Direct electrochemistry of horseradish peroxidase based on biocompatible carboxymethyl chitosan–gold nanoparticle nanocomposite

The nanocomposite composed of carboxymethyl chitosan (CMCS) and gold nanoparticles was successfully prepared by a novel and in situ process. It was characterized by transmission electron microscopy (TEM) and Fourier transform infrared spectrophotometer (FTIR). The nanocomposite was hydrophilic even in neutral solutions, stable and inherited the properties of the AuNPs and CMCS, which make it biocompatible for enzymes immobilization. HRP, as a model enzyme, was immobilized on the silica sol–gel matrix containing the nanocomposite to construct a novel H2O2 biosensor. The direct electron transfer of HRP was achieved and investigated. The biosensor exhibited a fast amperometric response (5 s), a good linear response over a wide range of concentrations from 5.0 × 10−6 to 1.4 × 10−3 M, and a low detection limit of 4.01 × 10−7 M. The apparent Michaelis–Menten constant (KMapp) for the biosensor was 5.7 × 10−4 M. Good stability and sensitivity were assessed for the biosensor.