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We describe the elaboration of a multiscale-tailored bioelectrocatalytic system. The combination of two enzymes, D-sorbitol dehydrogenase and diaphorase, is studied with respect to the oxidation of D-sorbitol as a model system. The biomolecules are immobilized in an electrodeposited paint (EDP) layer. Reproducible and efficient catalysis of D-sorbitol oxidation is recorded when this system is immobilized on a gold electrode modified by a self-assembled monolayer of 4-carboxy-(2,5,7-trinitro-9-fluorenylidene)malonitrile used as a mediator. The insertion of mediator-modified gold nanoparticles into the EDP film increases significantly the active surface area for the catalytic reaction, which can be further enhanced when the whole system is immobilized in macroporous gold electrodes. This multiscale architecture finally leads to a catalytic device with optimized efficiency for potential use in biosensors, bioelectrosynthesis, and biofuel cells., (© 2011 American Chemical Society)

Bipolar electrochemistry (BE) combined with electrochemiluminescence (ECL) has gained considerable attention as a versatile and powerful analytical technique operating in a wireless manner. However, only co‐reactant ECL has been reported so far when using a BE setup. In this work, the generation of annihilation ECL at the anodic extremity of a bipolar electrode (BPE) is demonstrated in two different spatial arrangements of the electrodes. The reported approach is based on a synergetic effect between the asymmetric electroactivity induced across the BPE, which produces different redox states of [Ru(bpy)3]2+, and the electro‐migration mechanism of the formed ionic species, allowing the localization and concentration of the ECL emission. The presented approach demonstrating annihilation ECL via BE, paves the way for the design of easy and straightforward light‐emitting platforms for multiple applications. [ABSTRACT FROM AUTHOR]

Water splitting has become a sustainable and clean alternative for hydrogen production. Commonly, the efficiency of such reactions is intimately related to the physico‐chemical properties of the catalysts that constitute the electrolyzer. Thus, the development of simple and fast methods to evaluate the electrocatalytic efficiency of an electrolyzer is highly required. In this work, we present an unconventional method based on the combination of bipolar electrochemistry and light‐emitting diodes, which allows the evaluation of the electrocatalytic performance of the two types of catalysts, composing an electrolyzer, namely for oxygen and hydrogen evolution reactions, respectively. The integrated light emission of the diode acts as an optical readout of the electrocatalytic information, which simultaneously depends on the composition of the anode and the cathode. The electrocatalytic activity of Au, Pt, and Ni electrodes, connected to the LED in multiple anode/cathode configurations, towards the water splitting reactions has been evaluated. The efficiency of the electrolyzer can be represented in terms of the onset electric field (ϵonset) for light emission, obtaining variations that are in agreement with data reported with conventional electrochemistry. This work introduces a straightforward method for evaluating electrocatalysts and underscores the importance of material characterization in developing efficient electrolyzers for hydrogen production. [ABSTRACT FROM AUTHOR]

The development of chiral catalysts plays a very important role in various areas of chemical science. Heterogeneous catalysts have the general advantage of allowing a more straightforward separation from the products. One specific case of heterogeneous catalysis is electrocatalysis, being potentially a green chemistry approach. However, a typical drawback is that the redox conversion of molecules occurs only at the electrode/electrolyte interface, and not in the bulk of the electrolyte. The second limitation is that the electrodes have to be physically connected to a power supply to induce the desired reactions. To circumvent these problems, we propose here a complementary approach by replacing macroscopic electrodes with an ensemble of self‐propelled redox active microswimmers. They move autonomously in solution while transforming simultaneously a prochiral starting compound into a specific enantiomer with a very high enantiomeric excess, accompanied by a significantly increased production rate of the favorite enantiomer. [ABSTRACT FROM AUTHOR]

This article, titled "Cover Feature: Wireless Light-Emitting Electrode Arrays for the Evaluation of Electrocatalytic Activity," discusses a new method for visualizing the catalytic activity of electrode materials using light-emitting diodes (LEDs). The system, integrated into a bipolar electrochemical set-up, allows for the evaluation of the efficiency of anodic and cathodic catalysts for water splitting in a single image. This optical readout of catalytic information is complementary to traditional electrochemical techniques. The article provides more information on this research, conducted by A. Kuhn, G. Salinas, and their colleagues. [Extracted from the article]

