Bipolar electrochemical sensor with perylene diimide-based cathodic luminophore for dopamine detection and imaging

Bipolar electrochemical microscopy (BEM), which visualizes the concentration distribution of molecular species in biological systems by electrochemiluminescence (ECL), is expected to be applied to the high-spatiotemporal-resolution imaging of biomolecules, enabling the analysis of cellular functions. In the past, the molecular species that could be imaged by BEM were generally restricted to oxidized molecules due to the limitation derived from the ECL mechanism of the luminophore. Recently, the imaging of dopamine (DA), a reduced molecule, was achieved using Ru (bpy)32+/glutathione disulfide (GSSG) as a cathodic luminophore. However, a large driving voltage was required for ECL generation, resulting in a low S/N ratio. In this study, we employed N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (PDI-CH3)/potassium peroxodisulfate (K2S2O8), which is a cathodic luminophore that can be reduced at a nobler potential to produce ECL than [Ru(bpy)3]2+/GSSG. First, the ECL mechanism of PDI-CH3/K2S2O8 was elucidated by using a PDI-CH3 drop-cast glassy carbon electrode (GCE) immersed in K2S2O8 solution as the working electrode in a 3-electrode system. The PDI-CH3 drop-casted GCE, a single closed bipolar electrode (c-BPE), was used as the cathode in the successful quantification of 50-500 μmol L-1 DA in a sample chamber in which a c-BPE anode was immersed, resulting in a high S/N. The selective detection of DA in the presence of ascorbic acid was achieved by modifying the anode with Nafion. Finally, DA imaging was demonstrated using a commercially available anisotropic conducting film with PDI-CH3 coating on the cathode surface as a c-BPE array. The change in the concentration distribution in the inflow of DA was successfully imaged based on the change in the ECL intensity at the c-BPE cathode. This BEM system is expected to be useful for DA imaging of the brain.

Promoting effect of TiVC MXene on cathodic electrogenerated chemiluminescence of Ru(bpy)32+ and its application in the sensitive detection of sulfite

The enhanced cathodic ECL of Ru(bpy)32+ at a bimetallic element MXenes (TiVC MXene) modified electrode in neutral aqueous condition is reported. TiVC MXene significantly catalyzed the oxygen reduction reaction (ORR) as well as the electrochemical reduction of Ru(bpy)32+ to produce reactive oxygen species and Ru(bpy)3+. The obtained hydroxyl radical (OH∙) not only oxidized Ru(bpy)3+ to generate Ru(bpy)32+* and emit light through coreactant pathway, but also oxidized Ru(bpy)32+ to Ru(bpy)33+, which caused an annihilation ECL reaction. As a result, two pathways occurred simultaneously to generate strong cathodic ECL signal. Sulfite removes the dissolved oxygen in water and reduces the occurrence of ORR, which prohibits the generation of OH∙ to decrease the ECL signal. The decrement of ECL intensity varied linearly with the concentration of sulfite in the range 2 nM to 50 μM with a detection limit of 0.14 nM (3σ). The proposed sensor exhibited good analytical performance, and could be used in the detection of sulfite in real samples. The results revealed that the electrocatalytic behavior of TiVC MXene is the key factor for strong cathodic Ru(bpy)32+ ECL, which provides new application in ECL sensing field.

Highly Sensitive Detection of the Insecticide Azamethiphos by Tris(2,2'-bipyridine)ruthenium(II) Electrogenerated Chemiluminescence

Azamethiphos (AZA) is an insecticide and neurotoxic agent that causes the inhibition of acetylcholinesterase (AChE). AChE is a vital enzyme for neurotransmission because it metabolizes acetylcholine neurotransmitter at the synaptic cleft and terminates synaptic transmission. It is worth mentioning that organophosphates and carbamates inhibit AChE. These AChE inhibitors bind to the active site of the enzyme and inactivate it, leading to paralysis and death. Herein, for the first time, we develop a sensitive, low-cost, and rapid electrogenerated chemiluminescence (ECL) system for the detection of AZA. The designed ECL sensor was applied for the highly sensitive detection of AZA with a wide dynamic range (from 0.1 μM to 1000 μM) and low detection limit of 0.07 μM (S/N = 3). The practical utility of the sensor demonstrates high recoveries (96-102%) in real samples of lake water and wastewater.

Recent advances in electrochemiluminescence luminophores

Electrochemiluminescence (ECL) has continued to receive considerable attention in various applications, owing to its intrinsic advantages such as near-zero background response, wide dynamic range, high sensitivity, simple instrumentation, and low cost. The ECL luminophore is one of the most significant components during the light generation processes. Despite significant progress that has been made in the synthesis of new luminophores and their roles in resolving various challenges, there are few comprehensive summaries on ECL luminophores. In this review, we discuss some of the recent advances in organic, metal complexes, nanomaterials, metal oxides, and near-infrared ECL luminophores. We also emphasize their roles in tackling various challenges with illustrative examples that have been reported in the last few years. Finally, perspective and some unresolved challenges in ECL that can potentially be addressed by introducing new luminophores have also been discussed. Graphical abstract.

