Peroxynitrite (PON, ONOO−) is a powerful oxidizing agent generated in vivo by the diffusion-controlled reaction of nitric oxide (^·NO) and superoxide (O₂^·−) radicals. Peroxynitrite levels accumulate under oxidative stress. Elevated peroxynitrite levels are associated with chronic inflammatory disorders including neurological and vascular diseases, as well as a number of other pathophysiological conditions. The accurate detection of this analyte in biological systems is of paramount importance, not only to understand the genesis and causes of ailment at the tissue/cellular level, but also to suggest and design potential therapeutic routes.

In the past, we studied the sensitivity of carbon electrodes modified by polymerized hemin (iron protoporphyrin) as standalone and in combination with conductive polymer PEDOT (3,4-ethylendioxythiophene). These polymerized surfaces have been used as platforms for amperometric measurements of peroxynitrite both in still solutions and under flow conditions. More recently, we extended this line of research to the use of hemin functionalized graphene as a catalytic platform for PON oxidative detection.

In this work we explored and discussed the sensitivity of manganese-based interfaces for peroxynitrite amperometric determination. Surfaces of electrodeposited manganese (Mn), manganese-graphene, and manganese-decorated graphene/hemin-based nanostructures were formed on glassy carbon electrodes as well as on carbon fiber microelectrodes. The effect of graphene on the electrodeposition of Mn was investigated by cyclic voltammetry. We tested these interfaces for electro-catalytic sensing of peroxynitrite in solution using chronoamperometric technique. The morphology of the prepared manganese interfaces was characterized using scanning electron microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA), Ultra-Violet/Visible (UV/Vis), X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. The results showed that manganese-functionalized hemin/graphene enhances peroxynitrite detection and quantification compared to hemin/graphene-only interfaces. We noticed that there is a synergistic effect of the presence of graphene with manganese nanoparticles in the prepared materials. We compared and contrasted on how graphene nano-sheets affect the electrochemical behavior of hemin-modified electrodes in the absence and presence of manganese nanoparticles. In conclusion, we found that the incorporation of manganese influences the sensitivity of PON-sensing hemin/graphene platforms.