Fe 3 O 4 @C magnetite nanocomposite: an artificial peroxidase nanozyme for the development of a colorimetric glucose biosensor

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 H 2 O 2 to the Fe III ion creates an octahedral configuration around Fe III , leading to the decomposition of the –O–O– bond of H 2 O 2 . Based on this considering, here, we propose amorphous-carbon-functionalized Fe 3 O 4 nanoparticles (Fe 3 O 4 @C) that serve as a peroxidase nanozyme with Fe III and exhibits peroxidase-like catalytic activity. In this work, Fe 3 O 4 @C was synthesized via a simple hydrothermal process from a suspension of Fe 3 O 4 nanoparticles and glucose solution. The peroxidase-mimicking activity of Fe 3 O 4 @C was demonstrated following the Michaelis–Menten and Lineweaver–Burk equations of the enzymatic model. At optimized conditions, Fe 3 O 4 @C showed stronger catalytic activity than HRP, with Michaelis–Menten constants ( K m ) 0.052 mM and 0.004 mM for the H 2 O 2 substrate and TMB co-substrate, respectively. Using Fe 3 O 4 @C as a replacement for HRP, a colorimetric chemical sensor for H 2 O 2 sensing and a colorimetric biosensor for glucose detection were constructed, and they exhibited high selectivity and sensitivity with an LOD of 20 μM for H 2 O 2 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.