The adsorptive accumulation of ATX-I, a mycotoxin produced by the fungi the Alternaria alternate genus, onto polycrystalline gold electrodes modified by a self-assembled monolayer (SAM) of 1-dodecanethiol (DDT) from unstirred solutions of the pure commercial reagent in 20% acetone (Ac) + 80% pH 7 phosphate buffer solutions (PBS) has been studied by cyclic (CV) and square wave voltammetries (SWV). The influence of different experimental conditions on the adsorptive process has been analyzed. The specific interaction of ATX-I with these modified gold electrodes was adequately described by a Freundlich adsorption isotherm. Electrochemical impedance spectroscopy (EIS) measurements were used to assess the state of the adsorbed thiol molecules, demonstrating that optimum conditions for analytical detection require the presence of defects in the monolayer, where analyte accumulation and charge transfer rate are enhanced with respect to well ordered monolayers. SWV was employed to generate the calibration curves. For a signal-to-noise ratio of 3: 1, a detection limit of 4 x 10(-8) mol dm(-3) (14 ppb) was calculated at a frequency (f) of 40 Hz. (c) 2007 Elsevier B.V. All rights reserved.