Characterization of the Chemical Architecture of Carbon-Fiber Microelectrodes. 3. Effect of Charge on the Electron-Transfer Properties of ECL Reactions

Abstract

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.

Electrochemiluminescent Systems as Devices and Sensors

“…221 ECL has been also used to image ultramicroelectrodes and arrays electrodes. [219][220][221][222][223] The ECL signal from the annihilation reaction between Ru(bipy) 3 þ and Ru(bipy) 3 3 þ species, generated at a platinum band microelectrodes separated by a micrometric insulating gap, has been observed with use of a confocal microspectrometer. It has allowed in situ photon detection of the ECL reaction with micrometric spatial resolution and the observation of the photon source distribution in the vicinity of the gap between the microelectrodes.…”

Imaging Analysis Based on Electrogenerated Chemiluminescence

“…The effect of surface oxide groups on the electron-transfer for both luminol and Ru(bpy) 3 2? has also been studied, suggesting that luminol and Ru(bpy) 3 2? were oxidized at different sites on the carbon-fiber electrode surface [64]. Wightman et al have performed the activity imaging at microelectrode surfaces [65] and observed the nonuniform current density [66] by ECL generated upon biasing high-frequency potential pulses, which could maintain the reaction zone in close proximity to the electrode and thus prevent reactants from diffusing away from one another.…”

Mapping Electrochemiluminescence as Generated at Double‐Band Microelectrodes by Confocal Microscopy under Steady State

“…Since the generated light intensity is generally proportional to the concentration of the emitting species, ECL-active species can thus be used as labels on biological molecules for the design of high-density immunoassays and DNA analysis. [23,24] ECL reactions allow the visualization of the functional areas of electrodes, [15,[25][26][27] the examination of active sites for electron transfer [28][29][30] or even the imaging of samples by scanning the surface with an ultramicroelectrode tip generating ECL as a light source. [14,31,32] In this last application, the resolution of the ECL emission achieved, depends strongly on the size of the spatial region where ECL is generated.…”