Imaging microelectrodes with high-frequency electrogenerated chemiluminescence

The chemiluminescence arising from reaction of electrogenerated intermediat es of 9,10-diphenylanthracene (DPA) has been used to generate images of mic roelectrodes with dimensions in the micrometer range. The experimental cond itions were optimized to ensure high luminescent intensity with sharp focus ing of the reaction zone to enable good optical resolution. The solution em ployed, benzonitrile (BN) containing 0.1 M tetrabutylammonium hexafluoropho sphate, promotes high intensity because it enables dissolution of a high co ncentration (>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 w as 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 poten tial pulses that maintain the reaction zone in close proximity to the elect rode. The images reveal that the electrode areas have quite different topog raphy than inferred from steady-state cyclic voltammograms.