Direct electrochemistry of nanoparticulate Fe2O3 in aqueous solution and adsorbed onto tin-doped indium oxide

Nanoparticulate iron oxides occur naturally, for example, in soil, water, and in the cytoplasm of living cells. The redox properties and detection of these nanoparticles are therefore of considerable importance. Understanding and mimicking nanoparticle-based redox reactions may lead to new types of water-based electrochemical processes. In this study, the electrochemical detection of 4-5 nm diameter Fe2O3 nanoparticles dissolved in aqueous buffer solutions is investigated as a model system. Voltammetric experiments with nanoparticulate Fe2O3 are reported based on two complementary approaches: (i) Fe2O3 nanoparticles adsorbed onto tin-doped indium oxide (ITO) electrodes are shown to give well-defined voltammetric reduction responses and (ii) hydrodynamic voltammety in the presence of fast (24 kHz ultrasound-enhanced) mass transport is shown to allow the direct detection of Fe2O3 nanoparticles in solution. Both the adhesion and the electrochemical reactivity of Fe2O3 nanoparticles at ITO electrode surfaces are strongly affected by the solution composition and the pH.