Electrochemiluminescence Imaging Research Articles

High-Efficient Electrochemiluminescence of BCNO Quantum Dot-Equipped Boron Active Sites with Unexpected Catalysis for Ultrasensitive Detection of MicroRNA.

Herein, the boron radical active sites of boron carbon oxynitride quantum dots (BCNO QDs) are electrically excited to produce boron radicals (B•) for catalyzing peroxydisulfate (S2O82-) as a coreactant to accelerate the generation of abundant sulfate radicals (SO4•-) for significant enhancement in the electrochemiluminescence (ECL) efficiency of BCNO QDs, which overcome the defect of traditional carbon-based QDs with low ECL efficiency. Impressively, under extremely low concentration of S2O82- solution, the BCNO QDs/S2O82- system could exhibit high ECL emission, realizing environmental friendliness and excellent biocompatibility for sensitive bioanalysis. As a proof-of-concept, BCNO QDs, a new generation of ECL emitters with high ECL efficiency, were successfully used in the ultrasensitive determination of microRNA-21, which pushes the exploration of new ECL emitters and broadens the application in the field of clinical diagnosis, ECL imaging, and molecular devices.

Wireless Enhanced Electrochemiluminescence at a Bipolar Microelectrode in a Solid-State Micropore

The combination of bipolar electrochemistry (BE), as a wireless electrochemical approach, and of electrochemiluminescence (ECL) as an imaging readout is a successful strategy with a wide range of analytical applications. However, small conductive entities such as micrometric and nanometric objects are particularly difficult to polarize by BE since they require extremely high electric fields. In order to circumvent this issue due to intrinsic limitations of BE, we elaborated a solid-state micropore, decorated with a rhombus-shaped gold microelectrode. The electric field strength was concentrated inside the solid-state micropore where the conductive gold microelectrode was precisely located and acted as a bipolar light-emitting device. This original configuration allowed achieving adequate polarization of the gold microelectrode in a wireless manner, which led locally to ECL emission. ECL imaging shows that light was generated by the bipolar microelectrode in the center of the micropore. ECL emission could be achieved by imposing a potential value (10 V) to the feeder electrodes that is more than 2 orders of magnitude lower than those required without the micropore. The reported ECL approach opens exciting perspectives for the development of original wireless bioanalytical applications and dynamic bipolar experiments with small objects passing through the pores.

Alternate reporting surfaces in closed bipolar electrode system: A strategy forelectrochemiluminescence sensing of both redox processes

Bipolar electrode (BPE) combining with electrochemiluminescence (ECL) has been a very efficient tool for chemical and biological sensing, catalysts screening, etc. In general, however，These commonly used BPE-ECL sensing strategies could only monitor alternative oxidation or reduction behaviors of targets. To address this issue, a closed BPE system with alternate ECL reporting surfaces between BPE pole and driving electrode was constructed for monitoring both of the redox processes of targets. The feasibility and universality of this strategy were elaborated by studying the electrochemical (EC) and ECL behaviors of this closed BPE system. Then, based on the alternate ECL reporting surfaces, both of the redox processes were successfully detected by this closed BPE-ECL sensor, which had a good linear relationship between the concentrations and the corresponding ECL signals. Furthermore, take advantage of the visual ECL imaging, high-throughput determination of the redox of targets was successfully carried out by an array of the closed BPE system with alternate reporting surfaces.

