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%.

Key words: electrogenerated chemiluminescence, Tris(bipyridine)ruthenium(II), Tris(bipyridine)ruthenium(II)/silica nanoparticles, Cu²⁺