Generator-collector electroanalysis approaching the nanomolar level is demonstrated for the reduction of Ru(NH3)(6)(3+) in aqueous (NH4)(2)SO4 (saturated, as a naturally low-oxygen electrolyte medium) and at tin-doped indium oxide (ITO) electrodes. ITO-ITO double band and double plate geometries are compared. Cyclic voltammetric detection down into the sub-micromolar concentration level is readily achieved at co-planar ITO-ITO double plate junction electrodes with typically 4 mu m inter-electrode gap, 5 mm length, and ca. 62 mu m average inter-electrode trench depth. Trace oxygen (ca. 60 mu M) is shown to enhance both generator and collector currents and the cathodic excess current vertical bar I-generator vertical bar -vertical bar I-collector vertical bar is employed to estimate the bimolecular rate constant for Ru(NH3)(6)(2+) reacting with O-2, k(2) = 10(4) mol(-1) dm(3) s(-1). (C) 2012 Elsevier Ltd. All rights reserved.