Electrochemiluminescence Enhanced by a Non-Emissive Dual Redox Mediator

Area of Science:

• Analytical Chemistry
• Electrochemistry
• Luminescence

Background:

• Tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)₃]²⁺) is a widely used luminophore in electrochemiluminescence (ECL) detection.
• Enhancement of ECL signals is crucial for improving assay sensitivity.
• Previous enhancers often suffer from inherent emission, confounding results.

Purpose of the Study:

• To introduce a non-emissive enhancer for ECL detection.
• To investigate the mechanism of enhancement by a sulfonated iridium complex.
• To demonstrate improved ECL intensity without enhancer-derived emission.

Main Methods:

• Synthesis and characterization of a sulfonated tris(1-phenylpyrazolato)iridium(III) complex ([Ir(sppz)₃]^3-).
• Electrochemical analysis using self-interference ECL spectroscopy.
• Evaluation of ECL enhancement with [Ru(bpy)₃]²⁺ and tri-n-propylamine (TPrA).
• Testing the enhancer in a model system with immobilized luminophore on microbeads.

Main Results:

• [Ir(sppz)₃]^3- acts as a non-emissive enhancer for [Ru(bpy)₃]²⁺/TPrA ECL system.
• Enhancement mechanism involves electrocatalysis of TPrA oxidation and efficient chemi-excitation.
• Self-interference ECL spectroscopy confirmed extended diffusion of electrogenerated precursors.
• Up to 11-fold ECL enhancement observed at low potentials without concomitant emission from the enhancer.
• 2- to 6-fold enhancement achieved with immobilized luminophore on microbeads.

Conclusions:

• Sulfonated iridium complexes can serve as effective non-emissive ECL enhancers.
• The proposed mechanism clarifies previous ambiguities regarding enhancer-derived emission.
• This approach offers a viable strategy for boosting ECL assay performance and sensitivity.