Novel core–shell Fe₃O₄@poly(dopamine) magnetic nanoparticles were prepared through an in situ self-polymerization method. The hybrid nanomaterial showed an average core diameter of 11 ± 3 nm and a polymer thin film thickness of 1.8 ± 0.2 nm. The core–shell nanoparticles were employed as solid supports for the covalent immobilization of horseradish peroxidase (HRP), and the resulting biofunctionalized magnetic nanoparticles were employed to construct an amperometric biosensor for H₂O₂. The enzyme biosensor showed a high sensitivity of 442.14 mA M⁻¹ cm⁻², a low limit of detection of 182 nM, a wide linear range from 6.0 × 10⁻⁷ to 8.0 × 10⁻⁴ M and high stability for 1 month.

Bovine trypsin immobilized on glyoxyl agarose and submitted to different inactivation conditions produce different conformations.