Sara Knežević, Emily Kerr, Giovanni Valenti, Francesco Paolucci, Paul S. Francis, Conor F. Hogan, Neso Sojic, Frédéric Kanoufi

Electrochimica Acta, 499, 2024, 144677

Electrochemiluminescence (ECL) has emerged as a sensitive analytical technique with a wide range of applications. While recent studies have begun to explore the role of redox mediators to facilitate ECL systems, this work extends these foundational insights by developing a comprehensive theoretical framework that supports, generalizes, and rationalizes mechanistic pathways borrowed from molecular electrocatalysis. This advancement is demonstrated through the electrocatalytic amplification of coreactant ECL within the [Ru(bpy)3]2+/TPrA system, utilizing a water-soluble redox-active Ir(III) complex as an electrocatalyst. Our investigation unveils previously uncharted mechanisms that enable the enhancement of Ru complex ECL at low electrode potentials, crucially without requiring the direct oxidation of [Ru(bpy)3]2+ or TPrA at the electrode, thus offering a deeper understanding of ECL activation through moelcular electrocatalysis. Through an integrated approach combining electrochemical analysis, spectroscopic investigation, and finite element modeling, we elucidate how the redox mediator critically modulates ECL efficiency by controlling the kinetics of radical species production and decay. The mediation by the Ir(III) complex not only governs the generation of TPrA radicals and excited [Ru(bpy)3]2+ states, thereby enhancing ECL intensity, but also the conditions under which ECL can be quenched. Further exploration of the mediator's redox characteristics provides predictive insights into ECL behavior, underscoring the mediator's redox potential as pivotal in determining ECL onset, peak potential, and intensity. This refined understanding paves the way for tailoring ECL systems for enhanced performance in analytical, imaging, and biomedical applications through the judicious selection of redox mediators.

Leslie R. Arias-Aranda, Gerardo Salinas, Alexander Kuhn, Guobao Xu, Frédéric Kanoufi, Laurent Bouffier, Neso Sojic

Chem. Sci., 2024,15, 8723-8730

Electrochemiluminescence (ECL) is a powerful analytical approach that enables the optical readout of electrochemical processes. Over the last few years, ECL has gained considerable attention due to its large number of applications, including chemical sensing, bioanalysis and microscopy. In these fields, the promotion of ECL at bipolar electrodes has offered unprecedented opportunities thanks to wireless electrochemical addressing. Herein, we take advantage of the synergy between ECL and bipolar electrochemistry (BE) for imaging light-emitting layers shaped by hydrodynamics, polarization effects and the nature of the electrochemical reactions taking place wirelessly on a rotating bipolar electrode. The proof-of-principle is established with the model ECL system [Ru(bpy)3]2+/tri-n-propylamine. Interestingly, the ECL-emitting region moves and expands progressively from the anodic bipolar pole to the cathodic one where ECL reactants should neither be generated nor ECL be observed. Therefore, it shows a completely unusual behavior in the ECL field since the region where ECL reagents are oxidized does not coincide with the zone where ECL light is emitted. In addition, the ECL patterns change progressively to an “ECL croissant” and then to a complete ring shape due to the hydrodynamic convection. Such an approach allows the visualization of complex light-emitting patterns, whose shape is directly controlled by the rotation speed, chemical reactivity and BE-induced polarization. Indeed, the bipolar electrochemical addressing of the electrode breaks the circular symmetry of the reported rotating system. This unexplored and a priori simple configuration yields unique ECL behavior and raises new curious questions from the theoretical and experimental points of view in analytical chemistry. Finally, this novel wireless approach will be useful for the development of original ECL systems for analytical chemistry, studies of electrochemical reactivity, coupling microfluidics with ECL and imaging.

Dongni Han, Mi Yang, Zengyu Feng, Yulian Wu, Neso Sojic, Dechen Jiang

ACS Appl. Mater. Interfaces 2024, 16, 25, 32078–32086

The traditional recognition of extracellular matrix (ECM) at tissue sections relies on the time-consuming immunofluorescence that could not meet the demand of rapid diagnosis. Herein, we introduce a thickness-resolved electrochemiluminescence (ECL) microscopy to image thin-layer ECM at tissue sections for fast histopathological analysis. The unique surface-confined ECL mechanism enables to unveil the diversity and complexity of multiple tissue structures with varying thicknesses. Notably, the short lifetimes and the limited diffusion of electrogenerated coreactant radicals combined with their chemical reactivity result in a 2-fold increase in ECL intensity on ECM structures compared to the remaining tissue, enabling ECM visualization without specific labeling. The further quantitation of the ECM localization within tissue sections furnishes crucial insights into tumor progression and, more importantly, differentiates carcinoma and paracancerous tissues from patients in less than 30 min. Moreover, the reported electrochemistry-based microscopy is a dynamic approach allowing to investigate the transport, tortuosity, and trafficking properties through the tissues. This thickness-resolved recognition strategy not only opens new avenues for imaging complex samples but also holds promise for expediting tissue pathologic diagnosis, offering a more automated protocol with enhanced quantitative data compared to current intraoperative pathology methods.

Sara Knežević, Dongni Han, Baohong Liu, Dechen Jiang, Neso Sojic

https://doi.org/10.1002/anie.202407588

The orthogonality of the electrochemical trigger and the optical readout distinguishes electrochemiluminescence (ECL) from classic microscopy and electrochemical techniques. In this review, we summarize the recent advances in ECL microscopy, emphasizing original configurations which enable the mapping of the (electro)chemical reactivity and the imaging of biological entities. Finally, we highlight the recent achievements in imaging single ECL photons or molecules.