Although many electrogenerated chemiluminescence (ECL) co-reactants, such as tripropylamine (TPA) and oxalic acid, have been applied in Tris(bipyridine)ruthenium(II)/silica nanoparticles (Ru(bpy)32+/silica nanoparticles, RuS NPs) ECL system, the poor diffusion behavior of these co-reactants in silica matrix as well as its toxic disadvantages limited their further ECL analytical application. Therefore, it was very meaningful to explore a new type of co-reactant in RuS NPs ECL system for obtaining a good analytical result. In this paper, we found that the electrochemical oxidation reaction of H2O could be catalyzed by Cu(Tris)42+ (Tris(hydroxymethyl)aminomethane, Tris) complexes and produce the intermediate (·OH). The ECL of Ru(bpy)32+-doped RuS NPs could be induced by ·OH and produce the strong ECL signals. The possible ECL mechanism was investigated by ultraviolet-visible (UV-vis) absorption spectrum, electrochemical methods and ECL methods. It may be that when Cu2+ was added into the Tris-HCl solution, it would combine with the amino of Tris to form Cu(Tris)42+ complexes; in the subsequent ECL reaction process, Ru(bpy)32+ inside RuS NPs near by the surface of electrode was firstly oxidized to Ru(bpy)33+. At the same time, the reduction reaction of Ru(bpy)33+ would catalyze the oxidization of Cu(Tris)42+to generate the Cu(Tris)43+; then, the reduction of Cu(Tris)43+ would catalyze the electrochemical oxidation reaction of H2O and was accompanied by the generation of O2 and strong reducing agents (·OH). On the one hand, the silica substrate could protect Ru(bpy)32+-doped RuS NPs from O2 interference, and avoid the quenching effect of Ru(bpy)32+ ECL induced by O2. On the other hand, ·OH can rapidly go through the silica substrate and react with the oxidation state of Ru(bpy)33+ inside of RuS NPs because it is a kind of neutral group. Based on these findings, we develop a new ECL method for sensitive detection of Cu2+ using H2O molecular as a co-reacant. Under the optimal conditions, the proposed method achieved a detection limit of 1.0×10-7 mol/L with RSD of less than 5.0%.
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