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Rational design of high-performance nanozyme is of great significance for sensing applications. Here, N-doped carbon nanocages containing Co-N x active sites (CoN x -NC) were fabricated by simple acid etching of Co@NC, which is the product of Co–Co Prussian blue analogues carbonized in an N2 atmosphere. Both optimized Co@NC-650 and CoN x -NC-650 exhibit catalase- and oxidase-like properties. They rapidly decompose H2O2 into O2 and oxidize colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into a blue product. This enables them with no peroxidase-like activity. The oxidase-like activity of CoN x -NC-650 is 3.9 times that of unetched Co@NC-650. The acid treatment dissolves Co nanoparticles generated during carbonization, forming extra mesoporous structures and increasing the exposure of more Co-N x active species. The Michaelis–Menten constant for CoN x -NC-650 with a TMB substrate is 0.186 mM, which is 3.2 times lower than that of oxidase-mimicking CeO2 nanoparticles, suggesting a higher affinity to TMB. Given its excellent oxidase-like activity, the CoN x -NC-650 was used to sensitively and selectively determine acetylcholinesterase (AChE) activity based on thiocholine inhibition of the TMB color reaction. Thiocholine is produced via hydrolysis of acetylthiocholine catalyzed by AChE. The colorimetric biosensor has a linear response to AChE over 0.6–800 mU L–1 concentration range and a detection limit (3σ) of 0.2 mU L–1. The assay was successfully applied to determine AChE activity in biological samples.

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Two-dimensional (2D) nanomaterials are attractive in catalysis due to their rich accessible active sites. Iron-based metal organic framework (MOF) is one of promising nanozymes because of its iron center and...