An electrochemical fractal analysis of three types of colloidal Au nanoparticle electrodes is described. One type of electrode comprises multilayers of 12-nm diameter colloidal Au particles on glass substrates; another type consists of analogous films grown on conductive An substrates. Plots of log(I) vs. log(t) data from electrochemical potential step experiments were used to determine D-f the fractal dimension. On the Au substrate, D-f ranged from 2.16 to 2.47 for films consisting of 7-13 colloidal Au layers, respectively, while for the glass substrate D-f varied from 1.54 to 2.33 over the same range of layers. A third type of Au nanoparticle-based electrode was prepared by enlargement of nanoparticles in Au colloid monolayers by exposure to NH2OH/Au3+. For these samples, D-f varied from ca. 1.2 to 2.0. D-f determination by atomic force microscopy gave values in the range of 2.3-2.4 for both types of nanoparticle electrodes on glass substrates, regardless of Au film thickness. (C) 2003 Elsevier B.V. All rights reserved.