publication

New paper in Angewandte Chemie International Edition

Autocatalytic Electrochemiluminescence

Claudia Martinez Asenjo, Francesco Petrini, Alessandro Fracassa, Dr Sara Knežević, Elisa D’Arrigo, Prof. Paul S. Francis, Prof. Francesco Paolucci, Prof. Neso Sojic, Dr Frédéric Kanoufi, Prof. Giovanni Valenti

Published in Angewandte Chemie International Edition

 

Abstract
Electrochemiluminescence (ECL) is a powerful analytical technique that generates light through electrochemically induced reactions, enabling ultrasensitive biosensing and imaging of submicrometric objects. Conventional ECL systems, such as those using Ru(bpy)32⁺ and tri-n-propylamine (TPrA), require high applied potentials (oxidation at ∼1.4 V versus Ag/AgCl), leading to electrode surface modification and parasitic reactions. Herein, we present a novel autocatalytic ECL mechanism that drastically lowers the triggering potential to −0.2 V by exploiting the synergistic interplay between oxalate (C2O42−) and peroxydisulfate (S2O82−) radicals, mediated by Ru(NH3)63+ reduction. This system generates ECL without direct oxidation of the luminophore, but instead through a mild reduction process, relying on homogeneous radical reactions (SO4•− and CO2•−) to populate the Ru(bpy)32⁺* excited state. Experimental investigation at different Ru(NH3)63+/S2O82−/C2O42− concentration ratios, backed by finite element simulations, demonstrates the autocatalytic cycle’s capability of exciting luminophores with a bandgap as high as 2.77 eV (blue-emitting Ir(III) complex), while also showing a more stable ECL emission and achieving an emitting layer as thick as ∼4.8 ± 0.2 µm. These findings establish a low-potential ECL pathway with a large emitting layer, extending the applicability of such nontoxic coreactants—historically limited by their short-lived radicals—and potentially paving the way for new frontiers in ECL.

Graphical abstract

The presented autocatalytic cycle, mediated by the reduction of Ru(NH3)63+ and arising from the synergistic interplay between oxalate (C2O42−) and peroxydisulfate (S2O82−) via their radical intermediates, prompts ECL emission from Ru(bpy)32+ at potentials as low as -0.2 V versus Ag/AgCl. This system generates ECL without direct oxidation of the luminophore, but instead through a cascade of redox-mediated electron transfers triggered by the mild reduction of Ru(NH3)63+.

Autocatalytic Electrochemiluminescence

Claudia Martinez Asenjo, Francesco Petrini, Alessandro Fracassa, Dr Sara Knežević, Elisa D’Arrigo, Prof. Paul S. Francis, Prof. Francesco Paolucci, Prof. Neso Sojic, Dr Frédéric Kanoufi, Prof. Giovanni Valenti

Published in Angewandte Chemie International Edition

 

Abstract
Electrochemiluminescence (ECL) is a powerful analytical technique that generates light through electrochemically induced reactions, enabling ultrasensitive biosensing and imaging of submicrometric objects. Conventional ECL systems, such as those using Ru(bpy)32⁺ and tri-n-propylamine (TPrA), require high applied potentials (oxidation at ∼1.4 V versus Ag/AgCl), leading to electrode surface modification and parasitic reactions. Herein, we present a novel autocatalytic ECL mechanism that drastically lowers the triggering potential to −0.2 V by exploiting the synergistic interplay between oxalate (C2O42−) and peroxydisulfate (S2O82−) radicals, mediated by Ru(NH3)63+ reduction. This system generates ECL without direct oxidation of the luminophore, but instead through a mild reduction process, relying on homogeneous radical reactions (SO4•− and CO2•−) to populate the Ru(bpy)32⁺* excited state. Experimental investigation at different Ru(NH3)63+/S2O82−/C2O42− concentration ratios, backed by finite element simulations, demonstrates the autocatalytic cycle’s capability of exciting luminophores with a bandgap as high as 2.77 eV (blue-emitting Ir(III) complex), while also showing a more stable ECL emission and achieving an emitting layer as thick as ∼4.8 ± 0.2 µm. These findings establish a low-potential ECL pathway with a large emitting layer, extending the applicability of such nontoxic coreactants—historically limited by their short-lived radicals—and potentially paving the way for new frontiers in ECL.