The immobilization of bilirubin oxidase (BOD) on macroporous gold electrodes for the optimization of bioelectrocatalytic activity is described. A bilirubin oxidase mutant S362C (cys‐BOD) engineered with a cysteine residue located on purpose at the enzyme surface close to the T1 active center was used. It allows the attachment in one‐step of a self‐assembled monolayer of the enzyme to gold through a reaction between the thiol group of the cysteine residue and the metal surface. BOD immobilization of wild type and S362C mutant in macroporous gold electrodes allowed high retention of activity and perfect control of the overall BOD loading due to the fine‐tuning of the macroporous structure. The macroporous arrangement together with the use of cys‐BOD makes these rationally designed enzyme‐modified electrodes very promising candidates for high‐performance bioelectrocatalytic devices with improved activity and stability. [ABSTRACT FROM AUTHOR]

This article reports on a procedure to predict the optimal thickness of cylindrical porous electrodes operating a single redox reaction. This is obtained from a macroscopic model for the coupled diffusion‐reaction process that is first validated with voltammetry experiments of the H2O2/H2O reduction reaction carried out with a series of porous electrodes elaborated in this work. An analytical solution to this model is developed in the steady regime and for electrodes featuring a thickness to mean radius ratio small enough compared to unity. An analytical expression of the optimal electrode thickness is derived corresponding to the crossover value of two asymptotic regimes characterizing the dependence of the volume current density produced by the electrode upon its thickness. The predictive tool of the optimal thickness is general, regardless of the porous microstructure. The case of the electrodes used in the reported experiments illustrates that the optimal thickness is not intrinsic to the microsctructure characterized by the size of the representative volume, its specific area and effective diffusion coefficient. It also depends on the operating conditions reflected in the kinetic number, Ki, and the thickness of the diffusion layer surrounding the electrode. The dependence of the optimal thickness on these two parameters is quite significant in a range of very small values of Ki but remains quasi constant beyond a threshold value. A macroscale model for diffusion and single redox reactions in a porous electrode is recalled and validated experimentally. The analytical solution is obtained at steady‐state for a cylindrical electrode featuring a thickness to mean radius ratio small compared to unity. Given the microstructure of the electrode material, the optimal thickness (Le*op) of the cylindrical electrode is obtained from an analytical formula showing the dependence of Le*op on the kinetic number and diffusion layer thickness. [ABSTRACT FROM AUTHOR]

The preparation of surface gradients is a hot topic in contemporary research. Among various physical chemistry approaches, bipolar electrochemistry allows the control of such gradients through the interfacial polarization between a conducting substrate and an electrolyte solution. Here, we report the straightforward, single-step generation of metal composition gradients on cylindrical carbon fibers. The screening of different metal deposit morphologies, which evolve gradually along a bipolar electrode, is demonstrated with monometallic layers as well as a bimetallic composite layer based on copper and nickel. [ABSTRACT FROM AUTHOR]

We are developing a cell-based bioelectronic glucose sensor that exploits the multi-parametric sensing ability of pancreatic islet cells for the treatment of diabetes. These cells sense changes in the concentration of glucose and physiological hormones and immediately react by generating electrical signals. In our sensor, signals from multiple cells are recorded as field potentials by a micro-electrode array (MEA). Thus, cell response to various factors can be assessed rapidly and with high throughput. However, signal quality and consequently overall sensor performance rely critically on close cell–electrode proximity. Therefore, we present here a non-invasive method of further exploiting the electrical properties of these cells to guide them towards multiple micro-electrodes via electrophoresis. Parameters were optimized by measuring the cell's zeta potential and modeling the electric field distribution. Clonal and primary mouse or human β-cells migrated directly to target electrodes during the application of a 1 V potential between MEA electrodes for 3 minutes. The morphology, insulin secretion, and electrophysiological characteristics were not altered compared to controls. Thus, cell manipulation on standard MEAs was achieved without introducing any external components and while maintaining the performance of the biosensor. Since the analysis of the cells' electrical activity was performed in real time via on-chip recording and processing, this work demonstrates that our biosensor is operational from the first step of electrically guiding cells to the final step of automatic recognition. Our favorable results with pancreatic islets, which are highly sensitive and fragile cells, are encouraging for the extension of this technique to other cell types and microarray devices. [ABSTRACT FROM AUTHOR]