Fe3O4 NP@ZIF-8/MoS2 QD-based electrochemiluminescence with nanosurface energy transfer strategy for point-of-care determination of ATP

Herein, Fe3O4 NP@ZIF-8/MoS2 QD-based electrochemiluminescence (ECL) biosensor with nanosurface energy transfer strategy was successfully developed for point-of-care determination of ATP. With the porous structure and poor electron transfer ability, Fe3O4 NP@ZIF-8 complex was first used as an excellent catalyst in ECL. The complex catalyzed the coreactant for more free radicals and hindered the quenching effect of Fe3O4 nanoparticles (NPs) on quantum dots (QDs). In ECL-nanosurface energy transfer (NSET) system, through the specific binding of complementary DNA linked to MoS2 QDs (QDs-cDNA) and aptamer linked to Au NPs, interaction between the point dipole of MoS2 QDs and the collective dipoles of Au NPs quenched ECL signal. When ATP was captured by aptamer, the ECL-NSET system was taken apart, which resulted in the recovery of ECL signal. Moreover, changes of the ECL imaging can be captured by a smartphone, which enabled point-of-care determination of ATP from 0.05 nmol L−1 to 200 nmol L−1 with LOD of 0.015 nmol L−1. With superior specificity and stability, the sensing system showed significant potential about the application of catalysts coated with ZIF and NSET in point-of-care ECL determination.

Insights into the mechanism of coreactant electrochemiluminescence facilitating enhanced bioanalytical performance

Electrochemiluminescence (ECL) is a powerful transduction technique with a leading role in the biosensing field due to its high sensitivity and low background signal. Although the intrinsic analytical strength of ECL depends critically on the overall efficiency of the mechanisms of its generation, studies aimed at enhancing the ECL signal have mostly focused on the investigation of materials, either luminophores or coreactants, while fundamental mechanistic studies are relatively scarce. Here, we discover an unexpected but highly efficient mechanistic path for ECL generation close to the electrode surface (signal enhancement, 128%) using an innovative combination of ECL imaging techniques and electrochemical mapping of radical generation. Our findings, which are also supported by quantum chemical calculations and spin trapping methods, led to the identification of a family of alternative branched amine coreactants, which raises the analytical strength of ECL well beyond that of present state-of-the-art immunoassays, thus creating potential ECL applications in ultrasensitive bioanalysis.

Electrochemiluminescence Imaging for the Morphological and Quantitative Analysis of Living Cells under External Stimulation.

In this work, a simple electrochemiluminescence (ECL) imaging method based on the cell shield of the ECL emission was developed for the morphological and quantitative analysis of living cells under external stimulation. ECL images of MCF-7 cells cultured on or captured at the glassy carbon electrode (GCE) surface in a solution of tris(2,2'-bipyridyl)ruthenium(II)-tri-n-propylamine were recorded. Important morphological characteristics of living cells, including cell shape, cell area, average cell boundary, and junction distance between two adjacent cells, were directly obtained using the developed negative ECL imaging method. The ECL images revealed gradual morphological changes in cells on the GCE surface. During the course of H2O2 stimulation of cells on the GCE surface, cells shrunk, rounded up, disengaged from surrounding cells, and finally detached from the electrode surface. During the course of electrical stimulation (0.8 V), the cells on the GCE surface exhibited aggregation as demonstrated by increases in the average cell boundary and decreases in the junction distance between two adjacent cells. Additionally, a quantitative method for the sensitive determination of MCF-7 cells with a limit of detection of 29 cells/mL was developed using the negative ECL imaging strategy. This work demonstrates that the proposed negative ECL imaging strategy is a promising approach to assess important morphological characteristics of living cells during the course of external stimulation and to obtain quantitative information on cell concentrations in solution.

Electrochemiluminescence imaging of latent fingerprints by electropolymerized luminol

An efficient method has been developed for visualizing latent fingerprints by spatially selective electropolymerization of luminol on the ITO electrode. The fingerprint deposited on the electrode surface functions as a mask so that polyluminol is formed on the bare electrode surface. Therefore, electrochemiluminescence is only generated between the ridges of fingerprint, eventually yielding a negative ECL image. This method is easy to operate and safe to examiners. In addition, the second- and third-level details of fingerprints can be well resolved, indicating the potential application for personal identification and forensic investigation.

