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, Fe3O4@MIL-100(Fe), which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to produce a blue product. The combination of Fe3O4 and MIL-100(Fe) can remarkably enhance peroxidase-like activity. The catalytic behavior of Fe3O4@MIL-100(Fe) followed Michaelis-Menten equation and the affinity of Fe3O4@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 H2O2. As H2O2 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, Fe3O4@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.