Pt-black Electrodes Research Articles

Repeated and On-Demand Intracellular Recordings of Cardiomyocytes Derived from Human-Induced Pluripotent Stem Cells.

Pharmaceutical compounds may have cardiotoxic properties, triggering potentially life-threatening arrhythmias. To investigate proarrhythmic effects of drugs, the patch clamp technique has been used as the gold standard for characterizing the electrophysiology of cardiomyocytes in vitro. However, the applicability of this technology for drug screening is limited, as it is complex to use and features low throughput. Recent studies have demonstrated that 3D-nanostructured electrodes enable to obtain intracellular signals from many cardiomyocytes in parallel; however, the tedious electrode fabrication and limited measurement duration still remain major issues for cardiotoxicity testing. Here, we demonstrate how porous Pt-black electrodes, arranged in high-density micro-electrode arrays, can be used to record intracellular-like signals of cardiomyocytes at large scale repeatedly over an extended period of time. The developed technique, which yields highly parallelized electroporations using stimulation voltages around 1 V peak-to-peak amplitude, enabled intracellular-like recordings at high success rates without causing significant alteration in key electrophysiological features. In a proof-of-concept study, we investigated electrophysiological modulations induced by two clinically applied drugs, nifedipine and quinidine. As the obtained results were in good agreement with previously published data, we are confident that the developed technique has the potential to be routinely used in in vitro platforms for cardiotoxicity screening.

Electrolysis of ammonia in aqueous solution by platinum nanoparticles supported on carbon nanotube film electrode

Electrolysis of ammonia in an aqueous solution can generate hydrogen gas at room temperature. An anode reaction of nitrogen gas desorption on ammonia electrolysis has a much larger overvoltage than that of a cathode reaction, and one of the useful electrode catalysts for the anode reaction is platinum (Pt). In this study, in order to increase the surface area of Pt three-dimensionally, Pt nanoparticles are held on a sponge-like film of carbon nanotubes (CNTs) that has a large surface area of 5000–10000 cm2 per 1 cm2 of the CNT film. The electrodes were adapted to the ammonia electrolysis to increase the current density with a low overvoltage. The Pt nanoparticles were deposited on the CNTs by a polyol method at various temperatures, and the Pt nanoparticles supported on the CNT (Pt-CNT) electrodes were fabricated by vacuum filtration of the Pt-CNT dispersion. The size of the deposited Pt nanoparticles was approximately 2–3 nm. The maximum electrochemical surface area of the Pt nanoparticles was more than 250 cm2 per unit electrode area of 1 cm2. The Pt-CNT film electrode with a large surface area of the Pt catalyst increased the current density of the anode reaction compared with the Pt plate or the Pt-black electrodes. The Pt-CNT decreased both the activation overvoltage corresponding to the high Pt surface area and the concentration overvoltage corresponding to the three-dimensional structure of the CNT films. Moreover, it is clarified that the deactivation of the catalysts by the anode reaction does not occur below −0.2 V (vs Hg|HgO) for the Pt-CNT electrodes.

Durability of Long-Life Low Power Fuel Cells

Fuel cells have the potential to provide very low uninterrupted power for long periods (several decades) of time. The specifications for these applications can vary tremendously from transportation fuel cells that are a large driving force behind fuel cell development. For these applications, the fuel and oxidant supply are often required to be stored for the entire lifetime of the application; these systems have higher inherent safety and overall higher system energy density than batteries for these prolonged operational times. Many of the technical challenges are application dependent but can include: Fuel/oxidant loss (due to membrane/plates/seals permeability)Membrane degradation and thinning (due to high cell voltages)Passive system water managementOperation in uncontrolled environments (including operation a large temperature range and unpredictable/uncontrollable ambient atmospheres)Control of power transients (microwatt to watt power levels) The primary degradation modes expected for these applications involve the electrode layer, loss of catalytic activity, membrane thinning, changing hydrophobicity of carbon materials (which impacts water management) and corrosion of metallic bipolar plates (including increasing contact resistance). Electrode degradation involving performance loss of the cathode catalyst layer includes catalyst particle agglomeration, catalyst support corrosion, losses of catalyst layer porosity and loss of catalyst layer proton conductivity due to ionomer degradation. Depending on the systems load requirements, potential cycles can be many millions of cycles over decades long continuous operation. To minimize catalyst degradation, we expect that a Pt-black electrode will be superior compare to the Pt supported on carbon electrodes that are the preferred for transportation applications. To examine the durability of these catalysts we are conducting Accelerated Stress Testing (ASTs); Figure 1 shows an on-going test of a Pt-black catalyst over 1.3 million cycles. The square wave cycling induces Pt dissolution and re-precipitation (Ostwald ripening) of the platinum thus decreases the catalyst surface area. From Figure 1, catalyst surface area loss appears to have reached 30-35% loss, but has not substantially increased after about 750,000 cycles. To avoid large amounts of hydrogen loss due to membrane cross-over, we are exploring multiple layers of membrane to make a thick, mechanically reinforced and chemically stabilized membrane. A primary method to examine membrane degradation is to examine radical attack of the membrane at OCV conditions. Membrane thinning was measured at approximately 1.7 - 4.2 micron/year over a 2.4 year test with H2/air, at 25 C, which over a 20 year operational life extrapolates to34 - 83 micron. This suggests that a membrane of > 200 micron thick will be required for a 20 year operational life at low power levels. Figure 1

