Peroxynitrite is a very reactive and cytotoxic species that plays important pathophysiological roles, particularly in the brain. It is also suspected to be a factor involved in tissue damage that results from long term deep brain neural stimulation. Accurate determination of peroxynitrite concentration is inherently difficult due to its high reactivity and concentration range. Various methods for peroxynitrite determination have been reported including indirect spectroscopic assays and, recently, direct electrochemical methods. Currently, this field is still actively growing in the pursuit of viable electrochemical probes or catalytic materials as interfaces for efficient peroxynitrite detection. A durable and reliable electrochemical sensor would be valuable in order to monitor peroxynitrite generation near sites of electrical neurostimulation.In this work, we prepared and characterized a functional thin film material based on an organic selenide on graphite electrodes and used the interface in sensitive electrochemical determination of peroxynitrite. First, we describe the preparation and grafting of the catalytic material based on the electrodeposition of organic selenides on graphite electrodes. Next, we report on the characterization of the resulting grafted film material on graphite interface using various physicochemical methods including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS). We then tested the performance of resulting aniline selenide catalytic material on modified electrodes as peroxynitrite sensing interfaces using voltammetry and dose-response amperometry. The grafted thin film material showed a significant enhancement in peroxynitrite oxidative current compared to electrodes with aniline only (i.e. materials devoid of selenium) under the same conditions. In the presentation we will show that the enhancement in peroxynitrite signal is the result of an electrocatalytic mechanism where the grafted selenide-based organic material at the oxidized state mediates the electrocatalytic oxidation of peroxynitrite. In terms of selectivity, the electrocatalytic detection of PON on electrodes modified with the selenide compound responds better and selectively toward PON as a target analyte over other potentially interfering analytes such as nitric oxide, nitrite, and nitrate. To the best of our knowledge, this is the first time a selenium-based organic material electrochemically grafted at an electrode surface is used for catalytic detection and quantification of peroxynitrite.