Complex electrochemiluminescence patterns shaped by hydrodynamics at a rotating bipolar electrode.

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.

Integrating environmental gradients into breeding: application of genomic reactions norms in a perennial species.

Global warming threatens the productivity of forest plantations. We propose here the integration of environmental information into a genomic evaluation scheme using individual reaction norms, to enable the quantification of resilience in forest tree improvement and conservation strategies in the coming decades. Random regression models were used to fit wood ring series, reflecting the longitudinal phenotypic plasticity of tree growth, according to various environmental gradients. The predictive ability of the models was considered to select the most relevant environmental gradient, namely a gradient derived from an ecophysiological model and combining trunk water potential and temperature. Even if the individual ranking was preserved over most of the environmental gradient, strong genotype x environment interactions were detected in the extreme unfavorable part of the gradient, which includes environmental conditions that are very likely to be more frequent in the future. Combining genomic information and longitudinal data allowed to predict the growth of individuals in environments where they have not been observed. Phenotyping of 50% of the individuals in all the environments studied allowed to predict the growth of the remaining 50% of individuals in all these environments with a predictive ability of 0.25. Without changing the total number of observations, adding observations in a reduced number of environments for the individuals to be predicted, while decreasing the number of individuals phenotyped in all environments, increased the predictive ability to 0.59, highlighting the importance of phenotypic data allocation. We found that genomic reaction norms are useful for the characterization and prediction of the function of genetic parameters and facilitate breeding in a climate change context.

Wireless Multimodal Light-Emitting Arrays Operating on the Principles of LEDs and ECL.

Electrochemistry-based light-emitting devices have gained considerable attention in different applications such as sensing and optical imaging. In particular, such systems are an interesting alternative for the development of multimodal light-emitting platforms. Herein we designed a multicolor light-emitting array, based on the electrochemical switch-on of light-emitting diodes (LEDs) with a different intrinsic threshold voltage. Thermodynamically and kinetically favored coupled redox reactions, i. e. the oxidation of Mg and the reduction of protons on Pt, act as driving force to power the diodes. Moreover, this system enables to trigger an additional light emission based on the interfacial reductive-oxidation electrochemiluminescence (ECL) mechanism of the Ru(bpy)3 2+/S2O8 2- system. The synergy between these light-emission pathways offers a multimodal platform for the straightforward optical readout of physico-chemical information based on composition changes of the solution.

Wireless rotating bipolar electrochemiluminescence for enzymatic detection.

New dynamic, wireless and cost-effective analytical devices are developing rapidly in biochemical analysis. Here, we report on a remotely-controlled rotating electrochemiluminescence (ECL) sensing system for enzymatic detection of a model analyte, glucose, on both polarized sides of an iron wire acting as a bipolar electrode. The iron wire is controlled by double contactless mode, involving remote electric field polarization, and magnetic field-induced rotational motion. The former triggers the interfacial polarization of both extremities of the wire by bipolar electrochemistry, which generates ECL emission of the luminol derivative (L-012) with the enzymatically produced hydrogen peroxide in presence of glucose, at both anodic and cathodic poles, simultaneously. The latter generates a convective flow, leading to an increase in mass transfer and amplifying the corresponding ECL signals. Quantitative glucose detection in human serum samples is achieved. The ECL signals were found to be a linear function of the glucose concentration within the range of 10-1000 µM and with a limit of detection of 10 µM. The dynamic bipolar ECL system simultaneously generates light emissions at both anodic and cathodic poles for glucose detection, which can be further applied to biosensing and imaging in autonomous devices.

Modulation of circularly polarized luminescence by swelling of microgels functionalized with enantiopure [Ru(bpy)3]2+ luminophores.

Chemoresponsive microgels functionalized with enantiomeric Δ- or Λ-[Ru(bpy)3]2+ showed tunable chiroptical properties upon swelling and shrinking. The tuning is triggered by a modulation of the local mobility of [Ru(bpy)3]2+ upon addition of fructose, controlling interactions and distances between [Ru(bpy)3]2+ and phenylboronic acid.

Wireless Magnetoelectrochemical Induction of Rotational Motion.

