Metal-organic framework coated Fe3O4 magnetic nanoparticles with peroxidase-like activity for colorimetric sensing of cholesterol

Artificial enzymes have received much attention because of easy access, low cost and good stability. In this work, we report on a core–shell artificial peroxidase, namely, Fe 3 O 4 @MIL-100(Fe), which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H 2 O 2 to produce a blue product. The combination of Fe 3 O 4 and MIL-100(Fe) can remarkably enhance peroxidase-like activity. The catalytic behavior of Fe 3 O 4 @MIL-100(Fe) followed Michaelis–Menten equation and the affinity of Fe 3 O 4 @MIL-100(Fe) to substrate was higher than horseradish peroxidase. Under the optimal conditions, the absorbance of oxidized TMB at 652   nm is linearly correlated with the concentration of H 2 O 2 . As H 2 O 2 is the oxidative product of cholesterol in the presence of cholesterol oxidase, a sensitive and selective method of cholesterol detection was also developed. As low as 0.8   μM of cholesterol could be detected with a linear range from 2 to 50   μM ( r   =   0.999). The proposed method was successfully applied to the detection of cholesterol levels in serum samples. As an artificial peroxidase, Fe 3 O 4 @MIL-100(Fe) has advantages of high catalytic efficiency, low cost, good stability, easy preparation and storage. This work demonstrates that MOF-based materials hold great promise for applications in bioanalysis.