Conventional Disc Electrodes Research Articles

A beveled working electrode coupled to a sandglass shape detection cell: A strategy to improve the sensitivity of electrochemiluminescence detection in microchip electrophoresis

A beveled working electrode (WE) with a sandglass shape electrochemiluminescence (ECL) detection cell based on tris(2,2′-bipyridyl)ruthenium(II) (TBR) for microchip capillary electrophoresis (MCE) was described in this paper. The beveled WE was readily fabricated from a platinum (Pt) wire (0.3mm diameter). The microchip comprised of three layers: top polydimethylsiloxane (PDMS) layer, middle glass plate, and bottom glass coverslip. The middle layer was a glass wafer on which the injection and separation channels were etched; meanwhile, an inverted funnel hole was made by a coniform drill, and a snot which was used to hold a guide tube aligning to the separation channel outlet was fabricated by a clubbed drill. The top layer was PDMS block containing four holes that connected injection channels and separation channel terminals, respectively. The two layers were bonded after their surfaces were processed by a plasma cleaner. The bottom layer was a coverslip (0.17mm thick) which covered the inverted funnel hole in the middle layer with epoxy resin. The beveled WE was inserted into the guide tube and immobilized using melt adhesive. A Pt wire acted as a counter electrode (CE) was penetrated through the PDMS layer perpendicularly to the WE, with a 1.5-mm long portion left inside the detection cell. Proline was used to evaluate the developed MCE–ECL microdevice with the limit of detection down to 0.2μM (S/N=3). The detection sensitivity was found to be improved remarkably, compared to the conventional disk electrode.

Lightweight, flexible, nanorod electrode with high electrocatalytic activity

We report on a dropcasting method to fabricate lightweight and mechanically flexible electrodes from gold nanorods. The nanorod electrodes possess extremely high electroactive areas, which lead to greatly enhanced electrocatalysis towards oxygen reduction reaction and methanol oxidation reaction when compared to conventional gold disk electrodes.

Active flexible concentric ring electrode for non-invasive surface bioelectrical recordings

Bioelectrical surface recordings are usually performed by unipolar or bipolar disc electrodes even though they entail the serious disadvantage of having poor spatial resolution. Concentric ring electrodes give improved spatial resolution, although this type of electrode has so far only been implemented in rigid substrates and as they are not adapted to the curvature of the recording surface may provide discomfort to the patient. Moreover, the signals recorded by these electrodes are usually lower in amplitude than conventional disc electrodes. The aim of this work was thus to develop and test a new modular active sensor made up of concentric ring electrodes printed on a flexible substrate by thick-film technology together with a reusable battery-powered signal-conditioning circuit. Simultaneous ECG recording with both flexible and rigid concentric ring electrodes was carried out on ten healthy volunteers at rest and in motion. The results show that flexible concentric ring electrodes not only present lower skin–electrode contact impedance and lower baseline wander than rigid electrodes but are also less sensitive to interference and motion artefacts. We believe these electrodes, which allow bioelectric signals to be acquired non-invasively with better spatial resolution than conventional disc electrodes, to be a step forward in the development of new monitoring systems based on Laplacian potential recordings.

Palladium Paste Nanocomposite Electrode as a New Metallic Electrocatalyst for Ethanol Oxidation and Nonenzymatic Amperometric Sensor in Alkaline Medium

AbstractPalladium paste nanocomposite electrode was employed as an efficient electrocatalyst for ethanol oxidation and nonenzymatic amperometric ethanol sensor, in alkaline media. The combined application of unique properties of nanomaterials and ionic liquids results in electrodes with interesting advantages compared to the conventional Pd disk electrodes. High tolerance towards accumulation of carbonaceous species (CO‐like intermediates) and poisoning by strongly adsorbed species suggests this electrode suitable for many applications. The sensor has the advantages of high sensitivity, low detection limit (20.0 µM), wide linear range (30.0 µM–1.6 M), ease of renewing the electrode surface, good long‐term stability and reproducibility for ethanol determination.

Metal Paste Nanocomposite Electrodes as a New Generation of Metallic Electrodes

Fabrication of metal paste nanocomposite electrodes is introduced using metal nanostructures and ionic liquids. The combined application of unique properties of nanomaterials and ionic liquids in the design of these metal paste nanocomposites results in electrodes with interesting advantages compared to the conventional metal disk electrodes. In contrast to conventional metallic electrodes, which are usually prone to fouling effects and suffer from weak repeatability and reproducibility, these metal paste nanocomposite electrodes have very exciting advantages. Ease of electrode fabrication; cleaning and activating the electrode surface, together with high electrocatalytic activity; increased degree of active area and surface roughness; antifouling effect; good signal-to-noise ratio; low cost; and low weight are among the advantageous features of these electrodes. Compared to dropping mercury electrodes that have high toxicity, these metal paste nanocomposite electrodes have much less toxicity. Such abilities promote new opportunities for a wide range of electrochemical, sensing, and biosensing applications.

