We report here the proof of concept of the use of new assembled arrays of ultramicroelectrodes (UMEs) for the simultaneous and dynamic sensing of reactive nitrogen species such as nitric oxide (NO) and peroxynitrite (ONOO-, so-called PUN) released by cultured cells. These devices fill the need to study the key roles of these two reactive nitrogen species where a chemical imbalance is implicated in several pathologies and physiological disorders. Arrays containing over 2400 gold UMES were designed in such a way to increase sensitivity and allow detection of low concentrations of the target analytes in vivo. These disposable platforms are then integrated within cell culture wells and plates, resulting in an easy-to-handle tool for cellular biology. They were successfully used to detect in real time PUN formed in situ upon the reaction of NO released from a NO donor molecule ((Z)-1-[N-(2-aminoepropyl)-N-(2-ammoniopropyl)amino]-diazen-1-ium-1,2-diolate) and superoxide (O-2(-)) released by PMA (phorbol-12-myristate-13-acetate)-induced HL60 cells. (C) 2014 Elsevier Ltd. All rights reserved.