Peroxynitrite Sensing: From Graphene-Based Platforms to Modified Boron-Doped Diamond Electrodes

Peroxynitrite (PON) is a major cytotoxic agent, implicated in a host of pathophysiological conditions. In biological systems, peroxynitrite is the primary product of the reaction of superoxide ion and nitric oxide, and has been lately at the forefront of investigations dealing with nitroxidative stress. One major challenge in the analytical determination of peroxynitrite under physiologic conditions is its short half-life and its fast reactivity with many cellular targets.  Spectroscopic and other detection methods for peroxynitrite have been proposed but face the problem of real-time quantification and particularly when localized measurements are needed.  We have shown that catalyzed electrochemical detection of peroxynitrite is a simpler and more convenient technique. In the past, we described the use of polymerized hemin (iron protoporphyrin IX) and other porphyrins on graphite electrodes as platforms for amperometric measurement of peroxynitrite both in still solutions and under flow conditions. This work has been extended to reduced graphene oxide functionalized with hemin as a catalytic platform for PON oxidative detection. Boron-doped diamond electrodes (BDD) have been used as platforms for electrochemical detection of a number of analytes in environmental samples as well as in biological media. BDD electrodes have the advantage to provide a relatively wide electrochemical window as well as low capacitive currents. In the present paper we compare and contrast the direct electrochemical oxidation of peroxynitrite on BDD and the catalytic oxidation of PON on modified diamond electrodes as potential sensing platforms of PON. Boron-doped diamond based microarray electrodes have been proposed as potential devices for neuronal stimulation. We hypothesize that PON generated at the array-tissue interface is a major cytotoxic intermediate leading to ultimate tissue death. Developing sensing electrodes based on catalytic detection of PON on boron-doped diamond electrodes is a step towards using individually addressable electrodes in a BDD electrode array for both electrical stimulation and monitoring of PON levels as a predictor of tissue deterioration and, ultimately, death. Understanding the fundamental processes involved during the catalytic oxidation of PON on modified BDD offers the possibility to fine-tune the surface to optimize PON detection.