Nanoelectrode ensembles for the direct voltammetric determination of trace iodide in water

Procedures for the preparation and characterisation of ensembles of gold nanodisk electrodes (NEE) of 30 nm diameter are presented, in particular focusing on improvements in the signal/background current ratios and detection limits with respect to the electrochemical oxidation of iodide and its analytical determination in water samples. At NEEs iodide undergoes a quasi-reversible diffusion controlled oxidation with a slight shift in E 1/2 values and slightly higher peak to peak separation with respect to conventional gold disk electrodes. The double layer charging current at the NEE is significantly lower than at conventional electrodes so that the detection limit (DL) by cyclic voltammetry with NEEs in tap water is significantly lower than DL at the Au-disk millimetre-sized electrode (DL 0.3 µM at NEE vs. 4 µM for Au-disk). Finally, it is shown that NEEs in combination with square wave voltammetry can be applied for the direct determination of iodide in water samples from the lagoon of Venice, with a detection limit of 0.10 µM.

Staple electrodes: an innovative alternative for intraoperative electrophysiological monitoring

Intraoperative electrophysiological monitoring is essential for minimally invasive neurosurgery. The authors developed an innovative recording method using a staple electrode, consisting of a surgical skin staple and an integrated circuit (IC) test clip with a cable. The staple is put on the patient's skin after the induction of general anesthesia. After head fixation, the IC test clip is simply hooked to the staple. The authors used this method for recording in 158 consecutive cases. It took only a few minutes to set up 4-18 staple electrodes in each case. None of the staple electrodes became disconnected unintentionally, and the initial impedance was kept throughout the procedures. The authors conclude that the staple electrode is superior to conventional disc or needle electrodes in speed of setup, electrical stability, and cost-effectiveness and recommend its routine use for intraoperative electrophysiological monitoring.

Improvement of spatial selectivity and decrease of mutual information of tri-polar concentric ring electrodes

Electroencephalography (EEG) signals are spatio-temporal in nature. EEG has very good temporal resolution but typically does not possess high spatial resolution. The surface Laplacian enhances the spatial resolution and selectivity of the surface electrical activity recording. Concentric ring electrodes have been shown to estimate the surface Laplacian directly with significantly better spatial resolution than conventional electrodes. For this report movement-related potentials (MRP) signals were analyzed. The signals were recorded using tri-polar ring electrodes in the original configuration as well as in bipolar and unipolar configurations achieved by excluding or shorting recording surfaces of the tri-polar version, respectively. The electrodes were placed in an array scheme of 35, encompassing the area between Fz-Cz-Pz-P3-T5-T3-F7-F3 centered on C3. Data were measured in five steps sequentially using only seven electrodes at a time, displaced after each step and aligned during evaluation later. Subjects were cued to press a micro-switch. The signal-to-noise ratio (SNR), spatial selectivity, and mutual information (MI) of the MRP signals recorded with the different electrode systems were compared. The MRP signals recorded with the tri-polar concentric ring electrode system have significantly higher SNR than from bipolar concentric ring electrode and conventional disc electrode emulations. The tri-polar electrodes have also shown significantly higher spatial selectivity as well as significantly less mutual information between locations than the other two electrode configurations tested. These characteristics should make tri-polar concentric electrodes beneficial for EEG applications.

Single-walled carbon nanotube-arrayed microelectrode chip for electrochemical analysis

The development of a single-walled carbon nanotube (SWCNT)-arrayed microelectrode chip is reported here. SWCNT-arrayed electrodes were formed directly on Pt surfaces, and were also arrayed on the chip. The electrochemical characteristics of the devices were investigated using potassium ferricyanide, K 3[Fe(CN) 6] in connection with cyclic voltammetry (CV). The electrochemical signals of electro-active amino acids; L-Tyrosine (Tyr), L-Cysteine (Cys) and L-Tryptophan (Trp) were detected using differential pulse voltammetry (DPV). The chip operated at a lower oxidation potential (vs. Ag/AgCl) compared with conventional carbon and Pt disc electrodes in 50 mM phosphate buffer solution (PBS, pH 7.4). The linear response was observed between 0.1–1 μM and 100 μM for the amino acids with correlation coefficients higher than 0.99. The electrochemical measurements of K 3[Fe(CN) 6] and amino acids revealed that the peak current intensities using SWCNT-arrayed electrodes were about 100-fold higher than those using bare Pt-arrayed microelectrodes. Additionally, the surface area dependence of the peak current responses was plotted. We concluded that our chips with SWCNT-arrayed microelectrodes provided a promising platform for electrochemical applications.