Chiral imprinted mesoporous platinum was electrochemically synthesized in the presence of mandelic acid and Brij 56 surfactant as chiral and mesoporous templates, respectively. The chiral cavity obtained by using mandelic acid as a template can be used to distinguish between enantiomers of other chiral molecules in which the stereocentre has a correlated configuration with respect to the imprinted one. This recognition versatility was tested for the discrimination of DOPA enantiomers. Mesoporous platinum electrodes imprinted with ( R)-mandelic acid preferentially react with L-DOPA and vice versa for the ( S)-mandelic acid imprinted one, which is more reactive for D-DOPA. [ABSTRACT FROM AUTHOR]

Bipolar electrochemistry is a technique with a rather young history in the field of analytical chemistry. Being based on the polarization of a conducting object which is exposed to an external electric field, it allowed recently the development of new methods for controlled surface modification at the micro- and nanoscale and very original analytical applications. Using bipolar electrodes, analyte separation and detection becomes possible based on miniaturized systems. Moreover, the modified objects that can be created with bipolar electrochemistry could find applications as key components for detection systems. In this contribution, the principles of bipolar electrochemistry will be reviewed, as well as recent developments that focus on the modification of objects at the nano- and microscale and their potential application in miniaturized analytical systems. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Cover Feature: Rational Design of Enzyme-Modified Electrodes for Optimized Bioelectrocatalytic Activity (ChemElectroChem 19/2019) Keywords: bilirubin oxidase; cysteine; enzyme engineering; direct electron transfer; macroporous electrodes; bioelectrocatalysis Bilirubin oxidase, cysteine, enzyme engineering, direct electron transfer, macroporous electrodes, bioelectrocatalysis. [Extracted from the article]

The article focuses on bipolar electrochemistry which is a phenomenon based on the polarization of conducting objects in electric fields. It mentions that the oxidation and reduction reactions of bipolar electrochemistry occur simultaneously on the same electrode. It outlines several factors to consider when using bipolar electrochemistry in developing scientific approaches.

Bulk electrocatalytic NADH regeneration is achieved on MOF functionalized microelectrodes via bipolar electrochemistry. This wireless approach allows in situ transformation of pyruvate into L-lactate with the highest Turn-Over-Frequency reported so far for a non-enzymatic catalyst system, opening up promising perspectives for employing this concept also for various other electroenzymatic bulk processes. [Display omitted] • Bulk electroenzymatic catalysis is carried out on MOF modified microparticles. • Bipolar electrochemistry allows in situ transformation of pyruvate into L-lactate as a model system. • Highest Turn-Over-Frequency reported so far for a non-enzymatic catalyst system. • This wireless bioelectrocatalytic concept can be generalized for a variety of other enzymes. Electrochemical regeneration of the cofactor nicotinamide adenine dinucleotide (NADH) is crucial for the enzymatic synthesis of a variety of valuable chemicals. [Rh(Cp*)(bpy)Cl]+ has been reported as one of the most efficient non-enzymatic catalysts for electrochemical regeneration of NADH, but the efficiency of the existing systems is still far from satisfying. Here we propose to suspend metal–organic framework functionalized glassy carbon beads in a bipolar electrochemical cell under mechanical stirring for bulk electroenzymatic synthesis. The beads are modified with a metal–organic framework NU-1000 shell, in which [Rh(Cp*)(bpy)Cl]+ catalyst is incorporated via the solvent-assisted ligand incorporation approach. Enzymatically active 1,4-NADH is electrochemically regenerated, and finally bipolar electrochemical bulk conversion of pyruvate into L-lactate is performed in the presence of NADH dependent L-lactate dehydrogenase as a model system. The very high turnover frequency (TOF) of 3100 ± 106 h−1 opens up promising perspectives for employing this concept also for various other electroenzymatic bulk processes. [ABSTRACT FROM AUTHOR]

Abstract: We report on the elaboration of macroporous antimony film electrodes. The strategy to create macroporous electrodes is based on the replication of colloidal crystal templates. These electrodes of controlled porosity show an increased internal electroactive area and a significantly improved electrochemical performance. The application of this novel electrochemical sensor for the sensitive quantification of traces of heavy metals has been demonstrated in combination with differential pulse anodic stripping voltammetry in model solutions. [Copyright &y& Elsevier]