Recent Advances in Visual Electrochemiluminescence Analysis

Due to the advantages of low background interference and high sensitivity, electrochemiluminescence (ECL)-based sensor has developed rapidly in recent years. The ECL sensors have shown the potential in the ultrasensitive and real-time analysis. Especially, the visual ECL analysis, including visual detection, cell imaging and single particle analysis, has offered many unique sensing platforms for analysis research and point-of-care testing. The high throughput ECL image analysis can not only provide ECL intensity but also reveal more information about the chemical reaction activity of particle and the physiological processes of cell operation. Therefore, we review the novel ECL luminophore, sensing systems, and successful applications in the visual ECL detection and imaging in this paper. First, the different ECL luminophore is summarized. Second, we discuss the ECL sensing mechanisms, focusing on the advantages and limitations of different sensing methods. Then, we highlight the recent advances in representative examples of visual ECL analysis, including aptasensing, multiplex immunoassays, cell imaging and single-particle analysis. At last, the outlook and prospects for the future visual ECL analysis are discussed based on the current development of ECL research.

Electrochemiluminescence Imaging Techniques for Analysis and Visualizing

Electrochemiluminescence (ECL)-based imaging analysis is a dominant method to inspect the electrode composition, to study electrochemical reaction kinetics at a microscopic level, and also a rapid emerging technology in bioanalysis with high spatiotemporal resolutions, high-throughput and visualization characteristics. In comparison with other imaging microscopes, an optical excitation is not involved in imaging, thus the approach is free from background noise resulting in a low detection limit. In this review work, the principle of ECL, its unique natures compared to other luminescence techniques were briefed at first. Then after, the progress and basic principles of ECL imaging were summarized. Furthermore, recent and representative advances of ECL imaging for visualizing and sensing applications were reviewed. Finally, the perspectives in ECL imaging for further perspective were discussed.

Electrochemiluminescence Biosensor for Nucleolin Imaging in a Single Tumor Cell Combined with Synergetic Therapy of Tumor.

Nucleolin, a nuclear biological multifunctional protein, plays significant roles in modulating the proliferation, survival, and apoptosis of tumor cells. Different from the traditional electrochemiluminescence (ECL) method, a new ECL biosensor was built to perform ECL imaging of nucleolin in a single HeLa cell with high sensitivity and throughput. Briefly, mesoporous silica nanoparticles (MSN) loaded with doxorubicin (DOX) and phorbol 12-myristate 13-acetate (PMA) were used as drug carriers and could be specifically opened by nucleolin in a HeLa cell. PMA then induced the HeLa cell to produce reactive oxygen species (ROS) and realized ECL imaging of nucleolin. After that, ROS could damage DNA and proteins of the tumor cell and DOX could induce the apoptosis of HeLa cells by inhibiting genetic material, nucleic acid, synthesis. HeLa cells were then efficiently killed by DOX and ROS in a synergetic pathway. Herein, a new ECL biosensor for ECL imaging of nucleolin in a single HeLa cell and synergetic tumor therapy was built.

Data-Driven Modeling of Smartphone-Based Electrochemiluminescence Sensor Data Using Artificial Intelligence.

Understanding relationships among multimodal data extracted from a smartphone-based electrochemiluminescence (ECL) sensor is crucial for the development of low-cost point-of-care diagnostic devices. In this work, artificial intelligence (AI) algorithms such as random forest (RF) and feedforward neural network (FNN) are used to quantitatively investigate the relationships between the concentration of luminophore and its experimentally measured ECL and electrochemical data. A smartphone-based ECL sensor with /TPrA was developed using disposable screen-printed carbon electrodes. ECL images and amperograms were simultaneously obtained following 1.2-V voltage application. These multimodal data were analyzed by RF and FNN algorithms, which allowed the prediction of concentration using multiple key features. High correlation (0.99 and 0.96 for RF and FNN, respectively) between actual and predicted values was achieved in the detection range between 0.02 µM and 2.5 µM. The AI approaches using RF and FNN were capable of directly inferring the concentration of using easily observable key features. The results demonstrate that data-driven AI algorithms are effective in analyzing the multimodal ECL sensor data. Therefore, these AI algorithms can be an essential part of the modeling arsenal with successful application in ECL sensor data modeling.

