High-resolution imaging of catalytic activity of a single graphene sheet using electrochemiluminescence microscopy

Breathing Laser-Spectral Mapping of Cavity-Enhanced Redox Reactions with Subcellular Resolution

Precise and dynamic observation of redox reactions in living organisms holds significant importance for the study of physiological processes and pathological mechanisms. However, the current technologies still make it challenging to monitor this process in a nondestructive and highly sensitive manner. Herein, we introduced a bioactive laser approach for ultrasensitive and real-time monitoring of intracellular redox reactions. Resazurin, as a popular cell viability assay reagent, has lasing behaviors and photostability, which makes it suitable for the development of bioactive lasers. Due to the strong interactions of light and matter within the laser cavity, subtle changes in resazurin concentration during the redox reaction can be translated into detectable wavelength shifts in the lasing spectrum. With narrow laser peaks, the sensing resolution can reach down to 30 pM per 10 pm wavelength shift. Combined with a scanning platform, we mapped the intracellular and intercellular heterogeneities in metabolism. Further applications in cell identification, oxidative stress assessment, and drug evaluation revealed the universal applicability of this method in cell assays and biomedical analysis, providing insights into disease diagnosis and drug screening.

Photo-crosslinking of doped magic-sized nanoclusters for the construction of enhanced electrochemiluminescence biosensors

Semiconductor magic-sized nanoclusters (MSCs) possess atomic-level compositional precision and ultrasmall dimensions, allowing accurate modulation of electrochemiluminescence (ECL) properties, essential for advanced bioanalytical applications. However, low intrinsic ECL intensity and poor stability in bipolar electrode (BPE)-ECL systems hinder their broader use. In this work, we addressed these limitations through doping and direct optical crosslinking strategies, achieving a 24-fold boost in the ECL signal and a fivefold stability increase for doped (CdS)34:Ag MSCs compared with original (CdS)34 MSCs. The resulting BPE-ECL biosensing platform was used for the sensitive detection of glucose with a linear detection range of 10 μM to 1 mM and a detection limit of 3.64 μM. This approach provides a robust strategy to enhance MSC-based ECL biosensing, paving the way for ultrasensitive, stable biosensors for clinical diagnostics and bioanalysis.

Electrochemiluminescence microscopy for the investigation of peptide interactions within planar lipid membranes

Understanding the interactions between lipid membranes and peptides is crucial for controlling bacterial and viral infections, and developing effective drugs. In this study, we proposed the use of electrochemiluminescence (ECL) microscopy in a solution of [Ru(bpy)3]2+ and tri-n-propylamine to monitor alterations in the lipid membranes due to peptide action. A planar artificial lipid membrane served as a model platform, and its surface was observed using ECL microscopy during exposure to melittin, a representative membrane lytic peptide. Upon exposure to melittin, the light-emitting process of the [Ru(bpy)3]2+/tri-n-propylamine system through the lipid membrane exhibited complex changes, suggesting that stepwise peptide actions can be monitored through the system. Furthermore, wide-field imaging with ECL microscopy provided an effective means of elucidating the membrane surface at the submicron level and revealing heterogeneous changes upon exposure to melittin. This complemented the spatiotemporal information that could not be obtained using conventional electrochemical measurements.

A mini-review on the research progress and application of nanomaterials in electrochemiluminescent sensors in the detection of water environmental pollutants

With the increasingly serious problem of environmental pollution, the development of new and efficient detection technology has become an urgent need. Electrochemiluminescence (ECL) sensors have attracted wide attention in environmental pollution detection due to their advantages of low cost, fast analysis speed, high sensitivity, and good selectivity. At the same time, with the rapid development of nanotechnology, nanomaterials are widely used to construct ECL sensors. Based on the different roles of nanomaterials in the construction of ECL sensors, they can be summarized as (1) nanomaterials for signal amplification; (2) ECL nanoemitters; (3) Nanomaterials as receptors for ECL resonance energy transfer. In this paper, the construction and luminescence mechanism of ECL sensors are discussed from the above three aspects. Finally, the challenges and prospects of nanomaterials ECL sensors in the field of environmental pollution detection in the future are discussed.

