Electrochemical determination of hydrogen peroxide production by isolated mitochondria: A novel nanocomposite carbon–maghemite nanoparticle electrode

A simple carbon paste electrode modified with novel maghemite (γ-Fe2O3) nanoparticles, characterized by a mean diameter of about 10 nm and specific surface properties (called surface active maghemite nanoparticles, SAMNs) has been developed. The electrode is able to catalyze the electro-reduction of hydrogen peroxide at low applied potentials (−0.1 V vs. SCE). In order to improve the electrocatalytic properties of the modified electrode and to protect electrode surface from fouling due to the presence of biological materials, a surfactant, namely cetyltrimethylammonium bromide, was introduced, as monomolecular layer, on electrode surface. At −0.1 V, the sensitivity of the modified nanocomposite electrode was 58 nA μM−1 cm−2, with a detection limit of 2.78 μM, in the 0.01–1.5 mM H2O2 concentration range, revealing to be one of the most sensitive electrodes described in literature. The resulting electrode was used to determine native monoamine oxidase activity on intact mitochondria suspensions, allowing the determination of catalytic parameters of the enzyme. Following this new electrochemical methodology, we implemented a novel electrochemical assay for the investigation of aerobic metabolism in preparations of isolated mitochondria revealing active H2O2 production by respiring rat liver mitochondria. The present work demonstrates the feasibility of these novel maghemite nanoparticles modified electrode as efficient hydrogen peroxide electro-catalyst, for the application on biological samples at low applied potentials.