Graphical abstract

The presented autocatalytic cycle, mediated by the reduction of Ru(NH3)63+ and arising from the synergistic interplay between oxalate (C2O42−) and peroxydisulfate (S2O82−) via their radical intermediates, prompts ECL emission from Ru(bpy)32+ at potentials as low as -0.2 V versus Ag/AgCl. This system generates ECL without direct oxidation of the luminophore, but instead through a cascade of redox-mediated electron transfers triggered by the mild reduction of Ru(NH3)63+.

by ECLectic Project

New paper in Angewandte Chemie International Edition

Electrochemiluminescence Modulation by a Versatile Organic Redox Mediator

Miaoxia Liu, Xianjing Huang, Bertrand Goudeau, Chenying Wang, Neso Sojic, Haidong Li

Published in Angewandte Chemie International Edition

 

Abstract
Adding a redox-active iridium complex has emerged recently as a new mechanistic pathway to enhance electrochemiluminescence (ECL). But, these redox mediators are costly, require sophisticated synthesis, and induce concomitantly intense ECL emission or a strong background. Herein, we report the use of nortropine N-oxyl (NNO) radical as a non-emissive redox mediator for modulating the co-reactant ECL emission of the archetypical [Ru(bpy)3]2+ luminophore, thanks to its particular reactivity involving hydride transfer from amines. The reversible oxidation of NNO produced its oxoammonium cation and catalyzed the oxidation of tri-n-propylamine (TPrA) and 2-(dibutylamino)ethanol (DBAE) co-reactants. The electrocatalysis of NNO induced a significant decrease in the homogeneous solution-based ECL. However, it offered the versatility to amplify the heterogeneous ECL by 7.3-fold for TPrA or even up to 12.5-fold for DBAE in a bead-based immunosensing format, and by 5.4-fold on single cells. The electrocatalytic mechanism of NNO was further deciphered by the density functional theory (DFT) calculations. The background-free ECL modulation by NNO depends on either the depletion of amine radical or the generation of another alkoxyl radical at the electrode. Such dramatic ECL amplification opens new perspectives for improving the existing ECL bioassays and microscopy and the design of new biosensing schemes.

Graphical abstract

The electrocatalysis of NNO for the co-reatant oxidation enhances the heterogeneous ECL of [Ru(bpy)3]2+ on labeled microbeads or cells. This unique electrocatalytic oxidation of co-reactant makes NNO a versatile non-emissive redox mediator for ECL studies.

by ECLectic Project

New paper in Chemical & Biochemical Imaging

Gamma correction and color space transformations for quantitative analysis of electrochemiluminescence images using smartphone cameras

Stephania Rodríguez Muiña, Rajendra Kumar Reddy Gajjala, Eduardo Fernández Martín, and Francisco Javier del Campo

Published in Chemical & Biochemical Imaging

 

Abstract
Quantitative imaging of luminescent signals, ranging from electrochemiluminescence (ECL) and chemiluminescence to colorimetric assays, is increasingly performed using consumer-grade digital cameras and smartphones. However, device-dependent variability, nonlinear signal encoding, and the absence of standardized workflows hinder reproducibility and quantification accuracy. This work presents a generalized methodology for robust signal quantification in luminescent systems using digital imaging, with ECL as a model case. By combining synchronized electrochemical control, manual optimization of imaging parameters, gamma correction, and color space transformations, accurate device-independent analysis is enabled. Using Ru(bpy)32+/TPrA as a test system, we evaluate RGB, CIEXYZ, and CIELAB color spaces, identifying optimal channels for sensitivity and dynamic range. Our performance assessment underscores the importance of transfer function selection and supports both linear and nonlinear quantification models. Results show that linearized r and X color channels offer broad dynamic ranges with moderate sensitivity, while encoded R and a* channels provide higher sensitivity at low concentrations, requiring nonlinear modeling to extend their quantification range. This scalable approach enables standardized, high-throughput optical analysis using low-cost camera platforms, with broad applications in diagnostics, biosensing, and analytical chemistry.

by ECLectic Project

Abstract image for the publication

New paper in Chemical Communications

Overcoming kinetic barriers of remote electrochemiluminescence on boron-doped diamond via catalytic coreactant oxidation

Alessandro Fracassa, Chiara Mariani, Andrea Fiorani, Yasuaki Einaga, Conor F. Hogan, Francesco Paolucci, Neso Sojic, Paul S. Francis and Giovanni Valenti

Published in Chemical Communications

 

Abstract
The effectiveness of boron-doped diamond (BDD) as a platform for electrochemiluminescence (ECL) bead-based bioassays is hindered by the sluggish rate of heterogeneous tri-n-propylamine (TPrA) oxidation. To address this, we investigate the ECL of Ru(II)-coated microbeads in the presence of a redox mediator, exploring the effect of applied potential and electrode surface terminations. Using a redox mediator, the ECL signal on BDD is enhanced by up to 46-fold.