Downstream Simultaneous Electrochemical Detection of Primary Reactive Oxygen and Nitrogen Species Released by Cell Populations in an Integrated Microfluidic Device.

An innovative microfluidic platform was designed to monitor electrochemically four primary reactive oxygen (ROS) and reactive nitrogen species (RNS) released by aerobic cells. Taking advantage of the space confinement and electrode performances under flow conditions, only a few experiments were sufficient to directly provide significant statistical data relative to the average behavior of cells during oxidative-stress bursts. The microfluidic platform comprised an upstream microchamber for cell culture and four parallel microchannels located downstream for separately detecting H2O2, ONOO-, NO·, and NO2-. Amperometric measurements were performed at highly sensitive Pt-black electrodes implemented in the microchannels. RAW 264.7 macrophage secretions triggered by a calcium ionophore were used as a way to assess the performance, sensitivity, and specificity of the integrated microfluidic device. In comparison with some previous evaluations achieved from single-cell measurements, reproducible and relevant determinations validated the proof of concept of this microfluidic platform for analyzing statistically significant oxidative-stress responses of various cell types.

Corrosion Behaviors and Metal Ion Releases of Metallic Biomaterials in Simulated Body Fluid

[Introduction] One of the major problems associated with the use of metallic biomaterials is their corrosion. Corrosion reactions, which are unavoidable in metals, cause not only deterioration or fracture of the products but also serious harm to living tissue. Nevertheless, metallic biomaterials are commonly used in the fields of medicine and dentistry because of their superior mechanical properties: an excellent combination of strength and ductility, resulting in high fracture toughness can not be substituted by other materials. Therefore, highly corrosion-resistant metals and alloys such as Ti, Ti alloys, Co-Cr alloys, and stainless steels are used for implant devices. All of them show superior corrosion resistance results from the formation of a passive film on the surface of the metal. However, very small quantities of the metallic ions actually dissolve through the passive film on these metallic biomaterials. There are already many literatures about the corrosion resistance of metallic biomaterials about the breakdown of the passive film. However, very limited information is available concerning the corrosion rate and the change in the amount of the released metallic ions as a result of the slight corrosion reaction with stable passive film. Therefore, in this study, several corrosion tests and surface analyses were performed in a simulated body fluid to clear the difference in the corrosion behaviors of various metallic biomaterials. [Materials and Method] Disk shaped specimens of pure Ti, Ti-50.8mol%Ni superelastic alloy (Ti-Ni), Co-20Cr-15W-10Ni alloy (L605, Co-Cr), type 316L stainless steel (316 SS), and pure Zr were prepared. The specimens for corrosion tests were mechanically ground to #800 grit SiC abrasive paper. The specimens for XPS were additionally polished and mirror-finished with 9 μm diamond paste and 0.04 μm colloidal silica. The specimens were then ultrasonically cleaned in acetone and ethanol. In this study, the simulated body fluid, 5.85 gL-1 NaCl and 10.0 gL-1lactic acid, as a corrosion test solution was prepared. The pH of the solution was checked in advance and was confirmed to be within the range of 2.30 ± 0.05 just after preparation. This solution was intended to be an accelerated body fluid for rapid testing of corrosion measurements of dental metallic materials prescribed by ISO 10271. An anodic polarization measurement was performed with a potentiostat and a function generator. A saturated calomel electrode (SCE) and a Pt-black electrode were used as a reference and a counter electrode, respectively. The surface area of the working electrode contacting the electrolyte was 0.38 cm2. After immersing the specimens into the test solution at 37°C, the open circuit potential (OCP) was measured for 10 min. Thereafter, the gradient anodic potential was applied at a constant sweep rate of 1 mVs-1from OCP. EIS measurement was performed with an electrochemical measurement system. A couple of the specimen disks were prepared and embedded in cold mounting epoxy resin. After grinding the surface, the electrodes were immediately immersed in the test solution and placed face-to-face at a constant distance. EIS measurement was started with an alternative potential of 10 mV in amplitude just 10 min after immersion. The measurement was continued for 48 h. The dissolution test was performed to evaluate the corrosion rate and amounts of the released metal ions during the immersion in the test solution. Twenty mL of the test solution was then put into the glass bottle, followed by the specimen. The bottle was completely sealed and kept for 7 d. The concentrations of the metal ions were measured with ICP-AES. [Results and Discussion] The polarization curves of all specimens except 316L SS showed clear passive region. Ti-Ni and Co-Cr showed transpassive region from 1.3 and 0.8 VSCE, respectively. Zr occurred pitting corrosion at 0.5 VSCE. On the other hand, 316L SS did not passivate and actively dissolved in the test solution. The amounts of the released ions from 316L were much higher than those of another specimens. However, Ti-Ni released certain amount of Ni ions, which are very hazardous for metal allergy. On the other hand, the amounts of the ions from Co-Cr and Zr were almost same level as detection limit of ICP-AES. It indicates that the protective performances against mass transfer of Co-Cr and Zr are superior to those of other biomaterials. Curve fittings could be performed using a conventional equivalent circuit models. The corrosion rates of all specimens decreased during the immersion period. However, the declines in the corrosion rates of Co-Cr and Zr were much larger than those of Ti, Ti-Ni, and 316 SS. It agrees with the results from the dissolution test.

