Control of Interfacial Potentials and Redox Reactions on Bipolar Electrodes Using Ag/AgCl

The interfacial potential difference on the surface of bipolar electrodes was controlled by placing Ag/AgCl on part of the electrode. Oxygen reduction on the cathodic pole was coupled with an electrochemiluminescence (ECL) reaction on the anodic pole. In an open bipolar system, the ECL intensity depended on the location of Ag/AgCl and the concentration of Cl⁻ ions. A current flowed through Ag/AgCl and the ratio of currents generated at the anodic and cathodic poles was affected by the position of Ag/AgCl. Further, the effect of Ag/AgCl placement was also demonstrated in a closed bipolar system using hydrogen peroxide (H₂O₂) and glucose as analytes. Ag/AgCl was also effective in adjusting the sensitivity to these analytes to achieve the best performance. This method of interfacial potential control is expected to contribute toward the development of reliable sensing devices and applications such as redox cycling, which require precise potential control.     

Implementation of a Chloride‐selective Electrode Into a Closed Bipolar Electrode System with Fluorimetric Readout

Applicability of a bipolar electrode system was tested for arrangements containing a typical ion‐selective electrode (ISE) connected with an electrode coated by a conducting polymer characterized by electroluminescence. In this case a selective response of the ISE membrane at one pole of the bipolar electrode is transduced to a fluorimetric signal obtained by reduction of the conducting polymer at the second pole. This signal transformation mode was studied on example of a simple closed bipolar electrode system composed of all‐solid‐state chloride‐selective electrode with polypyrrole transducer as the sensing pole and the reporting pole represented by electrode coated by poly(3‐octylthiophene) (POT) layer characterized by fluorescence in the neutral state. In this system selective and linear dependences of fluorimetric signal on logarithm of chloride ions concentration in turn‐on mode were recorded for optimized external voltage applied. Alternatively, a concept of cascade bipolar electrode system with incorporation of additional bipolar electrode being a polarization source for the sensing bipolar electrode with ISE and POT layer was also tested. A significant advantage of the cascade system is its possibility to work spontaneously without external polarization. For this case also linear calibration plots of fluorimetric signal vs. logarithm of analyte concentration were recorded.     

Two-channel microelectrochemical bipolar electrode sensor array

We report a two-channel microelectrochemical sensor that communicates between separate sensing and reporting microchannels via one or more bipolar electrodes (BPEs). Depending on the contents of each microchannel and the voltage applied across the BPE, faradaic reactions may be activated simultaneously in both channels. As presently configured, one end of the BPE is designated as the sensing pole and the other as the reporting pole. When the sensing pole is activated by a target, electrogenerated chemiluminescence (ECL) is emitted at the reporting pole. Compared to previously reported single-channel BPE sensors, the key advantage of the multichannel architecture reported here is physical separation of the ECL reporting cocktail and the solution containing the target. This prevents chemical interference between the two channels.     

Intracellular Wireless Analysis of Single Cells by Bipolar Electrochemiluminescence Confined in a Nanopipette

The inside walls of a nanopipette tip are decorated by a Pt deposit that is used as an open bipolar electrochemiluminescence (ECL) device to achieve intracellular wireless electroanalysis. The synergetic actions of nanopipette and of bipolar ECL lead to the spatial confinement of the voltage drop at the level of the Pt deposit, which generates ECL emission from luminol. The porous structure of Pt deposit permits the electrochemical transport of intracellular molecules into the nanopipette that is coupled with enzymatic reactions. Thus, the intracellular concentrations of hydrogen peroxide or glucose are measured in vivo as well as the intracellular sphingomyelinase activity. In comparison with the classic bipolar ECL, the remarkably low potential applied in our approach is restricted inside the nanopipette and it minimizes the potential bias of the voltage on the cellular activity. Accordingly, this wireless ECL approach provides a new direction for analysis of single living cells.     

Shaping and exploring the micro- and nanoworld using bipolar electrochemistry

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.     