Recent Advances in Electrochemiluminescence Visual Biosensing and Bioimaging

Electrochemiluminescence (ECL) is one of the most powerful techniques that meet the needs of analysis and detection in a variety of scenarios, because of its highly analytical sensitivity and excellent spatiotemporal controllability. ECL combined with microscopy (ECLM) offers a promising approach for quantifying and mapping a wide range of analytes. To date, ECLM has been widely used to image biological entities and processes, such as cells, subcellular structures, proteins and membrane transport properties. In this review, we first introduced the mechanisms of several classic ECL systems, then highlighted the progress of visual biosensing and bioimaging by ECLM in the last decade. Finally, the characteristics of ECLM were summarized, as well as some of the current challenges. The future research interests and potential directions for the application of ECLM were also outlooked.

Enhanced Electrochemiluminescence at the Gas/Liquid Interface of Bubbles Propelled into Solution

Electrochemiluminescence (ECL) is typically confined to a micrometric region from the electrode surface. This study demonstrates that ECL emission can extend up to several millimeters away from the electrode employing electrogenerated chlorine bubbles. The mechanism behind this bubble-enhanced ECL was investigated using an Au microelectrode in chloride-containing and chloride-free electrolyte solutions. We discovered that ECL emission at the gas/solution interface is driven by two parallel effects. First, the bubble corona effect facilitates the generation of hydroxyl radicals capable of oxidizing luminol while the bubble is attached to the surface. Second, hypochlorite generated from chlorine sustains luminol emission for over 200 s and extends the emission range up to 5 mm into the solution, following bubble detachment. The new approach can increase the emission intensity of luminol-based assays 5-fold compared to the conventional method. This is demonstrated through a glucose bioassay, using a midrange mobile phone camera for detection. These findings significantly expand the potential applications of ECL by extending its effective range in time and space.

Electrochemiluminescence Microscopy

Electrochemiluminescence (ECL) is rapidly evolving from an analytical method into an optical microscopy. The orthogonality of the electrochemical trigger and the optical readout distinguishes it from classic microscopy and electrochemical techniques, owing to its near-zero background, remarkable sensitivity, and absence of photobleaching and phototoxicity. In this minireview, we summarize the recent advances in ECL imaging technology, emphasizing original configurations which enable the imaging of biological entities and the improvement of the analytical properties by increasing the complexity and multiplexing of bioassays. Additionally, mapping the (electro)chemical reactivity in space provides valuable information on nanomaterials and facilitates deciphering ECL mechanisms for improving their performances in diagnostics and (electro)catalysis. Finally, we highlight the recent achievements in imaging at the ultimate limits of single molecules, single photons or single chemical reactions, and the current challenges to translate the ECL imaging advances to other fields such as material science, catalysis and biology.

Synthesis of Fe-N doped porous carbon/silicate composites regulated by minerals in coal gasification fine slag for synergistic electrocatalytic treatment of phenolic wastewater

Coal gasification fine slag (CGFS), as a difficult-to-dispose solid waste in the coal chemical industry, consists of minerals and residual carbon. Due to the aggregate structure of minerals blocking pores and encapsulating active substances, the high-value utilization of CGFS still remains a challenge. Based on the intrinsic characteristics of CGFS, this study synthesized Fe-N doped porous carbon/silicate composites (Fe-NC) by alkali activation and pyrolysis for electrocatalytic degradation of phenolic wastewater. Meanwhile, minerals were utilized to regulate the surface chemical and pore structure, turning their disadvantages into advantages, which caused a sharp increase in m-cresol mineralization. The positive effect of minerals on composite properties was investigated by characterization techniques, electrochemical analyses and density functional theory (DFT) calculations. It was found that the mesoporous structure of the mineral-regulated composites was further developed, with more carbon defects and reactive substances on its surface. Most importantly, silicate mediated iron conversion through strong interaction with H2O2, high work function gradient with electroactive iron, and excellent superoxide radical (•O2-) production capacity. It effectively improved the reversibility and kinetics of the entire electrocatalytic reaction. Within the Fe-NC311 electrocatalytic system, the m-cresol removal rate reached 99.55 ± 1.24%, surpassing most reported Fe-N-doped electrocatalysts. In addition, the adsorption and electrooxidation experiment confirmed that the synergistic effect of Fe-N doped porous carbon and silicate simultaneously promoted the capture of pollutants and the transformation of electroactive molecules, and hence effectively shortened the diffusion path of short-lived radicals, which was further supported by molecular dynamics simulation. Therefore, this research provides new insights into the problem of mineral limitations and opens an innovative approach for CGFS recycling and environmental remediation.

