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

The electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) molecule which is immobilized on Nafion coated nanoporous gold electrode (Ru(bpy)(3)(2+)/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)(3)(2+) molecule immobilized on Nafion coated polycrystalline gold (Ru(bpy)(3)(2+)/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)(3)(2+)/Nafion/NPG when compared with Ru(bpy)(3)(2+)/Nafion/pc-Au in PBS (pH 7.4). Interestingly, this kind of ECL signal is not observed in the case of Ru(bpy)(3)(2+) 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)(3)(2+)/Nafion/NPG. Upon electrochemical oxidation on Ru(bpy) (2+)(3)/Nafion/NPG at higher potential, the stored Ru(bpy)(3)(2+) is converted into Ru(bpy)(3)(3+) at the same time generated reactive intermediate species like OH radical from the conversion of Au(OH)(3) to Au-0 during the reduction process leads energetic electron transfer reaction to proceed the excited state of Ru(bpy)(3)(2+) 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. (C) 2020 Elsevier Ltd. All rights reserved.