An electrochemical sensor system 160 for sensing free radicals or materials which generate free radicals in solution includes electrode member 100 including a cerium oxide nanoparticle coated sensor electrode (working electrode) 108/105, counter electrode 120, and optional reference electrode 130. A solution or material having an associated solution to be analyzed provides electrolytes to electrically couple the working electrode to the counter electrode. Electronics 170 are connected to at least one of the working and counter electrodes for measuring and amplifying an electrical current signal generated by reduction or oxidation occurring at the working electrode, wherein in a presence of free radicals an electrical current signal flows between the working electrode and the counter electrode. The system can be used to sense the presence of hydrogen peroxide