Electrochemical Detection of Nitric Oxide and Peroxynitrite Anion in Microchannels at Highly Sensitive Platinum-Black Coated Electrodes. Application to ROS and RNS Mixtures prior to Biological Investigations

The electrochemical detection of nitric oxide (NO) and peroxynitrite anion (ONOO−) was investigated at Pt-black electrodes in microchannels. Owing to the high reactivity of these species under conditions close to physiological media, kinetic parameters were determined before evaluating the detection performances from synthetic solutions. Highly sensitive and stable Pt-black electrodes allowed detection limits down to 30nM (NO) and 40nM (ONOO−) to be reached with very high sensitivities. As NO and ONOO− are two relevant biological molecules involved in oxidative stress their simultaneous detections with other major molecules like hydrogen peroxide and nitrite were also performed and validated experimentally at pH 8.4. These results demonstrated that relative ROS/RNS contents in synthetic mixtures can be easily assessed at selected detection potentials. Beyond the interest of using small volumes in microfluidic channels, optimization of detection requires precise conditions easy to implement. These were delineated to lead in microdevices to high-performances detection of oxidative stress metabolites either from analytes or from the production of a few living cells like macrophages.

Structure of the Voltammograms of the Platinum-Black Electrodes: Derivative Voltammetry and Data Fitting Analysis

Voltammograms of Pt-black electrodes were recorded in aerated 1M HClO4 solution, at T=298K, for three different upper values of the oxidation potential, Emax=1.6V, 1.44V and 1.39V. Numerical differentiation of the raw data enhanced details which hardly were visible in the original voltammograms. The derivative of the anodic current resided in well defined peaks attributed to two peaks-like electrode reactions (potential range 0.6V–1.0V) and a smooth reaction generating the anodic current plateau, at potential higher than 1V. The derivative of the cathodic peaks revealed that the cathodic current results from two reactions occurring simultaneously, but with different rates: the reduction of the adsorbed - OH* followed by that of the adsorbed–O*. The data fitting analysis was performed with the empirical kinetic equations based upon the sigmoid-like functions. The analysis confirmed the results found on the derivative voltammograms and enabled to compute the individual component of the anodic and cathodic branches. Complementary mass measurements with the electrochemical quartz crystal microbalance (EQCM) confirmed that both the oxidation and the reduction processes on the Pt-black electrodes consist of a complex succession of overlapping reactions associated with both the adsorbed - OH* and - O* species.

