pH-responsive dual-enzyme mimics based on hollow metal organic framework-derivatives β-Co(OH) 2 for multiple colorimetric assays.

A hollow metal organic framework derivative β-Co(OH) 2  has been prepared, which possesses oxidase and peroxidase-like activities. Oxidase-like activity is derived from the generation of free radicals, and peroxidase-like activity is related to the electron transfer process. Unlike other nanozymes with dual enzyme-like activities, β-Co(OH) 2 possesses pH-responsive enzyme-like activities, among which the β-Co(OH) 2 exhibits superior oxidase and peroxidase-like activities under pH of 4 and 6, respectively, which could avoid mutual interference between multiple enzymes. Based on the phenomenon that enzyme-like activities of β-Co(OH) 2 can catalyze colorless TMB to generate blue oxidized TMB (oxTMB) with absorption peak at 652 nm, the sensors integrating total antioxidant capacity and H 2 O 2 quantification were developed. The oxidase-like activity-based colorimetric system has a sensitive response to ascorbic acid, Trolox, and gallic acid, in which the limit of detection for those antioxidant substances was 0.54 μM, 1.26 μM, and 14.34 μM, respectively. The sensors based on peroxidase-like activity had low limit of detection of 1.42 μM for H 2 O 2 and a linear range of 5-1000 μM. The proposed method can be well applied to the detection of the total antioxidant capacity of kiwi, Vc tables, orange and tea extract with high accuracy, and H 2 O 2 determination in milk and glucose detection in beverages with satisfactory recovery (within 97-106%).