Electromagnetically induced rotation is a key process of many technological systems that are used in daily life, especially for energy conversion. In this context, the Lorentz force-induced deviation of charges is a crucial physical phenomenon to generate rotation. Herein, they combine the latter with the concept of bipolar electrochemistry to design a wireless magnetoelectrochemical rotor. Such a device can be considered as a wet analog of a conventional electric motor. The main driving force that propels this actuator is the result of the synergy between the charge-compensating ion flux along a bipolar electrode and an external magnetic field applied orthogonally to the surface of the object. The trajectory of the wirelessly polarized rotor can be controlled by the orientation of the magnetic field relative to the direction of the global electric field, producing a predictable clockwise or anticlockwise motion. Fine-tuning of the applied electric field allows for addressing conducting objects having variable characteristic lengths.

Tris(2,2'-bipyridyl)ruthenium (II) complex as a universal reagent for the fabrication of heterogeneous electrochemiluminescence platforms and its recent analytical applications.

In recent years, electrochemiluminescence (ECL) has received enormous attention and has emerged as one of the most successful tools in the field of analytical science. Compared with homogeneous ECL, the heterogeneous (or solid-state) ECL has enhanced the rate of the electron transfer kinetics and offers rapid response time, which is highly beneficial in point-of-care and clinical applications. In ECL, the luminophore is the key element, which dictates the overall performance of the ECL-based sensors in various analytical applications. Tris(2,2'-bipyridyl)ruthenium (II) complex, Ru(bpy)32+, is a coordination compound, which is the gold-standard luminophore in ECL. It has played a key role in translating ECL from a "laboratory curiosity" to a commercial analytical instrument for diagnosis. The aim of the present review is to provide the principles of ECL and classical reaction mechanisms-particularly involving the heterogeneous Ru(bpy)32+/co-reactant ECL systems, as well as the fabrication methods and its importance over solution-phase Ru(bpy)32+ ECL. Then, we discussed the emerging technology in solid-state Ru(bpy)32+ ECL-sensing platforms and their recent potential analytical applications such as in immunoassay sensors, DNA sensors, aptasensors, bio-imaging, latent fingerprint detection, point-of-care testing, and detection of non-biomolecules. Finally, we also briefly cover the recent advances in solid-state Ru(bpy)32+ ECL coupled with the hyphenated techniques.

Enzymatic cascade reaction in simple-coacervates.

The design of enzymatic droplet-sized reactors constitutes an important challenge with many potential applications such as medical diagnostics, water purification, bioengineering, or food industry. Coacervates, which are all-aqueous droplets, afford a simple model for the investigation of enzymatic cascade reaction since the reactions occur in all-aqueous media, which preserve the enzymes integrity. However, the question relative to how the sequestration and the proximity of enzymes within the coacervates might affect their activity remains open. Herein, we report the construction of enzymatic reactors exploiting the simple coacervation of ampholyte polymer chains, stabilized with agar. We demonstrate that these coacervates have the ability to sequester enzymes such as glucose oxidase and catalase and preserve their catalytic activity. The study is carried out by analyzing the color variation induced by the reduction of resazurin. Usually, phenoxazine molecules acting as electron acceptors are used to characterize glucose oxidase activity. Resazurin (pink) undergoes a first reduction to resorufin (salmon) and then to dihydroresorufin (transparent) in presence of glucose oxidase and glucose. We have observed that resorufin is partially regenerated in the presence of catalase, which demonstrates the enzymatic cascade reaction. Studying this enzymatic cascade reaction within coacervates as reactors provide new insights into the role of the proximity, confinement towards enzymatic activity.

Wireless electrochemical light emission in ultrathin 2D nanoconfinements.

Spatial confinement of chemical reactions or physical effects may lead to original phenomena and new properties. Here, the generation of electrochemiluminescence (ECL) in confined free-standing 2D spaces, exemplified by surfactant-based air bubbles is reported. For this, the ultrathin walls of the bubbles (typically in the range of 100-700 nm) are chosen as a host where graphene sheets, acting as bipolar ECL-emitting electrodes, are trapped and dispersed. The proposed system demonstrates that the required potential for the generation of ECL is up to three orders of magnitude smaller compared to conventional systems, due to the nanoconfinement of the potential drop. This proof-of-concept study demonstrates the key advantages of a 2D environment, allowing a wireless activation of ECL at rather low potentials, compatible with (bio)analytical systems.

Wireless Imaging of Transient Redox Activity Based on Bipolar Light-Emitting Electrode Arrays.

Bipolar electrochemistry (BE) is a wireless electrochemical technique, which enables asymmetric electroactivity on the surface of conducting objects. This technique has been extensively studied for different electrochemical applications, including synthesis, separation, sensing, and surface modification. Here, we employ BE for imaging the transient electrochemical activity of different redox species with high accuracy via an array of light-emitting diodes having different lengths. Such a gradient allows the differentiation of redox systems due to their intrinsic difference in thermodynamic potential and the evaluation of their diffusional behavior based on the intensity of light emission. The result is an instantaneous optical readout of analytical information, equivalent to classic electrochemical scanning techniques, such as linear sweep voltammetry.