Digital versatile disc bipolar electrode: A fast and low-cost approach for visual sensing of analytes and electrocatalysts screening

This work represents a new, extremely low cost and easy method for fabrication of bipolar electrode (BPE) for rapid and simultaneous screening of potential candidates for electrocatalytic reactions and sensing applications. Our method takes advantage of the silver reflective layer deposited on already available recordable digital versatile disc (DVD-R) polycarbonate substrate which acts as BPE. Oxidation of the reflective layer of the DVD-R in anodic pole of the BPE results in a permanent and visually measurable dissolute length. Therefore, one could correlate the electrocatalytic activity of the catalyst at the cathodic pole of the BPE, as well as the concentration of analyte in the solution, to the dissolution length of the BPE. To illustrate the promising applications of this new substrate as BPE, p-benzoquinone (BQ) and hydrogen peroxide were tested as model targets for the sensing application. Moreover, in order to show the feasibility of using DVD BPEs for screening applications, the electrocatalytic activity of Pt, Pd, Au, and pristine DVD substrate toward hydrogen evolution reaction (HER) were compared using an array of BPEs prepared on DVD substrate.     

Bipolar electrochemistry for cargo-lifting in fluid channels

We report for the first time the vertical propulsion of conducting beads in liquid filled capillaries by bipolar electrochemistry. The beads, when exposed to an external electric field, act as bipolar electrodes showing hydroquinone oxidation on one side and proton reduction on the other side. The related asymmetric bubble generation occurring at the bottom part of the beads drives their motion. The characteristic features of the propulsion can be tuned by changing parameters such as the applied electric field or the capillary shape. Using a conical capillary, we show that a Yo-Yo type motion can be induced. The quite versatile concept can then be used for cargo-lifting and is of potential interest for microfluidic applications in LOC devices.     

Label-Free Electrochemiluminescence Imaging of Single-Cell Adhesions by Using Bipolar Nanoelectrode Array

A label-free and fast approach for positive electrochemiluminescence (ECL) imaging of single cells by bipolar nanoelectrode array is proposed. The reduction of oxygen at a platinized gold nanoelectrode array in a closed bipolar electrochemical system is coupled with an oxidative ECL process at the anodic side. For elevating the ECL imaging contrast of single cells, a driving voltage of −2.0 V is applied to in situ generate oxygen confined beneath cells that is subsequently used for ECL imaging at 1.1 V. High oxygen concentration in the confined space resulting from steric hindrance generates prominent oxygen reduction current at the cathodic side and higher ECL intensity at the anodic side, allowing positive ECL imaging of the cells adhesion region with excellent contrast. Cell morphology and adhesion strength can be successfully imaged with high image acquisition rate. This approach opens a new avenue for label-free imaging of single cells.     

A method for the determination of speed-dependent semi-classical vector correlations from sliced image anisotropies

We present analytical expressions relating the bipolar moment β(Q)(K)(k(1)k(2)) parameters of Dixon to the measured anisotropy parameters of different pump/probe geometry sliced ion images. In the semi-classical limit, when there is no significant coherent contribution from multiple excited states to fragment angular momentum polarization, the anisotropy of the images alone is sufficient to extract the β(Q)(K)(k(1)k(2)) parameters with no need to reference relative image intensities. The analysis of sliced images is advantageous since the anisotropy can be directly obtained from the image at any radius without the need for 3D-deconvolution, which is not applicable for most pump/probe geometries. This method is therefore ideally suited for systems which result in a broad distribution of fragment velocities. The bipolar moment parameters are obtained for NO(2) dissociation at 355 nm using these equations, and are compared to the bipolar moment parameters obtained from a proven iterative fitting technique for crushed ion images. Additionally, the utility of these equations in extracting speed-dependent bipolar moments is demonstrated on the recently investigated NO(3) system.     

Buildup of ultrathin multilayer films by a self-assembly process, 1 consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces

An anionic and a cationic bipolar amphiphile containing rigid biphenyl cores were synthesized. The compounds were dissolved in a mixture of dimethylsulfoxide (DMSO) and water and pure water, respectively. When a solid substrate with a positively charged planar surface is immersed in the solution containing the negatively charged bipolar amphiphile, a monolayer of the amphiphile is adsorbed and due to its bipolar structure the surface charge is reversed. After rinsing in pure water the substrate is immersed in the solution containing the positively charged bipolar amphiphile. Again a monolayer is adsorbed but now the original surface charge is restored. By repeating both steps in a cyclic fashion alternating multilayer assemblies of both compounds are obtained. It is demonstrated that multilayer films, composed of at least 35 consecutively alternating layers, which corresponds to a total film thickness of 170 nm can be assembled.     

