The redox mechanism of phenothiazine is a two electron
process. In cyclic voltammograms of the mediator in a γ-
aminopropyl-triethoxysilane membrane, the two sets of peaks
are clearly observed. Dependence of the common peak
potentials on solution pH points to the two electron−two
proton reaction. Despite the oxidized form of phenothiazine is
charged and likely water-soluble, the cyclic voltammograms of
the mediator in siloxane gels are rather stable, displaying more
than 90% of the initial peak current value even after 100 cycles
(data not shown).