenzidine (TMB), to a blue product of oxidized TMB. The enzyme kinetics were well-described mathematically using a common Michaelis-Menten and Lineweaver Burk model. The enzyme kinetics constant (K_m) was found to be 0.15 mM, which is relatively low comparing with pure Co₃O₄ nanosheets (0.35 mM) and natural enzyme HRP (0.434 mM). Therefore, the efficient colorimetric method was achieved for determination of H₂O₂ and ascorbic acid. The limit of detection (LOD) of H₂O₂ was 8.0 μM and the linear range was 20-200 μM based on direct turn on of the peroxidase-like activity of Mn@Co₃O₄. While, for ascorbic acid detection based on turn-off approach, the linearity range for the ascorbic acid was 1-8 μM with LOD of 0.4 μM. Moreover, the colorimetric system exhibited good stability and selectivity toward the detection of ascorbic acid effectively in real samples (vitamin C tablets) with satisfactorily accuracy and precision.

Keywords: Ascorbic acid; Dual mimetic enzyme; Mn doped Co(3)O(4); Nanosheets.