Porous Gold-Nanoparticle−CaCO₃ Hybrid Material:  Preparation, Characterization, and Application for Horseradish Peroxidase Assembly and Direct Electrochemistry

Gold nanoparticles (AuNPs) were assembled on the surface of porous calcium carbonate microspheres (CaCO₃) in a neutral aqueous solution through electrostatic interaction. The resulting gold-nanoparticle−CaCO₃ hybrid material (AuNP−CaCO₃) was characterized and expected to offer a promising template for enzyme immobilization and biosensor fabrication because of its satisfying biocompatibility and improved properties. It was conjugated with horseradish peroxidase (HRP) to fabricate HRP−AuNP−CaCO₃ bioconjugates, which were then embedded into a silica sol−gel matrix to construct a novel biosensor. Because of the synergic effect of CaCO₃ microspheres and AuNPs, direct electron transfer of HRP was observed at this biosensor. The biosensor exhibited a fast amperometric response to H₂O₂, with a linear range of 4.0 × 10^-5 to 8.0 × 10^-3 mol/L. The detection limit was 1.0 × 10^-6 mol/L based on S/N = 3.