Pulsed Amperometric Detection of Histamine at Glassy Carbon Electrodes Modified with Gold Nanoparticles

AbstractGold nanocrystal‐modified glassy carbon electrodes (nAu‐GCE) were prepared and used for the determination of histamine by flow injection and high performance liquid chromatography using pulsed amperometric detection (PAD) as the detection mode. Experimental variables involved in the electrodeposition process of gold from a HAuCl4 solution were optimized. A catalytic enhancement of the histamine voltammetric response was observed at the nAu‐GCE when compared with that obtained at a conventional Au disk electrode, as a consequence of the microdispersion of gold nanocrystals on the GC substrate. The morphological and electrochemical characteristics of the nAu‐GCE were evaluated by SEM and cyclic voltammetry. PAD using a very simple potential waveform consisting of an anodic potential (+700 mV for 500 ms) and a cathodic potential (−300 mV for 30 ms), was used to avoid the electrode surface fouling when histamine was detected under flowing conditions. Flow injection amperometric responses showed much higher Ip values and signal‐to‐noise ratios at the nAu‐GCE than at a conventional gold disk electrode. A limit of detection of 6×10−7 mol L−1 histamine was obtained. HPLC‐PAD at the nAu‐GCE was used for the determination of histamine in the presence of other biogenic amines and indole. Histamine was determined in sardine samples spiked at a 50 μg g−1 concentration level, with good results. Furthermore, the chromatographic PAD method was also used for monitoring the formation of histamine during the decomposition process of sardine samples.

Influence of the biased electrode on the plasma potential in ECRIS

Dedicated experiments have been carried out at the Frankfurt 14 GHz electron cyclotron resonance ion source (ECRIS) by using a special double biased-electrode assembly, which consists of a conventional disk electrode and a separately biased ring electrode installed in front of it. In this assembly, the ring can be used to modulate the fluxes to the disk and allows a detailed study of the role of secondary electron fluxes in ECRIS operation. It was found that these fluxes contribute more than 50% to the total disk currents. However, blocking them did not result in a drop in the extracted ion currents. Instead, it was observed that, under certain operational conditions, the injection of secondary electrons results in a decrease in the extracted currents by up to 20%. Parallel to the double disk measurements, Langmuir probe measurements have been performed close to the position of Bmax. From the probe characteristics, plasma potentials were determined to be about +30 V at the conditions of the experiment. Applying a negative voltage to the double disk electrodes leads to a decrease of the plasma potential by approximately 5 V. Changes in the plasma shape were observed when the biased electrode voltage was changed. We conclude that the main effect of the biased electrode is a decrease of the plasma potential by reflecting a sufficient amount of electrons back to plasma, which otherwise would have been lost.

Studies on Glucose Biosensors Based on Nonmediated and Mediated Electrochemical Oxidation of Reduced Glucose Oxidase Encapsulated Within Organically Modified Sol-Gel Glasses

A new, organically modified sol-gel glass electrode is reported using 3-aminopropyltriethoxy silane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxy silane as sol-gel precursors for the construction of electrochemical biosensors. Four different systems of new sol-gel glass modified glucose electrodes are made in acidic medium having common sol-gel precursors and: 1) glucose oxidase, 2) glucose oxidase along with polyethylene glycol, 3) glucose oxidase and graphite powder, and 4) glucose oxidase along with polyethylene glycol and graphite powder. Both nonmediated and mediated electrochemical regeneration of immobilized glucose oxidase within sol-gel glasses are studied in these four systems. The nonmediated regeneration is achieved in the presence of oxygen as electron donor whereas mediated regeneration involves soluble ferrocene monocarboxylic acid as electron donor in each system. The electrochemical performance of sol-gel glass based biosensors is compared on the basis of cyclic voltammetry and amperometry. This leads to the observations: i) all four systems reach a diffusion limited condition associated with the transport of soluble ferrocene monocarboxylic acid as well as for dissolved oxygen within the sol-gel matrix, ii) the relative rate of diffusion of these analytes increases from system 1 to system 4, iii) both nonmediated and mediated amperometric responses at suitable potentials are based on the oxidation of H2O2 and enzymatically reduced soluble ferrocene with relatively amplified electrochemical signal of system 4. Data on the reduction of oxygen at conventional graphite disk electrode and at typical sol-gel glass modified electrode are reported.

