ELECTRODE-REACTION OF METHYLENE-BLUE AT AN ALKANETHIOL-MODIFIED GOLD ELECTRODE AS CHARACTERIZED BY ELECTROREFLECTANCE SPECTROSCOPY

The electrode reaction of methylene blue (MB) at a polycrystalline gol d electrode modified with a self-assembled monolayer of n-dodecanethio l was analyzed by using voltammetric and electroreflectance (ER) techn iques. The results for the gold electrode modified with a dodecanethio l monolayer were compared with the data obtained at a bare gold electr ode and a gold electrode modified with butanethiol, thiophene, or sulf ur. The ER spectrum of MB at the gold electrode modified with dodecane thiol monolayer was in accord with the difference absorption spectrum between reduced and oxidized forms of MB in the solution. The ER spect rum of MB at the bare gold electrode had a different structure. We con cluded that MB molecules were partitioned into the dodecanethiol monol ayer interior on the gold electrode surface. The MB molecules, however , were not in direct contact with the gold surface when the electron t ransfer takes place.