A Resettable Keypad Lock with Visible Readout Based on Closed Bipolar Electrochemistry and Electrochromic Poly(3‐methylthiophene) Films

A closed bipolar electrode (BPE) system was developed with electrochromic poly(3‐methylthiophene) (PMT) films electropolymerized on the ITO/rGO electrode as one pole of BPE in the reporting reservoir and the bare ITO electrode as another pole of BPE in the analyte reservoir, in which rGO represents reduced graphene oxide. Under a suitable driving voltage (V_tot), the electrochemical reduction/oxidation of electroactive probes, such as H₂O₂/glutathione (Glu), in the analyte reservoir could induce the reversible color change of PMT films in the reporting reservoir between blue and red. Based on this, a keypad lock with H₂O₂, Glu, and V_tot=?3.0 V as the three inputs and the color change of PMT films as the visible output was established. This system was easily operated and did not need to synthesize the complex compounds or DNA molecules. The security system was easy to reset and could be used repeatedly.     

Fundamental studies on the intermediate layer of a bipolar membrane: Part III. Effect of starburst dendrimer PAMAM on water dissociation at the interface of a bipolar membrane

Starburst dendrimer polyamidoamine (PAMAM) with ellipsoidal or spheroidal shape is structure-regular and has much more amino groups than conventional polymers. This paper investigates the possibility of these amino groups on water dissociation in a bipolar membrane interface. To do this, a bipolar membrane is prepared by casting the solution of sulfonated poly(phenylene oxide) (SPPO) in dimethyl formamide (DMF) on a commercial anion exchange membrane that is immersed in PAMAM aqueous solution in advance. The existence of PAMAM adsorbed on the membrane is proved by X-ray photoelectron spectroscopy (XPS), and the adsorption amount is evaluated by weighting method. The junction thickness of the prepared bipolar membrane is determined by electrochemical impedance spectroscopy (EIS), and the performance is evaluated by current–voltage curves. The experiments show that both the generation and concentration of PAMAM would strongly affect the characteristics of the bipolar membranes. There exists a transitional concentration for various generations PAMAMs to catalyze effectively the water dissociation, and above or below the transitional concentration the performance of bipolar membranes is decreasing. The higher the generation, the lower the concentration. Moreover, at a fixed solution concentration, there is not the simple relation of monotone decreasing or increasing between the performance of bipolar membranes and the generations of PAMAMs. All these can be explained according to the characteristics of PAMAMs combined with available water dissociation theory.     

铝型材电泳涂装小试工艺中影响漆膜质量的几个因素的研究

研究了实验室小试条件下电压、时间、极距等因素对铝型材阳极电泳涂膜厚度及膜层外观的影响,确定了电泳涂装的较佳工艺:电压130 V,时间130～230 s,极距88～110 mm,室温下进行.在此条件下的电泳涂膜厚度可达21 μm以上,合乎工艺的生产要求.且各项耐蚀性检测结果较好.     

Cell membrane electropermeabilization by symmetrical bipolar rectangular pulses. Part II. Reduced electrolytic contamination

The paper presents a comparative study of the contamination of a cell suspension by ions released from aluminum cuvettes (Al(3+)) and stainless steel electrodes (Fe(2+)/Fe(3+)) during cell membrane electropermeabilization by unipolar and by symmetrical bipolar rectangular electric pulses. A single pulse and a train of eight pulses were delivered to electrodes at a 2-mm distance, with 100-micros and 1-ms pulse durations, and amplitudes ranging from 0 to 400 V for unipolar, and from 0 to 280 V for bipolar pulses. We found that the released concentrations of Al(3+) and Fe(2+)/Fe(3+) were always more than one order of magnitude lower with bipolar pulses than with unipolar pulses of the same amplitude and duration. We then investigated the viability of DC-3F cells after 1 h of incubation in the medium containing different concentrations of Al(3+) or Fe(2+)/Fe(3+) within the range of measured released concentrations (up to 2.5 mM for both ions), thus separating the effects of electrolytic contamination from the effects of electropermeabilization itself. For Fe(2+)/Fe(3+), loss of cell viability became significant at concentrations above 1.5 mM, while for Al(3+), no effect on cell survival was detected within the investigated range. Still, reports on the biochemical effects of released Al(3+) also suggest that with aluminum cuvettes, electrolytic contamination can be detrimental. Our study shows that electrolytic contamination and its detrimental effects can be largely reduced with no loss in efficiency of electropermeabilization, if bipolar rectangular pulses of the same amplitude and duration are used instead of the commonly applied unipolar pulses.     

