Finite Element Simulation of the Coreactant Electrogenerated Chemiluminescence Mechanism

Electrogenerated chemiluminescence (ECL) is an electron transfer between redox products formed at an electrode that results in the formation of an excited state species, which is capable of photon emission. This excited state can be achieved by a reaction between an oxidized and a reduced form of the same luminophore, or via the reaction of the oxidised or reduced luminophore with an electrochemically generated co-reactant. This is of great interest to the biosensing community, as the attachment of multiple ECL-active luminophores to a target molecule is a very attractive signal amplification strategy. This is a complicated process involving multiple reaction steps, and so a thorough understanding of the complete reaction process and the evolution of the excited state luminophore is essential. In order to gain a greater understanding of the ECL mechanism, we use finite element digital simulations to explicitly model each reaction step. This was done for an organometallic ECL standard, tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)3 2+), and tripropylamine (TPA), where the simultaneous oxidation of Ru(bpy)3 2+ and TPA result in the generation of the excited state Ru(bpy)3 2+*. The geometry and reaction conditions were chosen to match experimental data from our previously developed cuvette based system. Comparison of simulated voltammetry and ECL emission both agreed well with the experimental data, validating the experimental results and also giving insight into the impact of the confined cuvette geometry on the observed voltammetry. Investigations into the simulated concentration profiles also revealed the ECL emission to be confined close to the electrode surface, and so the impact of side reactions at the counter electrode could be omitted. Importantly, each step in the ECL process could be individually analysed and quantified in order to provide a greater understanding of the mechanism as a whole. Figure 1: A) Simulated concentration of the excited state luminophore Ru(bpy)3 2+* at the position of peak ECL emission. B) Comparison of the experimental ECL emission peak with the simulated concentration of Ru(bpy)3 2+*, showing good agreement. Figure 1