Local pH Modulation during Electro-Enzymatic O2 Reduction: Characterization of the Influence of Ionic Strength by In Situ Fluorescence Microscopy.

Understanding how environmental factors affect the bioelectrode efficiency and stability is of uttermost importance to develop high-performance bioelectrochemical devices. By coupling fluorescence confocal microscopy in situ to electrochemistry, this work focuses on the influence of the ionic strength on electro-enzymatic catalysis. In this context, the 4 e-/4 H+ reduction of O2 into water by the bilirubin oxidase from Myrothecium verrucaria (MvBOD) is considered as a model. The effects of salt concentration on the enzyme activity and stability were probed by enzymatic assays performed in homogeneous catalysis conditions and monitored by UV-vis absorption spectroscopy. They were also investigated in heterogeneous catalysis conditions by electrochemical measurements with MvBOD immobilized at a graphite microelectrode. We demonstrate that the catalytic activity and stability of the enzyme both in solution and in the immobilized state at the bioelectrode were conserved with an electrolyte concentration of up to 0.5 M, both in a buffered and a non-buffered electrolyte. Relying on this, we used fluorescence confocal laser scanning microscopy coupled in situ to electrochemistry to explore the local pH of the electrolyte at the vicinity of the electrode surface at various ionic strengths and for several overpotentials. 3D proton depletion profiles generated by the interfacial electro-enzymatic reaction were recorded in the presence of a pH-sensitive fluorophore. These concentration profiles were shown to contract with increasing ionic strength, thus highlighting the need for a minimal electrolyte concentration to ensure availability of charged substrates at the electrode surface during electro-enzymatic experiments.

Electrochemiluminescence with semiconductor (nano)materials.

Electrochemiluminescence (ECL) is the light production triggered by reactions at the electrode surface. Its intrinsic features based on a dual electrochemical/photophysical nature have made it an attractive and powerful method across diverse fields in applied and fundamental research. Herein, we review the combination of ECL with semiconductor (SC) materials presenting various typical dimensions and structures, which has opened new uses of ECL and offered exciting opportunities for (bio)sensing and imaging. In particular, we highlight this particularly rich domain at the interface between photoelectrochemistry, SC material chemistry and analytical chemistry. After an introduction to the ECL and SC fundamentals, we gather the recent advances with representative examples of new strategies to generate ECL in original configurations. Indeed, bulk SC can be used as electrode materials with unusual ECL properties or light-addressable systems. At the nanoscale, the SC nanocrystals or quantum dots (QDs) constitute excellent bright ECL nano-emitters with tuneable emission wavelengths and remarkable stability. Finally, the challenges and future prospects are discussed for the design of new detection strategies in (bio)analytical chemistry, light-addressable systems, imaging or infrared devices.

Enhanced Cathodic Electrochemiluminescence of Luminol on Iron Electrodes.

Electrochemiluminescence (ECL) behavior of luminol derivative was investigated in reduction on different electrode materials. We found that luminol and its widely used L-012 derivative, emitting at physiological pH values, exhibit strong cathodic ECL emission on iron and stainless steel electrodes with hydrogen peroxide, whereas no ECL signal was observed with other classic electrode materials (Au, Pt, and C). On a Ni electrode, a low cathodic ECL signal was observed. This points out to the essential role of iron-containing materials to enhance the cathodic ECL emission. Under the reported conditions, the cathodic ECL signal of L-012 is comparable to the classically used anodic ECL emission. Thus, dual bright ECL emissions with L-012 were obtained simultaneously in oxidation and in reduction on iron materials as imaged in a wireless bipolar electrochemistry configuration. Such an ECL system generating light emission concomitantly in oxidation and in reduction is extremely rare and it opens appealing (bio)analytical and imaging applications, in biosensing, remote detection, bipolar ECL analysis, and ECL-based cell microscopy.

Lorentz Force-Driven Autonomous Janus Swimmers.