Shadow electrochemiluminescence imaging of giant liposomes opening at polarized electrodes

In this work, the release of giant liposome (∼100 μm in diameter) content was imaged by shadow electrochemiluminescence (ECL) microscopy. Giant unilamellar liposomes were pre-loaded with a sucrose solution and allowed to sediment at an ITO electrode surface immersed in a solution containing a luminophore ([Ru(bpy)3]2+) and a sacrificial co-reactant (tri-n-propylamine). Upon polarization, the electrode exhibited illumination over its entire surface thanks to the oxidation of ECL reagents. However, as soon as liposomes reached the electrode surface, dark spots appeared and then spread over time on the surface. This observation reflected a blockage of the electrode surface at the contact point between the liposome and the electrode surface, followed by the dilution of ECL reagents after the rupture of the liposome membrane and release of its internal ECL-inactive solution. Interestingly, ECL reappeared in areas where it initially faded, indicating back-diffusion of ECL reagents towards the previously diluted area and thus confirming liposome permeabilization. The whole process was analyzed qualitatively and quantitatively within the defined region of interest. Two mass transport regimes were identified: a gravity-driven spreading process when the liposome releases its content leading to ECL vanishing and a diffusive regime when ECL recovers. The reported shadow ECL microscopy should find promising applications for the imaging of transient events such as molecular species released by artificial or biological vesicles.

Nanoscale Luminescence Imaging/Detection of Single Particles: State-of-the-Art and Future Prospects

Single-particle-level measurements, during the reaction, avoid averaging effects that are inherent limitations of conventional ensemble strategies. It allows revealing structure-activity relationships beyond averaged properties by considering crucial particle-selective descriptors including structure/morphology dynamics, intrinsic heterogeneity, and dynamic fluctuations in reactivity (kinetics, mechanisms). In recent years, numerous luminescence (optical) techniques such as chemiluminescence (CL), electrochemiluminescence (ECL), and fluorescence (FL) microscopies have been emerging as dominant tools to achieve such measurements, owing to their diversified spectroscopy principles, noninvasive nature, higher sensitivity, and sufficient spatiotemporal resolution. Correspondingly, state-of-the-art methodologies and tools are being used for probing (real-time, operando, in situ) diverse applications of single particles in sensing, medicine, and catalysis. Herein, we provide a concise and comprehensive perspective on luminescence-based detection and imaging of single particles by putting special emphasis on their basic principles, mechanistic pathways, advances, challenges, and key applications. This Perspective focuses on the development of emission intensities and imaging based individual particle detection. Moreover, several key examples in the areas of sensing, motion, catalysis, energy, materials, and emerging trends in related areas are documented. We finally conclude with the opportunities and remaining challenges to stimulate further developments in this field.

Optics Determines the Electrochemiluminescence Signal of Bead-Based Immunoassays

Electrochemiluminescence (ECL) is an optical readout technique that is successfully applied for the detection of biomarkers in body fluids using microbead-based immunoassays. This technology is of utmost importance for in vitro diagnostics and thus a very active research area but is mainly focused on the quest for new dyes and coreactants, whereas the investigation of the ECL optics is extremely scarce. Herein, we report the 3D imaging of the ECL signals recorded at single microbeads decorated with the ECL labels in the sandwich immunoassay format. We show that the optical effects due to the light propagation through the bead determine mainly the spatial distribution of the recorded ECL signals. Indeed, the optical simulations based on the discrete dipole approximation compute rigorously the electromagnetic scattering of the ECL emission by the microbead and allow for reconstructing the spatial map of ECL emission. Thus, it provides a global description of the ECL chemical reactivity and the associated optics. The outcomes of this 3D imaging approach complemented by the optical modeling provide insight into the ECL optics and the unique ECL chemical mechanism operating on bead-based immunoassays. Therefore, it opens new directions for mechanistic investigations, ultrasensitive ECL bioassays, and imaging.

