Electrochemiluminescence Enhanced by a Non-Emissive Dual Redox Mediator

A sulfonated tris(1-phenylpyrazolato)iridium(III) complex ([Ir(sppz)₃]^3-) serves as a proof-of-concept non-emissive enhancer of the widely used ECL detection system of tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)₃]²⁺) with tri-n-propylamine (TPrA) co-reactant, acting through electrocatalysis of TPrA oxidation and efficient chemi-excitation of the luminophore. Using self-interference ECL spectroscopy, we show that the enhancer extends diffusion of the required electrogenerated precursors from the electrode surface. Previously reported enhancement through these pathways has been confounded by the inherent ECL of the enhancer, but the increase in [Ru(bpy)₃]²⁺ ECL intensity using [Ir(sppz)₃]^3- was obtained without its concomitant emission. The most prominent enhancement (11-fold) occurred at low potentials associated with the 'indirect' co-reactant ECL pathway, which translated to between 2- and 6-fold enhancement when the luminophore was immobilised on microbeads as a general model for enhanced ECL assays.