Autonomous swimmers have been intensively studied in recent years due to their numerous potential applications in many areas ranging from biomedicine to environmental remediation. Their motion is based either on different self-propulsion mechanisms or on the use of various external stimuli. Herein, the synergy between the ion flux around self-electrophoretic Mg/Pt Janus swimmers and an external magnetic field is proposed as an efficient alternative mechanism to power swimmers on the basis of the resulting Lorentz force. A strong magnetohydrodynamic effect is observed due to the orthogonal combination of magnetic field and spontaneous ionic currents, leading to an increase of the swimmer speed by up to 2 orders of magnitude. Furthermore, the trajectory of the self-propelled swimmers can be controlled by the orientation of the magnetic field, due to the presence of an additional torque force caused by a horizontal cation flux along the swimmer edges, resulting in predictable clockwise or anticlockwise motion. In addition, this effect is independent of the swimmer size, since a similar type of rotational motion is observed for macro- and microscale objects.

Bipolar (Bio)electroanalysis.

This contribution reviews a selection of the most recent studies on the use of bipolar electrochemistry in the framework of analytical chemistry. Despite the fact that the concept is not new, with several important studies dating back to the middle of the last century, completely novel and very original approaches have emerged over the last decade. This current revival illustrates that scientists still (re)discover some exciting virtues of this approach, which are useful in many different areas, especially for tackling analytical challenges in an unconventional way. In several cases, this "wireless" electrochemistry strategy enables carrying out measurements that are simply not possible with classic electrochemical approaches. This review will hopefully stimulate new ideas and trigger scientists to integrate some aspects of bipolar electrochemistry in their work in order to drive the topic into yet unexplored and eventually completely unexpected directions.

Near-infrared electrochemiluminescence in water through regioselective sulfonation of diaza [4] and [6]helicene dyes.

A series of water-soluble helicene dyes generating intense electrochemiluminescence (ECL) signal in physiological conditions is reported. Those species were prepared using diaza [4] and [6]helicenes as structural cores modified with sulfonate groups in various positions. Such groups improve their water solubility and can induce a red-shifted emission. Efficient ECL up to the near-infrared is achieved in water, demonstrating a viable strategy for the design of new near-infrared ECL dyes for bioassays and microscopy.

In Situ Fluorescence Tomography Enables a 3D Mapping of Enzymatic O2 Reduction at the Electrochemical Interface.

Getting information about the fate of immobilized enzymes and the evolution of their environment during turnover is a mandatory step toward bioelectrode optimization for effective use in biodevices. We demonstrate here the proof-of-principle visual characterization of the reactivity at an enzymatic electrode thanks to fluorescence confocal laser scanning microscopy (FCLSM) implemented in situ during the electrochemical experiment. The enzymatic O2 reduction involves proton-coupled electron transfers. Therefore, fluorescence variation of a pH-dependent fluorescent dye in the electrode vicinity enables reaction visualization. Simultaneous collection of electrochemical and fluorescence signals gives valuable space- and time-resolved information. Once the technical challenges of such a coupling are overcome, in situ FCLSM affords a unique way to explore reactivity at the electrode surface and in the electrolyte volume. Unexpected features are observed, especially the pH evolution of the enzyme environment, which is also indicated by a characteristic concentration profile within the diffusion layer. This coupled approach also gives access to a cartography of the electrode surface response (i.e., heterogeneity), which cannot be obtained solely by an electrochemical means.

Chiroptical detection of a model ruthenium dye in water by circularly polarized-electrochemiluminescence.

We demonstrate the possibility to detect selectively the two single enantiomers of a model [Ru(bpy)3]2+-based dye by circularly polarized-electrochemiluminescence (CP-ECL). This new aspect of the ECL emission combines the chiral information intrinsic to CPL methods with an electrogeneration of the excited state. Thus, it opens the possibility to perform ECL-based bioassays or microscopy with efficient chiral dyes.

Chemo- and Magnetotaxis of Self-Propelled Light-Emitting Chemo-electronic Swimmers.

Miniaturized autonomous chemo-electronic swimmers, based on the coupling of spontaneous oxidation and reduction reactions at the two poles of light-emitting diodes (LEDs), are presented as chemotactic and magnetotactic devices. In homogeneous aqueous media, random motion caused by a bubble-induced propulsion mechanism is observed. However, in an inhomogeneous environment, the self-propelled devices exhibit positive chemotactic behavior, propelling themselves along a pH or ionic strength gradient (∇pH and ∇I, respectively) in order to reach a thermodynamically higher active state. In addition, the intrinsic permanent magnetic moment of the LED allows self-orientation in the terrestrial magnetic field or following other external magnetic perturbations, which enables a directional motion control coupled with light emission. The interplay between chemotaxis and magnetotaxis allows fine-tuning of the dynamic behavior of these swimmers.