Unraveling the reaction mechanism of co-reactant free in-situ cathodic solid state ECL of Ru(bpy)32+ molecule immobilized on Nafion coated nanoporous gold electrode

• DOI: 10.1016/j.electacta.2020.136920
• Publication Date: 2020-08-12T08:45:22Z
• Authors: Chikkili Venkates...; Mathavan Sornambigai; Shanmugam Senthil...
• Keywords: Nafion; Nanoporous; Electrochemiluminescence; Glassy carbon

Abstract The electrochemiluminescence (ECL) of Ru(bpy)32+ molecule which is immobilized on Nafion coated nanoporous gold electrode (Ru(bpy)32+/Nafion/NPG) is investigated without involving any additional co-reactant in 0.1 M phosphate buffer solution (PBS) at pH 7.4 and the observed results are compared with Ru(bpy)32+ molecule immobilized on Nafion coated polycrystalline gold (Ru(bpy)32+/Nafion/pc-Au). Because of high surface area volume ratio and more active sites on NPG, the obtained co-reactant free unusual cathodic ECL signal at less cathodic potentials (0.1 V vs Ag/AgCl) showed 40 times higher intensity on Ru(bpy)32+/Nafion/NPG when compared with Ru(bpy)32+/Nafion/pc-Au in PBS (pH 7.4). Interestingly, this kind of ECL signal is not observed in the case of Ru(bpy)32+ molecule which is immobilized on Nafion coated glassy carbon (GC) and polycrystalline platinum (pc-Pt) electrodes. Based on the detailed experiments on effect of different pH, various direction of scanning potential and in-situ spectroelectrochemical studies, we proposed a new reaction mechanism for the unusual cathodic ECL on Ru(bpy)32+/Nafion/NPG. Upon electrochemical oxidation on Ru(bpy)32+/Nafion/NPG at higher potential, the stored Ru(bpy)32+ is converted into Ru(bpy)33+ at the same time generated reactive intermediate species like OH radical from the conversion of Au(OH)3 to Au0 during the reduction process leads energetic electron transfer reaction to proceed the excited state of Ru(bpy)32+ and then emits light. Unlike the conventional ECL system, this kind of co-reactant free in-situ generated solid state ECL approach offers to the scope in various bio analytical applications.