Promoting sensitive colorimetric detection of hydroquinone and Hg via ZIF-8 dispersion enhanced oxidase-mimicking activity of MnO nanozyme.

Reducing the agglomeration and improving the dispersibility in water of two-dimensional (2D) nanozymes is one of the effective ways to improve their enzyme-like activity. In this work, we propose a method by constructing zeolitic imidazolate framework-8 (ZIF-8)-dispersed 2D manganese-based nanozymes to achieve the specific regulated improvement of oxidase-mimicking activity. By in-situ growth of manganese oxides nanosheets of MnO(1), MnO(2) and MnO on the surface of ZIF-8, the corresponding nanocomposites of ZIF-8 @MnO(1), ZIF-8 @MnO(2), and ZIF-8 @MnO were prepared at room temperature. The Michaelis-Menton constant measurements indicated that ZIF-8 @MnO(1) exhibits best substrate affinity and fastest reaction rate for 3,3',5,5'-tetramethylbenzidine (TMB). The ZIF-8 @MnO(1)-TMB system was exploited to detection of trace hydroquinone (HQ) based on the reducibility of phenolic hydroxyl groups. In addition, by employing the fact that the cysteine (Cys) with the excellent antioxidant capacity can bind the Hg based on the formation of "S-Hg" bonds, the ZIF-8 @MnO(1)-TMB-Cys system was applied to detection of Hg with high sensitivity and selectivity. Our findings not only provide a better understanding of the relationship between dispersion of nanozyme and enzyme-like activity, but also provide a general method for the detection of environmental pollutants using nanozymes.