Bimodal Electrogenerated Chemiluminescence of the Luminol/Dicyclohexylamine (DCHA) System: A Novel and Highly Sensitive Detection of DCHA via ECL-Flow Injection Analysis

Though luminol is one of the most prominent and extensively studied luminophores in ECL studies, only H₂O₂ has been widely used as a co-reactant. This limits the variety of applications because of the short-time radical stability and low quantum efficiency. In the present work, we identified dicyclohexylamine (DCHA) as a new and highly efficient anodic co-reactant in ECL for the luminol molecule. The electrochemical and ECL behavior of the luminol/DCHA system was studied on a simple bare GCE surface, which results in two anodic ECL peaks at the potential region of +0.38 and +0.94 V vs Ag/AgCl. The evidence of (DCHA^•+) and O₂^•- generated in the system was detected via flat-cell electron spin resonance (ESR) spectroscopy experiments at ∼20 °C. Using the bimodal ECL system, the highly sensitive detection of luminol was achieved with the detection limit down to 1.5 pM. Further, a homebuilt electrochemiluminescent detector coupled with a flow injection analysis (ECL-FIA) system was adopted to detect the DCHA contaminant in harvested honey, which achieved higher detection and sensitivity under the optimized experimental conditions. DCHA was detected in the range of 10 nM to 100 μM with the detection limit of 2 nM (S/N = 3). The present findings of new luminol/DCHA ECL signals produced a strong ECL emission, which leads to a greater potential to meet the fast-developing analytical application of a luminol-based ECL system.

Co-reactant-free self-enhanced solid-state electrochemiluminescence platform based on polyluminol-gold nanocomposite for signal-on detection of mercury ion

Development of a self-enhanced solid-state ECL platform creates a straightforward experimental design for the fabrication of point-of-care applications. Herein, we develop a promising method for self-enhanced solid-state ECL platform of polyluminol gold nanocomposite on glassy carbon electrode [(PL-Au)_nano/GCE] via simple one-step electrochemical deposition process without involving any additional co-reactants. The presence of gold nanoparticles (AuNPs) augments the electron transfer kinetics of PL (polyluminol) and enhances the solid-state ECL intensity and promotes label-free, excellent sensitivity, and selectivity to detect Hg²⁺ in physiological pH through signal-on mode. Unlike pristine PL/GCE, electrochemically co-deposited AuNPs in the (PL-Au)_nano/GCE composite, enable the co-reactant accelerator by improving the catalytic activity of PL towards oxygen reduction reaction (ORR) yielding in-situ ROS (co-reactant) generation. Further, the ECL intensity of (PL-Au)_nano/GCE composite, gradually increases with each addition of Hg²⁺ ion. This is because of the formation of an amalgamation of Au-Hg on (PL-Au)_nano/GCE composite surface which further accelerates the yield of in-situ ROS and enhances the intensity of ECL. Whereas no ECL signals changes were observed for PL/GCE composite. The proposed self-enhanced solid-state ECL platform is selectively sensing the Hg²⁺ ion in the linear range of 0.3–200 nM with a detection limit of 0.1 nM. The demonstrated (PL-Au)_nano/GCE platform might pave new avenues for further studies in the solid-state ECL platform which could be more useful in on-site monitoring of clinical bioassay and immunosensors.

Mechanistic Insight into a Novel Ultrasensitive Nicotine Assay Base on High-Efficiency Quenching of Gold Nanocluster Cathodic Electrochemiluminescence

Monitoring nicotine concentrations in human fluids is extremely crucial owing to the harmful effect of nicotine on human health. Herein, it is shown that nicotine could quench the cathodic electrochemiluminescence (ECL) of gold nanoclusters (AuNCs) with high efficiency. The ECL quenching mechanism of nicotine was studied in detail using various experimental tools and theoretical calculations. It was concluded that the strongly oxidizing intermediate SO₄^•-, produced from K₂S₂O₈, could oxidized nicotine, resulting in ECL emission quenching. On the basis of this high-efficiency ECL quenching of the AuNCs/K₂S₂O₈ system, a recyclable, ultrasensitive, and selective ECL sensing platform for nicotine detection was proposed. Even in the absence of any complex signal amplification techniques, the ECL sensor for nicotine detection showed an unprecedentedly low detection limit of 7.0 × 10^-13 M (S/N = 3) and a wide linear range over 8 orders of magnitude. Most remarkably, it could be successfully used for nicotine detection in human urine samples. This is expected to promote the investigations and applications on nicotine-related diseases. We believe that the proposed ECL platform can hold great prospects for commercialization in biomedical fields and tobacco industries.

Gold nanoparticles decorated carbon nitride nanosheets as a coreactant regulate the conversion of the dual-potential electrochemiluminescence of Ru(bpy)32+ for Hg2+ detection

Dual-potential electrochemiluminescence of Ru(bpy)₃²⁺ for Hg²⁺ assay using Au–g-C₃N₄ NSs as on-electrode coreactant.