Electrochemistry of methylene blue at an alkanethiol modified electrode

Gold surfaces were derivatized with decanethiol. The electrochemistry of methylene blue at these modified electrodes was investigated in function of the gold cleaning process and compared with the results obtained at a bare gold electrode. Cyclic voltammetry at low methylene blue concentrations (cMB ≤ 16 μM) yielded surface behavior data. The properties of the film vary with the electrode pretreatment. Without electrochemical cleaning step, the standard potential at a gold electrode modified with 1-decanethiol is nearly the same as on a bare gold electrode. On the other hand, when the electrode is electrochemically cleaned before adsorption of the alkanethiols, the standard potential of MB appears at a more positive value than on gold electrode. The electrochemical pretreatment promotes the penetration of both oxidized and reduced forms of MB into the monolayer. The insertion of methylene blue into the monolayer was fitted using a Langmuir isotherm adsorption. This supports a model where the methylene blue molecules partitioned into hydrophobic pockets of the film.