Analytical Applications of Cylindrical Carbon Fiber Microelectrodes. Simultaneous Voltammetric Determination of Phenolic Antioxidants in Food

Cylindrical carbon fiber microelectrodes (CFMEs) (8 μm in diameter and 8 mm in length) have been used to determine the phenolic antioxidants tert-butylhydroxyanisole (BHA) and tert-butylhydroxytoluene (BHT) in acetonitrile medium. The electrochemical behavior of the CFMEs was tested using ferrocene in pure acetonitrile. Pretreatment of the microelectrodes was not necessary for the voltammetric analysis of the antioxidants BHA and BHT. The influence of the supporting electrolyte concentration on i p and E p values obtained by differential pulse voltammetry (DPV) has been evaluated. Detection limits close to 70 μg L -1 of BHA or BHT were achieved. Square-wave voltammetry (SWV) of these antioxidants at the CFMEs showed current densities remarkably higher than those obtained at a conventional glassy carbon disk electrode. A background current various orders of magnitude lower was also observed at the CFME. An optimization of square-wave parameters was performed in order to achieve the best sensitivity and resolution of the net current responses. Linear calibration graphs were obtained in the concentration ranges (1.0-10.0) x 10 -5 and (1.0-10.0) x 10 -6 mol L -l , their slopes being significantly higher than those obtained by DPV. Voltammograms from mixtures of BHA and BHT showed two well-defined oxidation peaks with a difference between peak potentials of ∼300 mV, which allows the simultaneous determination of both antioxidants in this medium. Interferences from other substances commonly present in commercial antioxidant mixtures were tested. The developed method by SWV was applied to determine BHA and BHT in spiked samples of dehydrated potato flakes.

Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at thick-film gold electrodes

Cyclic voltammetric and electrochemical impedance spectroscopic investigations of screen-printed, thick-film gold electrodes reveal significant differences when compared with conventional polished gold disk electrodes of comparable size. The rough and porous structure of the thick-film electrode surface leads to an actual electrode area which is increased six-fold compared to polished disk electrodes. Due to the catalytic properties of these surface structures it is possible to perform the electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) at relatively low overpotentials, i.e. +0.145 V vs. SCE. By operating electrodes at this potential, electrode fouling processes and interference from electroactive species, e.g. acetaminophen, are minimized. An amperometric glucose sensor based on polymer matrix-entrapped glucose dehydrogenase with a working potential of +0.145 V vs. SCE was successfully incorporated into a flow injection analysis (FIA) system.

The use of ultramicroelectrodes for the determination of diffusion coefficients

A combination of chronoamperometric and voltammetric responses at microdisk and conventional size disk electrodes respectively, was used to determine the diffusion coefficient of an electroactive species and the ultramicroelectrode diameter simultaneously. The method does not require knowledge of the bulk concentration and requires only the number of electrons participating in the electrode reaction and a value for the area of the conventional size disk electrode. Subsequent determination of the concentration of electroactive species is also possible. This approach is demonstrated by evaluating the diffusion coefficient of N,N,N′,N′-tetramethyl-p-phenylendiamine (TMPD) in pure and binary mixtures of aprotic solvents in perchlorate media. Parallel determinations were carried out from potentiodynamic I—E curves obtained for ultramicroelectrodes of different radii and corrected for ideal steady state conditions. The diffusion coefficients thus determined were in good agreement with those determined using other electrochemical techniques.

Preparation and characterization of a multi-cylinder microelectrode coupled with a conventional glassy carbon electrode and its application to the detection of dopamine

A multi-cylinder microelectrode coupled with a conventional glassy carbon disc electrode (MCM/GC) was prepared and characterized using cyclic voltammetry and chronoamperometry. It was demonstrated that in the same way as one observed a steady-state current at closely spaced microelectrodes when redox recycling takes place, the same effect can be obtained with the MCM/GC device. The experimental results obtained with K 3Fe(CN) 6 solutions were compared with a previously developed theory. Further, it was demonstrated that with a carbon fibre MCM/GC device, the voltammetric behaviour of dopamine is greatly improved by virtue of redox recycling, hence giving high sensitivity. The steady-state collection current was linearly related to dopamine concentration in the range 1 × 10 −4 to 5 × 10 −7 mol 1 −1, and the detection limit was 2 × 10 −7 mol 1 −1. The influence of coexisting ascorbic acid was also investigated. This device was applied successfully in the determination of dopamine hydrochloride in pharmaceutical preparations.

Reverse pulse voltammetry with waiting period at conventional disk electrodes: Theory

AbstractRegeneration of the initial concentrations at a solid, stationary disk electrode after each reverse pulse in the reverse pulse voltammetry simplifies interpretation of the experimental data but requires modification of the waveform. The modification examined in this work involved inserting a waiting period after each reverse pulse at the potential where the initial concentrations could be reproduced. For conventional disk sizes and a wide range of τ, which is the sum of generating time and pulse time, the minimum length of the waiting time was found theoretically to be 12τ.