Ultrathin 2D-MOFs for dual-enzyme cascade biocatalysis with sensitive glucose detection performances

In recent years, two-dimensional nanosheet metal-organic frameworks (2D MOFs) have been widely considered as promising carriers for enzyme immobilization owing to their large surface area, designable and tunable structures, and other properties that enhance enzyme loading and modulate interactions with enzymes. In this study, a series of ultrathin 2D M-TCPP (M = Co, Ni, Zn, Cu) nanosheets were synthesized employing a surfactant-assisted bottom-up approach, and the effect of solvent ratio on the morphology and properties of 2D MOFs was explored. After systematic characterization, Cu-based 2D MOFs with large specific surface areas and excellent water stability was selected as the carrier for the co-immobilization of glucose oxidase (GOx) and horseradish peroxidase (HRP). The effects of adsorption and covalent immobilization strategies on bis-enzyme loading and enzyme activity, as well as their applications in rapid glucose detection, were systematically investigated. The results showed that A-CTGH and C-CTGH owned enzyme loadings of 187.9 and 249.1 mg/g, respectively, and exhibited superior enzymatic activity when exposed to harsh environments compared to free enzymes. In addition, the covalently immobilized biocatalyst based on GOx demonstrated a more sensitive glucose detection performance, including a wide linear range from 5.0 to 16 μM with a detection limit of 0.6 μM.