Dynamic Mapping of Electrochemiluminescence Reactivity in Space: Application to Bead-Based Assays

As an electrochemical technique offering an optical readout, electrochemiluminescence (ECL) evolved recently into a powerful microscopy technique with the visualization of a wide range of microscopic entities. However, the dynamic imaging of transient ECL events did not receive intensive attention due to the limited number of electrogenerated photons. Here, the reaction kinetics of the model ECL bioassay system was revealed by dynamic imaging of single [Ru(bpy)3]2+-functionalized beads in the presence of the efficient tripropylamine coreactant. The time profile behavior of ECL emission, the variations of the ECL layer thickness, and the position of maximum ECL intensity over time were investigated, which were not achieved by static imaging in previous studies. Moreover, the dynamics of the ECL emission were confronted with the simulation. The reported dynamic ECL imaging allows the investigation of the ECL kinetics and mechanisms operating in bioassays and cell microscopy.

Site-selective heat boosting electrochemiluminescence for single cell imaging

In operando visualization of local electrochemical reactions provides mechanical insights into the dynamic transport of interfacial charge and reactant/product. Electrochemiluminescence is a crossover technique that quantitatively determines Faraday current and mass transport in a straightforward manner. However, the sensitivity is hindered by the low collision efficiency of radicals and side reactions at high voltage. Here, we report a site-selective heat boosting electrochemiluminescence microscopy. By generating a micron-scale heat point in situ at the electrode-solution interface, we achieved an enhancement of luminescence intensity up to 63 times, along with an advance of 0.2 V in applied voltage. Experimental results and finite element simulation demonstrate that the fundamental reasons are accelerated reaction rate and thermal convection via a photothermal effect. The concentrated electrochemiluminescence not only boosts the contrast of single cells by 20.54 times but also enables the site-selective cell-by-cell analysis of the heterogeneous membrane protein abundance. This electrochemical visualization method has great potential in the highly sensitive and selective analysis of local electron transfer events.

Screening for electrically conductive defects in thin functional films using electrochemiluminescence

Multifunctional thin films in energy-related devices often must be electrically insulating where a single nanoscale defect can result in complete device-scale failure. Locating and characterizing such defects presents a fundamental problem where high-resolution imaging methods are needed to find defects, but imaging with high spatial resolution limits the field of view and thus the measurement throughput. Here, we present a novel high-throughput method for detecting sub-micron defects in insulating thin films by leveraging the electrochemiluminescence (ECL) of luminol. Through a systematic study of reagent concentrations, buffers, voltage, and excitation time, we identify optimized conditions under which it is possible to detect sub-micron defects at high-throughput. Extrapolating from the signal to background observed for detecting 440 nm wide lines and 620 nm diameter circles, we estimate the minimum detectable features to be lines as narrow as 2.5 nm in width and pinholes as small as 70 nm in radius. We further explore this method by using it to characterize a nominally insulating poly(phenylene oxide) film and find conductive defects that are cross-correlated with high-resolution atomic force microscopy to provide feedback to synthesis. Given this assay's inherent parallelizability and scalability, it is expected to have a major impact on the automated discovery of multifunctional films.