Abstract image for the publication "Overcoming kinetic barriers of remote electrochemiluminescence on boron-doped diamond via catalytic coreactant oxidation"

by ECLectic Project

Tunable electrochemiluminescence of TADF luminophores: manipulating efficiency and unveiling water-soluble emitters

New paper in Chemical Science

Tunable electrochemiluminescence of TADF luminophores: manipulating efficiency and unveiling water-soluble emitters

Alessandro Fracassa, Francesco Calogero, Giulio Pavan, Pavlos Nikolaou, Andrea Fermi, Paola Ceroni, Francesco Paolucci, Pier Giorgio Cozzi, Thomas Scattolin, Nicola Demitri, Fabrizia Negri, Andrea Gualandi, Alessandro Aliprandi and Giovanni Valenti

Published in Chemical Science

 

Abstract
Thermally Activated Delayed Fluorescent (TADF) luminophores offer the potential to achieve 100% Internal Quantum Efficiency (IQE) by harvesting both singlet and triplet excitons via reverse intersystem crossing from T1 to S1. This class of molecules has therefore been embraced in the pursuit of cheaper and more efficient electrochemiluminescent (ECL) labels. The present study explores how tuning the electron-donating (D) and -accepting (A) strengths of peripheral substituents affects the ECL emission of mono- and dicyanoarene-based TADF dyes. To this end, we synthesized two series of TADF compounds, independently manipulating electron donors and acceptors by (i) halogenating electron-rich diphenylamine moieties, or (ii) mono- or di-substituting the electron-poor cyanoarene core with either fluorine or imidazole. Through a comparative analysis, we elucidate the role of each substituent in shaping the photophysics of the investigated luminophores. Despite only achieving a relative ΦECL as high as 1.27%, this framework identifies several molecular features that boost the ECL efficiency to pave the way for designing highly efficient TADF-based ECL emitters. Ultimately, imidazole substituents are exploited as a platform for functionalization with triethylene glycol units. The resulting water-soluble TADF luminophores are characterized under conditions usual to commercial ECL bioanalysis, proving their potential as a cost-effective alternative replacement to [Ru(bpy)3]2+ in clinical diagnostic.
Tunable electrochemiluminescence of TADF luminophores: manipulating efficiency and unveiling water-soluble emitters
Fig. 1 Molecular structures of three different scaffolds, namely 3DPABN, 3DPAIPN, and 4DPAIPN. The first two molecular platforms underwent further modification by derivatizing the cyanoarene accepting core with fluorine atoms (i.e., 3DPA2FBN and 3DPAFIPN), imidazole heterocycles (i.e., 3DPA2ImBN and 3DPAImIPN), or imidazole units bearing a triethylene glycol chain to provide water solubility (i.e., [3DPA2(ImTEG)BN](OTs)2 and [3DPA(ImTEG)IPN]OTs). On the other hand, the functionalization of 4DPAIPN focused on derivatizing the electron-donating DPA groups, which were subjected to mono- or bi-insertion of bromine or chlorine atoms (i.e., 4(BrDPA)IPN, 4(Br2DPA)IPN and 4(Cl2DPA)IPN).

by ECLectic Project

AnalBioChem_sept24_FrontespizioNews

New paper in Analytical and Bioanalytical Chemistry

Biosensing strategies using recombinant luminescent proteins and their use for food and environmental analysis

Fernando Pradanas-González, Marta García Cortés, Bettina Glahn-Martínez, Melisa del Barrio, Pablo Purohit, Elena Benito-Peña and Guillermo Orellana

New paper in Analytical and Bioanalytical Chemistry

Abstract

Progress in synthetic biology and nanotechnology plays at present a major role in the fabrication of sophisticated and miniaturized analytical devices that provide the means to tackle the need for new tools and methods for environmental and food safety. Significant research efforts have led to biosensing experiments experiencing a remarkable growth with the development and application of recombinant luminescent proteins (RLPs) being at the core of this boost. Integrating RLPs into biosensors has resulted in highly versatile detection platforms. These platforms include luminescent enzyme-linked immunosorbent assays (ELISAs), bioluminescence resonance energy transfer (BRET)–based sensors, and genetically encoded luminescent biosensors. Increased signal-to-noise ratios, rapid response times, and the ability to monitor dynamic biological processes in live cells are advantages inherent to the approaches mentioned above. Furthermore, novel fusion proteins and optimized expression systems to improve their stability, brightness, and spectral properties have enhanced the performance and pertinence of luminescent biosensors in diverse fields. This review highlights recent progress in RLP-based biosensing, showcasing their implementation for monitoring different contaminants commonly found in food and environmental samples. Future perspectives and potential challenges in these two areas of interest are also addressed, providing a comprehensive overview of the current state and a forecast of the biosensing strategies using recombinant luminescent proteins to come.

 

AnalBioChem_sept24_FrontespizioNews

by ECLectic Project

Graphical Abstract - Electrocatalytic amplification of coreactant electrochemiluminescence using redox mediators

New paper in Electrochimica Acta

Electrocatalytic amplification of coreactant electrochemiluminescence using redox mediators

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

Published in Electrochimica Acta

Abstract

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.

Graphical abstract

Graphical Abstract - Electrocatalytic amplification of coreactant electrochemiluminescence using redox mediators

by ECLectic Project

ECLectic project has received funding from the European Union’s MSCA Doctoral network Horizon Europe programme Grant Agreement Number 101119951.

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