A novel l-cysteine regulated polydopamine nanoparticle-based electrochemiluminescence image application

In this work, novel l-cysteine regulated polydopamine nanoparticles (PDAcp NPs) with excellent electrochemiluminescence (ECL) behavior were synthesized.

Pore Confinement-Enhanced Electrochemiluminescence on SnO2 Nanocrystal Xerogel with NO3- As Co-Reactant and Its Application in Facile and Sensitive Bioanalysis.

Herein, 10-fold electrochemiluminescence (ECL) enhancement from a porous SnO2 nanocrystal (SnO2 NC) xerogel (vs discrete SnO2 NCs) was first observed with NO3- as a novel coreactant. This new booster phenomenon caused by pore characteristic was defined as "pore confinement-induced ECL enhancement", which originated from two possible reasons: First, the SnO2 NC xerogel with hierarchically porous structure could not only localize massive luminophore near the electrode surface, more importantly, but could accelerate the electrochemical and chemiluminescence reaction efficiency because the pore channels of xerogel could promote the mass transport and electron transfer in the confined spaces. Second, the NO3- could be in situ reduced easily to the active nitrogen species by means of the pore confinement effect, which could be served as a new coreactant for nanocrystal-based ECL amplification with the excellent stability and good biocompatibility. As a proof of concept, a facile and sensitive sensing platform for SO32- detection has been successfully constructed upon effectively quenching of SO32- toward the SnO2 NC xerogel/NO3- ECL system. The key feature about this work presented a grand avenue to achieve the strong ECL signal, especially from weak emitters, which gave a fresh impetus to the construction of new-generation of surface-confined ECL platform with potential applications in ECL imaging and sensing.

Perturbation Electrochemiluminescence Imaging to Observe the Fluctuation of Charge-Transfer Resistance in Individual Graphene Microsheets with Redox-Induced Defects.

Here, the fluctuation of charge-transfer resistance in individual reduced graphene oxide (rGO) microsheets with more redox-induced defects is unprecedentedly visualized using a perturbation electrochemiluminescence (ECL) imaging. This perturbation uses a short and low potential to recover defect-covered rGO microsheets slightly and then introduces a high potential to form more redox-induced defects resulting in an increase of charge-transfer resistance. Also, these defects at rGO microsheets enhance their catalytic feature and the resultant ECL intensity so that the temporal resolution in ECL imaging is improved to 30 ms. Aided by this fast imaging approach, the exponential decrease of ECL intensity at individual graphene microsheets after the oxidation is observed, which reflects the increase of their charge-transfer resistances. Since the charge-transfer resistance at electrode surfaces is mainly affected by the conductivity of electrode materials, the result provides the dynamic information to support the reduction of the electrical conductivity in graphene with more defects.

Quantifying Concentration Distribution in an Organic Redox Flow Battery Using in-Plane Neutron Radiography