Self-Enhanced Electrochemiluminescence Imaging System Based on the Accelerated Generation of ROS under Ultrasound

Electrochemiluminescence (ECL) imaging, as an optical technology, has been developed at full tilt in the field of life science and nanomaterials. However, the relatively low ECL intensity or the high co-reactant concentration needed in the electrochemical reaction blocks its practical application. Here, we developed an ECL imaging system based on the rGO-TiO_2-x composite material, where the co-reactant, reactive oxygen species (ROS), is generated in situ under the synergetic effect of of ultrasound (US) and electric irradiation. The rGO-TiO_2-x composites facilitate the separation of electron (e^-) and hole (h⁺) pairs and inhibit recombination triggered by external US irradiation due to the high electroconductivity of rGO and oxygen-deficient structures of TiO₂, thus significantly boosting ROS generation. Furthermore, the increased defects on rGO accelerate the electron transfer rate, improving the electrocatalytic performance of the composite and forming more ROS. This high ultrasonic-electric synergistic efficacy is demonstrated through the enhancement of photon emission. Compared with the luminescence intensity triggered by US irradiation and electric field, an enhancement of ∼20-fold and 10-fold of the US combined with electric field-triggered emission is observed from this composite. Under the optimized conditions, using dopamine (DA) as a model target, the sensitivity of the US combined ECL strategy for detection of DA is two orders of magnitude higher than that of the ECL method. The successful detection of DA at low concentrations makes us believe that this strategy provides the possibility of applying ECL imaging for cellular single-molecule analysis and cancer therapy.

Newly Developed Electrochemiluminescence Based on Bipolar Electrochemistry for Multiplex Biosensing Applications: A Consolidated Review

Recently, there has been an upsurge in the extent to which electrochemiluminescence (ECL) working in synergy with bipolar electrochemistry (BPE) is being applied in simple biosensing devices, especially in a clinical setup. The key objective of this particular write-up is to present a consolidated review of ECL-BPE, providing a three-dimensional perspective incorporating its strengths, weaknesses, limitations, and potential applications as a biosensing technique. The review encapsulates critical insights into the latest and novel developments in the field of ECL-BPE, including innovative electrode designs and newly developed, novel luminophores and co-reactants employed in ECL-BPE systems, along with challenges, such as optimization of the interelectrode distance, electrode miniaturization and electrode surface modification for enhancing sensitivity and selectivity. Moreover, this consolidated review will provide an overview of the latest, novel applications and advances made in this field with a bias toward multiplex biosensing based on the past five years of research. The studies reviewed herein, indicate that the technology is rapidly advancing at an outstanding purse and has an immense potential to revolutionize the general field of biosensing. This perspective aims to stimulate innovative ideas and inspire researchers alike to incorporate some elements of ECL-BPE into their studies, thereby steering this field into previously unexplored domains that may lead to unexpected, interesting discoveries. For instance, the application of ECL-BPE in other challenging and complex sample matrices such as hair for bioanalytical purposes is currently an unexplored area. Of great significance, a substantial fraction of the content in this review article is based on content from research articles published between the years 2018 and 2023.

Bimodal Electrochemiluminescence Microscopy of Single Cells

Electrochemiluminescence (ECL) microscopy is an emerging technique with new applications such as imaging of single entities and cells. Herein, we have developed a bimodal and bicolor approach to record both positive ECL (PECL: light-emitting object on dark background) and shadow label-free ECL (SECL: nonemissive object shadowing the background luminescence) images of single cells. This bimodal approach is the result of the simultaneous emissions of [Ru(bpy)₃]²⁺ used to label the cellular membrane (PECL) and [Ir(sppy)₃]^3- dissolved in solution (SECL). By spectrally resolving the ECL emission wavelengths, we recorded the images of the same cells in both PECL and SECL modes using the [Ru(bpy)₃]²⁺ (λ_max = 620 nm) and [Ir(sppy)₃]^3- (λ_max = 515 nm) luminescence, respectively. PECL shows the distribution of the [Ru(bpy)₃]²⁺ labels attached to the cellular membrane, whereas SECL reflects the local diffusional hindrance of the ECL reagents by each cell. The high sensitivity and surface-confined features of the reported approach are demonstrated by imaging cell-cell contacts during the mitosis process. Furthermore, the comparison of PECL and SECL images demonstrates the differential diffusion of tri-n-propylamine and [Ir(sppy)₃]^3- through the permeabilized cell membranes. Consequently, this dual approach enables the imaging of the morphology of the cell adhering on the surface and can significantly contribute to multimodal ECL imaging and bioassays with different luminescent systems.

