Co Nanoparticles Embedded in 2D N-Doped Porous Carbon Nanosheets for Evaluating Acetylcholinesterase Activity

Here, we reported a facile strategy to prepare Co nanoparticles (NPs) encapsulated in two-dimensional (2D) N-doped porous carbon nanosheets (2D Co/NC) via pyrolyzing Zn/Co bimetallic metal–organic framework (MOF) nanosheets, which were prepared in aqueous solution. The successful synthesis of Zn/Co bimetallic MOF nanosheets and 2D Co/NC was demonstrated by various characterization techniques. The optimized 2D Co0.6/NC-700 and three-dimensional (3D) Co0.6/NC-700 show catalase- and oxidase-like activities. They can break down H2O2 into O2 and oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue product, while the former displays superior performance to its 3D Co0.6/NC-700 aggregated nanoparticles. Specifically, the oxidase-mimicking activity and catalase-like activity of 2D Co0.6/NC-700 are 1.64-fold and 6.9-fold those of 3D Co0.6/NC-700, respectively. Relative to 3D Co0.6/NC-700 aggregates, the improvement of the catalytic activity of 2D Co0.6/NC-700 is likely ascribed to its 2D leaf-like structure with more accessible dispersed active sites and the interaction between Co NPs and N-doped carbon nanosheets. 2D Co0.6/NC-700 displayed superior oxidase-like activity with a low Michaelis–Menten constant (Km) of 0.35 mM. Interestingly, in the presence of both acetylcholinesterase (AChE) and acetylthiocholine (ATCh), the oxidase-like activity was suppressed because of the generation of thiocholine, which led to the fading of the TMB color reaction. On this basis, a colorimetric assay was developed for the determination of AChE activity. 2D Co0.6/NC-700 displayed excellent detection performance in AChE activity, with a linear detection range of 0.0002–0.8 U L–1 and a low detection limit of 0.0002 U L–1. Remarkably, the method showed good selectivity to AChE, and other coexisting substances had minor interference. The method was satisfactorily utilized to determine the AChE activity in real samples.