Electrochemical oxidation of guanine mediated by [Ru(bpy)(2)dpp](2+) (where bpy=2,2'-bipyridine, dpp=2,3-bis (2-pyridyl) pyrazine) and their electrochemical assembly at an ITO electrode prompted by guanine have been investigated with cyclic voltammetry and differential pulse voltammetry. It is found that [Ru(bpy)(2)dpp](2+) can serve as an excellent mediator to induce the oxidation of guanine, and the mediated peak currents increase linearly with the rise of guanine concentration in the range from 0.01 to 0.20 mmol L-1. Interestingly, with the increase of repetitive voltammetric sweeping numbers, [Ru(bpy)(2)dpp](3+/2+) can be assembled onto the ITO electrode and guanine has the ability to enhance the peak currents of prewaves. Also, with the rise of guanine concentration from 0.01 to 0.15 mmol L-1, the peak currents of prewaves increase gradually. Meanwhile, the mediated mechanism of guanine oxidation by [Ru(bpy)(2)dpp](2+) and the assembled process of [Ru(bpy)(2)dpp](3+/2+) on the ITO surface in the presence of guanine are discussed in detail. (C) 2008 Elsevier Ltd. All rights reserved.