Direct Visualization of Nanoconfinement Effect on Nanoreactor via Electrochemiluminescence Microscopy

Nanoconfinement in mesoporous nanoarchitectures could dramatically change molecular transport and reaction kinetics during electrochemical process. A molecular-level understanding of nanoconfinement and mass transport is critical for the applications, but a proper route to study it is lacking. Herein, we develop a single nanoreactor electrochemiluminescence (SNECL) microscopy based on Ru(bpy)₃ ²⁺ -loaded mesoporous silica nanoparticle to directly visualize in situ nanoconfinement-enhanced electrochemical reactions at the single molecule level. Meanwhile, mass transport capability of single nanoreactor, reflected as long decay time and recovery ability, is monitored and simulated with a high spatial resolution. The nanoconfinement effects in our system also enable imaging single proteins on cellular membrane. Our SNECL approach may pave the way to decipher the nanoconfinement effects during electrochemical process, and build bridges between mesoporous nanoarchitectures and potential electrochemical applications.

In Situ Confocal Fluorescence Lifetime Imaging of Nanopore Electrode Arrays with Redox Active Fluorogenic Amplex Red

Direct imaging of electrochemical processes on electrode surfaces is a central part of understanding spatially heterogeneous electrochemical processes on the surfaces. Herein, we report a strategy for the spatially resolved imaging of local faradaic processes on nanoscale electrochemical interfaces. This strategy is based on fluorescence lifetime imaging microscopy (FLIM) with the use of Amplex Red as a fluorogenic redox probe. After verifying the capability of Amplex Red for fluorescence lifetime imaging, we demonstrated the turn-on FLIM-based imaging of faradaic processes on the electrochemical interfaces of different dimensions. In particular, we achieved spatially resolved visualization of the local electrochemical processes occurring on even nanopore electrode arrays as well as conventional microelectrodes, including disk-shaped ultramicroelectrodes and interdigitated array microelectrodes.

Advances in electrochemiluminescence for single-cell analysis

Recent years have witnessed the emergence of innovative analytical methods with high sensitivity and spatiotemporal resolution that allowed qualitative and quantitative analysis to be carried out at single-cell and subcellular levels. Electrochemiluminescence (ECL) is a unique chemiluminescence of high-energy electron transfer triggered by electrical excitation. The ingenious combination of electrochemistry and chemiluminescence results in the distinct advantages of high sensitivity, a wide dynamic range and good reproducibility. Specifically, single-cell ECL (SCECL) analysis with excellent spatiotemporal resolution has emerged as a promising toolbox in bioanalysis for revealing individual cells' heterogeneity and stochastic processes. This review focuses on advances in SCECL analysis and bioimaging. The history and recent advances in ECL probes and strategies for system design are briefly reviewed. Subsequently, the latest advances in representative SCECL analysis techniques for bioassays, bioimaging and therapeutics are also highlighted. Then, the current challenges and future perspectives are discussed.

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.

MXene-Derived Quantum Dot@Gold Nanobones Heterostructure-Based Electrochemiluminescence Sensor for Triple-Negative Breast Cancer Diagnosis

MXene material has been gradually studied in recent years due to its fascinating characteristics. This work developed a novel MXene-derived quantum dots (MQDs) @gold nanobones (Au NBs) heterostructure as the electrochemiluminescence (ECL) sensor. First, MXene and MQDs were synthesized via the green preparation process, which avoided the harm of hydrofluoric acid to humans and the environment. There was a strong ECL signal enhancement in the MQD@Au NBs heterostructure. On the one hand, Au NBs with surface plasmon resonance (SPR) effect acted as an "electronic regulator" that can transfer electrons to itself to control over-injection of electrons into the conduction band of MQDs. The luminous signal of MQDs can be efficiently generated and significantly amplified in the ECL sensing process. On the other hand, the work function of MQDs with excellent conductivity was relatively close to that of Au NBs in the heterostructure. So, ECL quenching caused by short-distance electron transfer between luminophore and Au nanomaterial has been effectively suppressed. The MQD@Au NBs heterostructure-based ECL sensing system was applied to determine miRNA-26a in the serum of patients with triple-negative breast cancer. It not only provides ideas for the green synthesis of MXene but also provides a guide for the application of MQD@Au NBs heterostructure in the field of ECL sensing.