双极性半导体钝化膜空间电荷电容分析(II)

将双极性半导体钝化膜空间电荷电容等效为钝化膜/溶液界面处电容和内层钝化膜/外层钝化膜界面处的np结电容的串联, 根据前期研究建立的半导体富集态、耗尽态以及反型态空间电荷电容的统一计算公式, 给出了双极性钝化膜Mott-Schottky(M-S)曲线的非线性拟合方法. 并将这一方法应用于镍基合金G3高温高压H2S/CO2腐蚀后的钝化膜半导体特征研究. M-S曲线非线性拟合结果显示, 温度升高外层p型半导体钝化膜多数载流子浓度明显增高, 而内层n型半导体钝化膜的多数载流子浓度基本未变. 通过非线性拟合, 证明本文所给出的M-S曲线非线性拟合方法能够同时给出钝化膜内外层多个半导体性质参数,为揭示钝化膜形成及破坏机制提供更多信息. 结合X射线光电子能谱(XPS)分析, 讨论了钝化膜结构变化机制及np结在抑制腐蚀过程中的作用.     

Spatially-resolved multicolor bipolar electrochemiluminescence

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.     

Bipolar electrode depletion: membraneless filtration of charged species using an electrogenerated electric field gradient

We report a method for removing ions from aqueous solutions without the use of a membrane. The approach, which we call bipolar electrode depletion (BED), is based on the formation of an asymmetric electric field profile in a microchannel containing a bipolar electrode (BPE). The asymmetric field arises from local increases in conductivity caused by faradaic reactions at the BPE. We show how the asymmetric field can be used to deplete anions from a microchannel via a combination of electrophoresis and electroosmosis. We also apply this approach to filter an anionic species from a mixture of charged and neutral species being transported through a microchannel via electroosmosis. This technique could be utilized for desalination or filtration of any species possessing a net charge (e.g. heavy-metals, bacteria, proteins, or functionalized-nanoparticles).     

Bipolar Electrochemistry

A bipolar electrode (BPE) is an electrically conductive material that promotes electrochemical reactions at its extremities (poles) even in the absence of a direct ohmic contact. More specifically, when sufficient voltage is applied to an electrolyte solution in which a BPE is immersed, the potential difference between the BPE and the solution drives oxidation and reduction reactions. Because no direct electrical connection is required to activate redox reactions, large arrays of electrodes can be controlled with just a single DC power supply or even a battery. The wireless aspect of BPEs also makes it possible to electrosynthesize and screen novel materials for a wide variety of applications. Finally, bipolar electrochemistry enables mobile electrodes, dubbed microswimmers, that are able to move freely in solution.     

Influence of medium and temperature on the hydrolysis kinetics of propacetamol hydrochloride: determination using derivative spectrophotometry

Propacetamol hydrochloride (PRO) is a water-soluble prodrug of paracetamol (PA) which can be parenterally administered as analgesic for the treatment of postoperative pain, acute trauma, and gastric and/or intestinal disorders where oral administration is not possible. In these circumstances, PRO can be administered in physiologic or glucose solutions since it is rapidly and quantitatively hydrolyzed into PA by plasma estearases. We have studied the degradation kinetics of PRO in 5% glucose and 0.9% saline solutions at 4 degrees C and 25 degrees C (storage and room temperatures, respectively). The analytic technique used to determine PRO and PA quantitatively was first-derivative spectrophotometry. The degradation process of PRO can be best fitted to a second-order kinetics with independence of the medium used (saline or glucose solution). The hydrolysis kinetics of PRO conversion into PA depends on the temperature but not on the assay medium (saline or glucose solution). The degradation rate constants obtained for PRO were approximately 4.5 times higher at 25 degrees C than at 4 degrees C. The values of t(90%) for PRO were 3.17 h and 3.61 h at 25 degrees C, and 13.42 h and 12.36 h at 4 degrees C when the tests were performed in 5% glucose and 0.9% saline solutions, respectively.     

Alternating current-bipolar electrochemistry

Rotation of a bipolar electrode in a constant electric field between feeder electrodes causes an alternating bipolar current at an AC frequency that depends on the rotation rate. The corresponding oscillation of the feeder current is evaluated by means of a lock-in amplifier. This innovative approach allows the current flowing through the non-wired bipolar electrode in an open bipolar system to be extracted without relying on electrochemical reporter reactions.