A bimetallic Co/Mn metal–organic-framework with a synergistic catalytic effect as peroxidase for the colorimetric detection of H2O2

Abstract

Metal–organic frameworks (MOFs) with a metal coordination structure mimicking that of enzymes have been widely applied in the sensing field for bioassays, and most of the reports focus on single-metal MOFs. However, bimetallic MOFs have fascinating catalytic capabilities due to their bimetallic coordination. Herein, a two-dimensional sheet-like bimetallic Co/Mn-based MOF (Co/Mn-MOF) with peroxidase-like activity was synthesized through a one-step hydrothermal method to accelerate the decomposition of H₂O₂ with the generation of ˙OH, which further oxidized the classic chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) into oxTMB. The Michaelis–Menten constants (K_m) and maximum initial velocities (V_max) of the catalyst were found to be 0.27 mM and 1.64 × 10⁻⁷ M s⁻¹ for TMB and 0.24 mM and 5.80 × 10⁻⁷ M s⁻¹ for H₂O₂, respectively. Accordingly, we successfully utilized Co/Mn-MOF-1-1-150 to establish a colorimetric detection platform for the detection of H₂O₂. A linear absorbance response ranging from 1 to 100 μM with the limit of detection of 0.85 μM (S/N = 3) was obtained under the optimized conditions. The LOD of our catalyst is comparable to that of other MOF-based enzyme mimics for colorimetric detection; this can be ascribed to the synergistic catalytic effect between its two metals, its two-dimensional structure with a small diffusion barrier for the substrate molecules, and large exposed surface area. More importantly, using the proposed sensing method, the determination of H₂O₂ released by living cells and in spiked water samples was achieved. This revealed that the as-prepared bimetallic Co/Mn-MOF could be a promising candidate as a catalytic material due to its peroxidase activity.