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

Abstract

Horseradish peroxidase (HRP), a natural enzyme, consists of a Fe^III ion, which plays the role as an active center of the enzyme, wherein the binding of H₂O₂ to the Fe^III ion creates an octahedral configuration around Fe^III, 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 Fe^III 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 (K_m) 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 μM for H₂O₂ and 40 μM 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.