Understanding the Synergistic Oxidation in Dichalcogenides through Electrochemiluminescence Blinking at Millisecond Resolution

The oxidation of transition metal dichalcogenides (TMDCs) has been extensively studied and applied in electronics, optics, and energy sources because of its tunable structure and performance. However, due to the lack of appropriate technology, dynamically observe the oxidation process remains an arduous task. Herein, the synergistic oxidation between edge and basal plane in molybdenum disulfide (MoS₂ ) is observed through electrogenerated chemiluminescence (ECL) blinking with a millisecond resolution. In addition, the ECL method provides a simple, convenient, and quick way to judge structural changes. The transient elevation of the ECL intensity proved the intermittent doping of oxygen at MoS₂ , which generates O-atom active sites. High ECL intensity enhanced from the produced hydroperoxide intermediates eases the monitoring of MoS₂ particles. Further study shows that the formation of sulfur vacancies at MoS₂ , by the edge activation of hydrogen peroxide and the migration of oxygen to the basal plane, is more conducive to oxygen doping that favors the formation of MoOMo as new active sites to induce bursts. The revealing of sulfur vacancy-governed blinking from MoS₂ indicates a complex interaction between oxygen and MoS₂ . The same phenomenon is observed on tungsten disulfide (WS₂ ), which provides new information about the oxidation feature of 2D dichalcogenides.

Single-nanoparticle spectroelectrochemistry studies enabled by localized surface plasmon resonance

This review describes recent progress of spectroelectrochemistry (SEC) analysis of single metallic nanoparticles (NPs) which have strong surface plasmon resonance properties. Dark-field scattering (DFS), photoluminescence (PL), and electrogenerated chemiluminescence (ECL) are three commonly used optical methods to detect individual NPs and investigate their local redox activities in an electrochemical cell. These SEC methods are highly dependent on a strong light-scattering cross-section of plasmonic metals and their electrocatalytic characteristics. The surface chemistry and the catalyzed reaction mechanism of single NPs and their chemical transformations can be studied using these SEC methods. Recent progress in the experimental design and fundamental understanding of single-NP electrochemistry and catalyzed reactions using DFS, PL, and ECL is described along with selected examples from recent publications in this field. Perspectives on the challenges and possible solutions for these SEC methods and potential new directions are discussed.

Analyzing Near-Infrared Electrochemiluminescence of Graphene Quantum Dots in Aqueous Media

Mechanisms of emissions, especially electrochemiluminescence (ECL), for graphene quantum dots (GQDs) are poorly understood, which makes near-infrared (NIR)-emitting GQDs difficult to create. To explore this poorly understood NIR ECL, two GQDs, nitrogen-doped GQDs (GQD-1) and nitrogen- and sulfur-doped ones (GQD-2), were prepared by a simple one-step solvothermal reaction with similar core structures but different surface states. The GQDs were analyzed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. Photoluminescence results, with a comparable quantum efficiency of 13% to strong luminophores in aqueous media, suggested a mechanism that the emission mainly depends on the core structure while slightly adjusted by the heteroatom doping. ECL of GQD-2 dispersed in aqueous media with K₂S₂O₈ as the coreactant was measured by means of ECL-voltage curves and ECL spectroscopy, demonstrating strong NIR emissions between 680 and 870 nm, with a high ECL efficiency of 13% relative to that of the Ru(bpy)₃²⁺/K₂S₂O₈ system. Interestingly, ECL is generated by surface excited states emitting light at a much longer wavelength in the NIR region. The easily prepared GQD-2 has several advantages such as low cost and quite strong NIR-ECL in aqueous media, with which wide applications in biodetection are anticipated.