DOI: 10.1002/adma. 201600108 with the heme protein Mb. Later, Zhou and co-workers synthesized a series of metalloporphyrin Fe-MOFs (PCN-600 (M), M= Mn, Fe, Co, Ni, and Cu), among which the PCN-600 (Fe) was successfully used as an effective enzymatic mimic to catalyze the co-oxidation reaction.[8] However, the work on the ion porphyrin-based MOFs used as enzymatic mimic was only focused on the 3D bulk MOF crystals. Their large volume led to the slow diffusion rate and thus limited the accessibility of large-sized substrate molecules to the active sites inside the 3D bulk MOFs.[8, 9]

Compared to the conventional 3D bulk MOF crystals, 2D MOF nanosheets, which have attracted increasing research interest recently,[10–14] possess larger surface area and more accessible active sites for the substrate molecules with a smaller diffusion barrier.[10] Conventionally, single-or few-layer 2D MOF nanosheets can be prepared by various methods, such as ultrasonication exfoliation,[11] liquid exfoliation,[12] three-layer synthesis,[10] layer-by-layer growth,[13] and our recently developed surfactant-assisted synthesis.[14] Among them, the last one allows for the high-yield and large-amount production of 2D MOF nanosheets with thickness of sub-10 nm.[14] Here, for the first time, a heme-like ligand, TCPP (Fe)(Fe (III) tetra (4-carboxyphenyl) porphine chloride), is used for the synthesis of ultrathin 2D bimetallic MOF nanosheets with thickness of sub-10 nm. Three kinds of metal nodes (Co, Cu, and Zn) are used for preparation of a series of 2D M-TCPP (Fe) nanosheets (M= Co, Cu, and Zn) by using the surfactant-assisted synthetic method.[14] Importantly, these 2D M-TCPP (Fe) nanosheets can be assembled into multilayer films on electrodes through a Langmuir–Schäfer method.[15] As a proof-of-concept application, the obtained 2D M-TCPP (Fe) nanosheet-based film is used as a novel electrochemical platform for the detection of H2o 2, which exhibits higher sensitivity compared to the previously reported natural heme proteins. Moreover, the fabricated 2D Co-TCPP (Fe) nanosheet-based sensor can be used for the real-time tracking of H2o 2 secreted by live cells. To illustrate our synthesis procedure, the Co-TCPP (Fe) MOF, which is isoreticular to PPF-1 (Co),[16] was used as an example. The Co-TCPP (Fe) MOF was constructed by using TCPP (Fe) instead of TCPP (tetrakis (4-carboxyphenyl) porphyrin)[16] as ligand. Its crystalline structure consists of four Co 2 (COO) 4 paddlewheel metal nodes interconnected by one TCPP (Fe) molecule (Figure 1a), composing layers which stack in an AB packing pattern (Figure 1 b). As known, the conventional solvothermal method mainly produced well-defined cubic bulk