Here we describe a new aspect of multicolor potential-resolved electrochemiluminescence (ECL) based on bipolar electrochemistry (BPE). BPE involves a potential gradient established along a polarized conducting object which thus acts as a bipolar electrode (BE). The resulting driving force can induce electron-transfer reactions, necessary for processes such as ECL occurring at different longitudinal locations along the same BE. In this work, we exploit the entire spatial domain where anodic polarization occurs to demonstrate, for the first time, how the potential gradient along a BE may be used to simultaneously resolve the emissions of ECL-active luminophores with differing oxidation potentials. The control of both size and position of the ECL-emitting domains was achieved by tuning the applied electric field. Multicolor light-emission was analyzed in detail to demonstrate spatial and spectral resolution of a solution containing different emitters. [ABSTRACT FROM AUTHOR]

In this contribution, a wireless method for the electrolytic sampling of heavy metals at special bismuth-modified particles is presented. For the first time, glassy carbon beads were asymmetrically modified with bismuth using bipolar electrochemistry. The resulting chemically asymmetric beads, so-called Janus particles, could be employed for the wireless electroaccumulation of heavy metal ions in the bismuth film. The qualitative and quantitative aspects of this concept have been studied by using anodic stripping voltammetry with Cd2+ and Pb2+ as the model ions. Different experimental and instrumental parameters have been optimized; among others, the concentration of Bi3+ ions, the deposition conditions for the bismuth-film, and the accumulation time of the target heavy metals. The developed concept could be applied to the transfer of heavy metal ions from a solution into a confined space without need to electrically connect the collector (electrode), thus representing an interesting new approach for trace metal analysis in small volumes. [ABSTRACT FROM AUTHOR]

Abstract: Electro-assisted generation of ultra-thin silica films can be achieved by using very dilute tetraethoxysilane (TEOS) precursors in the starting sol. The electrochemical manipulation of pH enables to catalyze polycondensation only at the electrode/solution interface, which offers the advantage of uniform deposition of thin layers onto the whole internal surfaces of macroporous gold electrodes, without any pore clogging effect. This opens promising avenues for application in various fields, as shown here for active biomolecule encapsulation. [Copyright &y& Elsevier]

Abstract: Porous electrodes with increased surface area have been prepared using a template route via colloidal crystals. The ordered porous structure and the interconnections between the pores have been quantitatively characterized by Focused Ion Beam Tomography. The internal surfaces of the electrodes have been biofunctionalized with two enzymatic systems for glucose oxidation. In order to increase significantly the stability, the biocatalysts have been immobilized either by crosslinking or by incorporation in an electrodeposition paint. The modified porous electrodes show an increased overall signal and therefore a better detection limit and a higher sensitivity when used as sensors, and a potentially higher power output when employed in biofuel cells. [Copyright &y& Elsevier]

Recent work on the preparation of highly organized macroporous electrodes and nanoporous ultramicroelectrodes has been combined and extended to elaborate macroporous ultramicroelectrodes (UMEs) by template synthesis using colloidal crystals and following two different and complementary methods. On the one hand, arched porous UMEs were prepared, and on the other hand, cylindrical porous UMEs were obtained by using cavity UMEs. These macroporous UMEs have an active surface area which is up to 2 orders of magnitude higher compared to that of a classical disk UME as characterized by cyclic voltammetry. To study their analytical performance, the macroporous UMEs have been modified with a redox-active thiol and also a model bioelectrocatalytical system containing a redox mediator, a cofactor, and glucose-dehydrogenase. In both cases the electrochemical signal is amplified by up to 2 orders of magnitude, which increases significantly the analytical performance of such electrodes and therefore opens up new applications for this kind of miniaturized electrochemical system. [ABSTRACT FROM AUTHOR]

Abstract: Macroporous gold electrodes are used in amperometric measurements as they provide a high internal surface area. Their cavities allow the sequential immobilisation of monolayers of redox mediator, coenzyme and dehydrogenase, leading to a well-defined electroactive multilayer. The highly ordered arrangement of the pores makes it possible to fine-tune the overall activity of the device. [Copyright &y& Elsevier]

For the first time the inner surface of highly organized macroporous electrodes, obtained by electrodeposition of gold into the interstitial spaces of a self-assembled close packed array of latex beads, is modified with a monolayer of a catalyst. The combination of the increased specific surface area of these electrodes and the high catalytic rate constant of the redox mediator allows us to construct surfaces showing good electrocatalytic efficiency. As a model system the electrooxidation of NADH using nitrofluorenone mediators is studied. [Copyright &y& Elsevier]