CHARACTERIZATION OF OCTADECANETHIOL-COATED GOLD ELECTRODES AS MICROARRAY ELECTRODES BY CYCLIC VOLTAMMETRY AND AC-IMPEDANCE SPECTROSCOPY

Organized monolayers of octadecanethiol on gold are examined by cyclic voltammetry (CV) and ac impedance spectroscopy (ACIS) in electrolytes containing 1-electron redox couples. Pinholes in the monolayer lead t o voltammetric behavior resembling that of a microarray electrode. Con tour plots are given for linear scan voltammetric parameters (peak cur rent, peak potential and half-peak potential) from the theoretical tre atment of microarray electrodes. The theory of ac impedance spectrosco py is developed for a microarray electrode with the area fraction of a ctive sites less than 0.1. The behavior of monolayer-coated electrodes conforms qualitatively to the predictions for microarray electrodes w ith pinhole radii of ca. 0.1-10 mum and pinhole separations of 1-100 m um, but significant deviations from the predictions are observed. The deviations are discussed in terms of the nonuniform distribution of th e diameter and separation of the pinholes. ACIS data in particular sug gest that the pinholes are grouped in patches.