Rational design of ZIF-67 derived hollow nanozyme through a general strategy for biosensing

Metal-organic frameworks (MOF)-based nanozymes have aroused enormous attention due to their great application potential. However, diverse MOF nanozymes composed of different metal elements, such as Fe, Cu, Ce, etc., need to be prepared respectively, which is quite cumbersome and time-consuming. Therefore, the development of a general preparation strategy is very worthy of expectation. Here, we reported a general strategy for synthesizing multiple M-PA polyhedral networks (M: metal ions, PA: phytate) using ZIF-67 as a template by a two-step strategy of etching and cation exchange. The prepared M-PA was micropolyhedral nanomaterials featured with hollow structure by a series of characterization methods. Enzyme activity tests showed that M-PA (M = Fe3+, Cu2+, Ce4+) possessed excellent enzyme-like activity. Among them, Ce4+-PA had oxidase-like activity, while Fe3+-PA and Cu2+-PA showed peroxidase-like activity. Taking Fe3+-PA as an example, further study was carried out. The enzyme kinetics study showed that the Km value of Fe3+-PA for H2O2 was lower than HRP and Fe3O4, implying that Fe3+-PA possessed a stronger affinity for H2O2. The mechanism investigation revealed that OH and O2− are the main reactive oxygen species for the peroxidase-like activity of Fe3+-PA. Based on Fe3+-PA nanozyme, a colorimetric sensing platform for assessing total antioxidant capacity (TAC) was established, in which the detection limits of ascorbic acid (AA), L-cysteine (L-Cys), and glutathione (GSH) were 0.56 µM, 0.79 µM, and 1.17 µM, respectively. The proposed assay was successfully applied to the detection of TAC in real samples. This work provides a general and feasible strategy for the rational synthesis of hollow nanozymes.