Imaging microelectrodes with high-frequency electrogenerated chemiluminescence

The chemiluminescence arising from reaction of electrogenerated intermediates of 9,10-diphenylanthracene (DPA) has been used to generate images of microelectrodes with dimensions in the micrometer range. The experimental conditions were optimized to ensure high luminescent intensity with sharp focusing of the reaction zone to enable good optical resolution. The solution employed, benzonitrile (BN) containing 0.1 M tetrabutylammonium hexafluorophosphate, promotes high intensity because it enables dissolution of a high concentration (>25 mM) of DPA. In addition, radical anions of BN can serve as a reagent reservoir to ensure efficient reaction of DPA radical cations to the singlet excited state. Under these conditions the measured intensity was 3.2 x 10(5) photons/s per mu m(2) of electrode area with a 1 kHz square-wave excitation. Lateral resolution is controlled by the use of rapid potential pulses that maintain the reaction zone in close proximity to the electrode. The images reveal that the electrode areas have quite different topography than inferred from steady-state cyclic voltammograms.