Characterization of the Chemical Architecture of Carbon-Fiber Microelectrodes. 3. Effect of Charge on the Electron-Transfer Properties of ECL Reactions
Two techniques, cyclic voltammetry and the microscopic imaging of electrochemically generated chemiluminescence (ECL), have been used to evaluate the effectiveness of various electrochemical pretreatments on the electron-transfer properties of carbon-fiber microelectrodes. The surfaces of carbon-fiber microelectrodes were electrochemically treated to produce different levels of surface oxides in the following manner: after normal polishing and cleaning in hot toluene and water, the carbon surface was activated by applying a cyclic potential from -0.2 to 2.0 V at a frequency of 50 Hz for 3 s in solutions of varying pH: 1M HCl, pH 7.4 and pH 12.0 phosphate buffers. Cyclic voltammetry was employed to elucidate the effect of the surface pretreatment on the overall voltammetric properties of the different pretreatment methods. The ECL emission intensity was imaged with resolution on the submicrometer scale with a conventional fluorescence microscope equipped with a cooled, slow-scan CCD camera. In addition to investigating pretreatment effects with luminol, we have also examined the ECL properties of a positively charged species, ruthenium tris (2,2'-bipyridine) dichloride hexahydrate, whose luminescent properties are also well documented. Such information is not only invaluable for the rational design of surface-modified ultramicroelectrodes, but it can also yield considerable information concerning the surface interactions influencing organic electron-transfer reactions at carbon surfaces.