Preparation and Application of Mediator‐Free H 2 O 2 Biosensors of Graphene‐Fe 3 O 4 Composites

Graphene‐Fe 3 O 4 (G‐Fe 3 O 4 ) composites were prepared with a solvothermal method for the immobilization of horseradish peroxidase (HRP) to construct a mediator‐free H 2 O 2 biosensor. The morphology and structure of the G‐Fe 3 O 4 composites were analyzed by TEM, SEM, and XRD. Chitosan (CH) was utilized to disperse the composites, and the mixture of CH, G‐Fe 3 O 4 and HRP was spin‐coated on an indium tin oxide (ITO) electrode to form a biocomposites film. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) demonstrated the fast electron transfer process between HRP and the electrode. The resulted H 2 O 2 biosensor exhibited a rapid response upon the addition of H 2 O 2 , a high sensitivity of 132 µA mM −1  cm −2 and a low detection limit of 6×10 −7  M. The linear range of the biosensor is from 5×10 −6 to 3.81×10 −3 M ( r =0.997). Such interesting G‐Fe 3 O 4 composites with easy preparation and low cost can provide a novel matrix for enzyme immobilization to construct biosensors with higher performance.