Tailoring nanostructured sensing electrode materials to high antifouling resistance has been one of the main priorities of the development of water quality sensors in the 21st century. Nanostructured Cu0.4Ru3.4O7 + RuO2-SEs have been developed to address the bio-fouling problem. The change in Cu0.4Ru3.4O7 + RuO2 structural development being promoted by advances in nano- and micro-scale pattering. Nanostructured Cu0.4Ru3.4O7 + RuO2-SEs with different mol% of Cu2O were screen-printed on alumina sensor substrates and were consequently subjected to a 3-month field trial at the Water Treatment Plant. Their structural and electrochemical properties before and after the experiment were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical cyclic voltammerty (CV) techniques. The relationship between dissolved oxygen (DO) and the sensor's potential difference was found to be relatively linear, with the maximum sensitivity of -46 mV per decade being achieved at 20 mol% Cu2O at 7.27 pH. Moreover, a 3-month field trial in the sewerage environment has shown that Cu0.4Ru3.4O7 + RuO2-SE with 20 mol% of Cu2O possesses much higher defences against bio-fouling than the same SE with only 10 mol% of Cu2O. The super-hydrophobic property of the developed Cu0.4Ru3.4O7 + RuO2 complex oxide has been considered as one of the essential pre-requisites for high antifouling resistance. Multiple antifouling defence strategies from biomimetic to bio-inspired must be incorporated in further development of nanostructured oxide SE to solve problems of bio-fouling on the sensor's SE. (C) 2011 Elsevier Ltd. All rights reserved.