The disclosure relates to electrodes and related sensor apparatus for the detection of nitric oxide (NO) and/or peroxynitrite (PON). The electrodes and sensors incorporate electrically conducting boron-doped diamond (BDD) to provide a selective and quantitative detection platform. The sensing electrode for detection of NO includes metallic nanoparticles for oxidation of NO as well as anionic polyelectrolyte layer over the electrically conducting BDD layer. The sensing electrode for detection of PON includes an electrically conductive polymeric layer including a metal-complexed porphyrin for redox reaction with PON over the electrically conducting BDD layer. A corresponding sensor apparatus includes one or two electrochemical cells with associated electrolytes, separate working electrodes for the separate, selective detection of NO or PON, and associated reference electrode(s) and counter electrode(s). Use of the related sensor with various electrochemical techniques to detect NO and/or PON in exhaled breath can be used for detection and/or diagnosis of lung-related conditions.
