Synthetic Melanin Coated Carbon Fiber Micro-Electrodes for Selective Detection of Peroxynitrite

Abstract

Melanin is a natural pigment produced by melanocytes and has many physiological functions. Recent studies have suggested that melanin can behave like a free radical scavenging antioxidant. In biological systems, free radicals can damage a wide array of the essential components in the human body, such as cells/tissues, DNA, proteins, and lipids. Peroxynitrite (PON) has emerged as a combination of two free radicals and it can yield secondary free radicals per homolytic decomposition. PON is a biological oxidant that has been linked with oxidative damage and disruption of redox control systems. The short lifespan and fast reactivity of PON add more challenge to measure its concentration under physiologic conditions.Carbon fiber electrodes (CFEs) have the advantage of providing a minimally invasive and a non-toxic platform when compared to other metal-based electrodes. In this research study, synthetic melanin-coated CFEs were prepared using electro-deposition of 5,6-dihydroxyindole monomer. Surface characterizations including scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were utilized to confirm the melanin deposition and to examine the morphological differences between the modified CFEs before and after exposure to PON. Cyclic voltammetry, differential pulse voltammetry, and amperometry were used to test the performance of CFEs modified with synthetic melanin in terms of detection and quantification of PON. Our preliminary findings have shown that synthetic melanin modified CFEs have greater sensitivity when compared to glassy carbon electrodes and other macro-electrodes. In addition, melanin-coated CFEs exhibit high selectivity when they tested for PON detection in the presence of biological interferents. The present results indicate the possibility of using melanin-coated CFEs as a sensitive and selective sensing platforms for peroxynitrite detection in the nanomolar range at physiologic conditions.