A nano-ordered topographical surface (0.8-1.6 mn) was prepared by the modification of gold nano-particles on an evaporated An film. Nano-ordered topographical effects for the protonation-deprotonation behaviors of 10-carboxy-l-decanethiol (CDT) monolayers adsorbed onto a gold surface were then demonstrated by the use of [Ru(NH3)(6)](3+) as a redox probe. On the assumption that current of [Ru(NH3)(6)](3+) on the CDT modified electrode is composed to two independent parts of the protonated and deprotonated CDT, the titration curve for the redox peak current values obtained from cyclic voltammograms of [Ru(NH3)(6)](3+) as a function of pH was analyzed by a statistical mechanical model for water-solid interfaces (1-pKa model). The results obtained strongly suggest that the electrostatic repulsion of the carboxylic acid terminated self-assembled monolayer adsorbed onto a gold surface with nano-ordered topography was much smaller than that adsorbed on an atomically flat gold surface, which was also supported by reflection FTIR measurements. (C) 2007 Elsevier B.V. All rights reserved.