Redox flow batteries (RFBs) are promising rechargeable electrochemical devices for grid-scale energy storage, but further cost reductions are needed for ubiquitous adoption of this technology [1]. While recent research trends have focused on molecular discovery [2], advances in the science and engineering of electrochemical reactors can lead to cost reductions via increased power density and/or decreased component cost. Key to such efforts is deconvolution of coupled transport and kinetic processes within operating device and, to this end, imaging diagnostics, such as X-ray tomographic microscopy [3], infrared thermography [4], and electrochemiluminescence imaging [5], have been employed to visualize relevant properties (e.g., fluid distribution, temperature) in RFBs. However, obtaining quantitative property descriptions at high resolution and under representative operation conditions remains a challenge. In this presentation, we introduce neutron radiography as an operando characterization method for RFBs which is particularly sensitivity to organic materials with high hydrogen content. To demonstrate the potential of this diagnostic tool, we characterize active species concentration distribution within a redox flow cell in a single electrolyte configuration with a nonaqueous electrolyte containing TEMPO/TEMPO+. We use subtractive neutron imaging [6] in combination with isotropic labelling to deconvolute the concentration of different electrolyte materials (i.e. supporting salts, active species). To resolve the concentration profiles across the different layers, we employ the in-plane imaging configuration [7] and correlate these profiles to cell performance via polarization and electrochemical impedance spectroscopy. References Darling et al., Energy & Environmental Science, 7, 3459 (2014).A. Kowalski et al., Current Opinion in Chemical Engineering, 13, 45 (2016).Tariq et al., Sustainable Energy & Fuels, 2, 2068 (2018).Tanaka et al., Journal of Energy Storage, 19, 67 (2018).Rubio-Garcia et al., Electrochemistry Communications, 93, 128 (2018).Boillat et al., Journal of The Electrochemical Society, 162(6), F531 (2015).Boillat et al., Electrochemistry Communications, 10(4), 546 (2008). Acknowledgments We gratefully acknowledge the financial support of the Swiss National Science Foundation (P2EZP2_172183) and the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the United States Department of Energy.

Neutron Imaging as a Method for Quantifying Concentration Distribution within an Organic Redox Flow Battery

Redox flow batteries (RFBs) are promising rechargeable electrochemical devices for grid-scale energy storage, but further cost reductions are needed for ubiquitous adoption of this technology [1]. While recent research trends have focused on molecular discovery [2], advances in the science and engineering of electrochemical reactors can lead to cost reductions via increased power density and/or decreased component cost. Key to such efforts is deconvolution of coupled transport and kinetic processes within operating device and, to this end, imaging diagnostics, such as X-ray tomographic microscopy [3], infrared thermography [4], and electrochemiluminescence imaging [5], have been employed to visualize relevant properties (e.g., fluid distribution, temperature) in RFBs. However, obtaining quantitative property descriptions at high resolution and under representative operation conditions remains a challenge. In this presentation, we introduce neutron radiography as an operando characterization method for RFBs which is particularly sensitivity to organic materials with high hydrogen content. To demonstrate the potential of this diagnostic tool, we characterize active species concentration distribution within a redox flow cell in a single electrolyte configuration with a nonaqueous electrolyte containing TEMPO/TEMPO+. Specifically, we employ the in-plane imaging configuration [6] to visualize concentration gradients across the flow fields, electrodes, and membrane and to correlate these profiles to cell performance via polarization and electrochemical impedance spectroscopy. References Darling et al., Energy & Environmental Science, 7, 3459 (2014).A. Kowalski et al., Current Opinion in Chemical Engineering, 13, 45 (2016).Tariq et al., Sustainable Energy & Fuels, 2, 2068 (2018).Tanaka et al., Journal of Energy Storage, 19, 67 (2018).Rubio-Garcia et al., Electrochemistry Communications, 93, 128 (2018).Boillat et al., Electrochemistry Communications, 10(4), 546 (2008). Acknowledgments We gratefully acknowledge the financial support of the Swiss National Science Foundation (P2EZP2_172183) and the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the United States Department of Energy.

Enhanced Bipolar Electrochemistry at Solid-State Micropores: Demonstration by Wireless Electrochemiluminescence Imaging.

