The electrochemical detection of nitric oxide (NO center dot) and peroxynitrite anion (ONOO-) was investigated at Pt-black electrodes in microchannels. Owing to the high reactivity of these species under conditions close to physiological media, kinetic parameters were determined before evaluating the detection performances from synthetic solutions. Highly sensitive and stable Pt-black electrodes allowed detection limits down to 30 nM (NO center dot) and 40 nM (ONOO-) to be reached with very high sensitivities. As NO center dot and ONOO- are two relevant biological molecules involved in oxidative stress their simultaneous detections with other major molecules like hydrogen peroxide and nitrite were also performed and validated experimentally at pH 8.4. These results demonstrated that relative ROS/RNS contents in synthetic mixtures can be easily assessed at selected detection potentials. Beyond the interest of using small volumes in microfluidic channels, optimization of detection requires precise conditions easy to implement. These were delineated to lead in microdevices to high-performances detection of oxidative stress metabolites either from analytes or from the production of a few living cells like macrophages. (C) 2014 Elsevier Ltd. All rights reserved.