Core-shell structured Ag@C for direct electrochemistry and hydrogen peroxide biosensor applications.

Ag@C core-shell nano-composites have been prepared by a simple one-step hydrothermal method and are further explored for protein immobilization and bio-sensing. The electrochemical behavior of immobilized horseradish peroxidase (HRP) on Ag@C modified indium-tin-oxide (ITO) electrode and its application as H₂O₂ sensor are investigated. Electrochemical and UV-vis spectroscopic measurements demonstrated that Ag@C nano-composites provide excellent matrixes for the adsorption of HRP and the entrapped HRP retains its bioactivities. It is found that on the HRP-Ag@C/ITO electrode, HRP exhibited a fast electron transfer process and good electrocatalytic reduction toward H₂O₂. Under optimum experimental conditions the biosensor linearly responds to H₂O₂ concentration in the range of 5.0×10⁻⁷-1.4×10⁻⁴ M with a detection limit of 2.0×10⁻⁷ M (S/N=3). The apparent Michaelis-Menten constant (K(app)(M)) of the biosensor is calculated to be 3.75×10⁻⁵ M, suggesting high enzymatic activity and affinity toward H₂O₂. In addition, the HRP-Ag@C/ITO bio-electrode shows good reproducibility and long-term stability. Thus, the core-shell structured Ag@C is an attractive material for application in the fabrication of biosensors due to its direct electrochemistry and functionalized surface for efficient immobilization of bio-molecules.