Bipolar electrochemistry (BPE) is a powerful method based on the wireless polarization of a conductive object that induces the asymmetric electroactivity at its two extremities. A key physical limitation of BPE is the size of the conductive object because the shorter the object, the larger is the potential necessary for sufficient polarization. Micrometric and nanometric objects are thus extremely difficult to address by BPE due to the very high potentials required, in the order of tens of kV or more. Herein, the synergetic actions of BPE and of planar micropores integrated in a microfluidic device lead to the spatial confinement of the potential drop at the level of the solid-state micropore, and thus to a locally enhanced polarization of a bipolar electrode. Electrochemiluminescence (ECL) is emitted in half of the electroactive micropore and reveals the asymmetric polarization in this spatial restriction. Micrometric deoxidized silicon electrodes located in the micropore are polarized at a very low potential (7 V), which is more than 2 orders of magnitude lower compared to the classic bipolar configurations. This behavior is intrinsically associated with the unique properties of the micropores, where the sharp potential drop is focused. The presented approach offers exciting perspectives for BPE of micro/nano-objects, such as dynamic BPE with objects passing through the pores or wireless ECL-emitting micropores.

Recent advances in electrochemiluminescence imaging analysis based on nanomaterials and micro-/nanostructures

Electrochemiluminescence (ECL) is a kind of luminescent phenomenon caused by electrochemical reactions. Based on the advantages of ECL including low background, high sensitivity, strong spatiotemporal controllability and simple operation, ECL imaging is able to visualize the ECL process, which can additionally achieve high throughput, fast and visual analysis. With the development of optical imaging technique, ECL imaging at micro- or nanoscale has been successfully applied in immunoassay, cell imaging, biochemical analysis, single-nanoparticle detection and study of mechanisms and kinetics of reactions, which has attracted extensive attention. In this review, the basic principles and apparatus of ECL imaging were briefly introduced at first. Then several latest and representative applications of ECL imaging based on nanomaterials and micro-/nanostructures were overviewed. Finally, the superiorities and challenges in ECL imaging for further development were discussed.

In Situ Imaging Facet-Induced Spatial Heterogeneity of Electrocatalytic Reaction Activity at the Subparticle Level via Electrochemiluminescence Microscopy.

Investigating catalytic behavior of heterogeneous catalysts, especially at the crystal facets level, is crucial for rational catalyst design in the energy and environmental fields. Here we demonstrate an efficient approach to in situ visualize and analyze the heterogeneity of electrocatalytic activity on different facets at the subparticle level via electrochemiluminescence (ECL) microscopy. ZnO crystals with various exposed facet proportions were synthesized, and the correlation between their electrocatalytic performance toward luminol analogue degradation and the exposed facets is established. It is clearly imaged that the ZnO (002) facet has superior catalytic performance compared to the ZnO (100) facet, which is supported by theoretical computation and electrochemical experiments as the facet-induced heterogeneity of the catalytic effect on oxygen reduction into the key reactant for ECL. Accordingly, the spatial heterogeneity of electrocatalytic activity at different facets on one particle is visualized for the first time. The realization of subparticle ECL imaging and kinetic analysis could provide a special approach to visualize facet-induced spatial heterogeneity of catalytic behavior and valuable information for the catalysis study and analysis.

Potential-Resolved Electrochemiluminescence Nanoprobes for Visual Apoptosis Evaluation at Single-Cell Level.

In this work, a potential-resolved electrochemiluminescence (ECL) method is developed and used for the apoptosis diagnosis at the single-cell level. The apoptosis of cells usually induces the decreasing expression of epidermal growth factor receptor (EGFR) and promotes phosphatidylserine (PS) eversion onthe cell membrane. Here, Au@L012 and g-C3N4 as ECL probes are functionalized with epidermal growth factor (EGF) and peptide (PSBP) to recognize the EGFR and PS on the cell surface, respectively, showing two well-separated ECL signals during a potential scanning. Experimental results reveal that the relative ECL change of g-C3N4 and Au@L012 correlates with the degree of apoptosis, which provides an accurate way to investigate apoptosis without interference that solely changes EGFR or PS. With a homemade ECL microscopy, we simultaneously evaluate the EGFR and PS expression of abundant individual cells and, therefore, achieve the visualization analysis of the apoptosis rate for normal and cancer cell samples. This strategy contributes to visually studying tumor markers and pushing the application of ECL imaging for the disease diagnosis at the single-cell level.