Fe3O4@C magnetite nanocomposite: an artificial peroxidase nanozyme for the development of a colorimetric glucose biosensor

Horseradish peroxidase (HRP), a natural enzyme, consists of a FeIII ion, which plays the role as an active center of the enzyme, wherein the binding of H2O2 to the FeIII ion creates an octahedral configuration around FeIII, leading to the decomposition of the -O-O- bond of H2O2. Based on this considering, here, we propose amorphous-carbon-functionalized Fe3O4 nanoparticles (Fe3O4@C) that serve as a peroxidase nanozyme with FeIII and exhibits peroxidase-like catalytic activity. In this work, Fe3O4@C was synthesized via a simple hydrothermal process from a suspension of Fe3O4 nanoparticles and glucose solution. The peroxidase-mimicking activity of Fe3O4@C was demonstrated following the Michaelis-Menten and Lineweaver-Burk equations of the enzymatic model. At optimized conditions, Fe3O4@C showed stronger catalytic activity than HRP, with Michaelis-Menten constants (Km) 0.052 mM and 0.004 mM for the H2O2 substrate and TMB co-substrate, respectively. Using Fe3O4@C as a replacement for HRP, a colorimetric chemical sensor for H2O2 sensing and a colorimetric biosensor for glucose detection were constructed, and they exhibited high selectivity and sensitivity with an LOD of 20 mu M for H2O2 and 40 mu M for glucose. The applicability of the glucose biosensor was also tested in real samples, including a 5% intravenous glucose solution and human blood serum, revealing high recovery rates.