The resting-state of the Pt-black electrode in acid solution and the structure of the adsorption layer. Coulometric and electrochemical quartz crystal microbalance measurements

The properties of Pt-electrodes in 1 M HClO 4 solution, in air, were studied both in the resting-state and mild oxidation conditions, within the potential range of 1000 mV and 1600 mV. Cyclic voltammetry (CV) and cathodic stripping voltammetry (CSV) were used for coulometric determination of the amount of O-containing species adsorbed on the electrode surface during the oxidation–reduction reactions. Simultaneously, the mass of the adsorption layer was measured in situ, with the electrochemical quartz crystal microbalance (EQCM). The surface of the Pt-black electrode in the resting-state is covered with OH*-species (apparently a ML), which are spontaneously generated by immersion in the aqueous solution without any polarization potential. The surface of the Pt smooth electrode is covered uppermost by a sub-monolayer of oxygen, in similar conditions. The resting-state of the Pt-black electrode is characterized by a reproducible value of the rest potential, E r = 1040 ± 5 mV (average of 10 samples) and a reduction peak in CV mode at E ′ p = 791 ± 7 mV (average of 10 samples). In anodic polarization conditions, PtOH* is oxidized to PtO*, in CV mode, and to Pt(O 2)*, in the potentiostatic mode. The reduction peak of PtO* in CV mode is E ″ p = 694 ± 9 mV (average of 10 samples), indicating a stronger bond to the surface of the electrode. The yielding of Pt(O 2)* is not fast enough to accommodate the increase of the oxidation potential by finite sweep rate of the CV mode at 10 mV s −1. Therefore this oxidation level could not be achieved in CV mode. The prolonged oxidation in the potentiostatic mode results in the coverage of the surface of Pt-black electrode with a monolayer of (O 2)*-species.

Proton Conduction on Ionomer-Free Pt Surfaces

AC impedance was measured for PTFE-bound, unbound, and ionomer-bound Pt-black electrodes, as well as for a conventional Pt/Vulcan electrode. Adsorbed water contributes to the proton conduction on ionomer-free Pt black surfaces, which display a strong dependence on relative humidity. The conductivity was 1-2 orders of magnitude lower than that of ionomer-containing electrodes. While non-dimensional scaling of the impedance data indicates a single conduction mechanism occurring in each electrode type, activation energies suggest that the mechanisms were different between ionomer-free and ionomer-bound electrodes. Ionomer-bound electrodes show an activation energy that strongly depends upon RH, while that of ionomer-free Pt black does not. Remarkably, conductivity on Pt black is 2-3 orders of magnitude greater than that of bulk water, suggesting an enhanced conduction mechanism occurring at the Pt surface.

Highly sensitive and reusable Pt-black microfluidic electrodes for long-term electrochemical sensing

Highly sensitive, long-term stable and reusable microfluidics electrodes have been fabricated and evaluated using H 2O 2 and hydroquinone as model analytes. These electrodes composed of a 300 nm Pt-black layer situated on a 5 μm thick electrodeposited Au layer, provide effective protection against electrooxidation of an underlying chromium adhesion layer. Using repeated cyclic voltammetric (CV) sweeps in flowing buffer solution, highly sensitive Pt-black working electrodes were realized with five- (four-) decade linear dynamic range for H 2O 2 (hydroquinone) and low detection limit of 10 nM for H 2O 2 and 100 nM for hydroquinone. Moreover, high sensitivity for H 2O 2 was demonstrated at low (0.3 V vs. Ag/AgCl) oxidation potentials, together with long-term stability and reusability for at least 30 days. Microfluidic flow was employed for desorption and reactivation of the nominally planar Pt-black electrodes. Such electrocatalytic surface architecture should be appropriate for long-term electrochemical detection of various molecules and biomolecules as well as in reusable immunoassay configurations.

An unusually high sensitivity of Pt-black pH electrode

The potentials of Pt-black electrode using a copper conducting wire instead of the salt bridge in acid and alkaline solutions without the use of H2 evolution reactions were measured. There were three nonlinear portions in the calibration curve. Unusually, the potential slopes at pH 3–5 and 8–10 indicated 200 mV and 70 mV per pH, respectively. Such high sensitivity for pH slope, more than 4 times of usual 59 mV per pH, may be credited to the special properties of the Pt-black surface. SEM (scanning electronical microscopy) was applied to characterize the surface of the Pt-black electrode. Its working mechanism is well explained in the theory of capacitance potentials rather than Nernst’s redox potentials.

Sputter-Deposited Pt PEM Fuel Cell Electrodes: Particles vs Layers

Platinum catalyst layers with Pt loadings were deposited by magnetron sputtering from a variable deposition angle α onto gas diffusion layer (GDL) substrates and tested as cathode electrodes in proton exchange membrane (PEM) fuel cells using Nafion 1135 membranes and Teflon-bonded Pt-black electrode (TBPBE) anodes. Layers deposited at normal incidence are continuous and approximately replicate the rough surface morphology of the underlying GDL. In contrast, glancing angle deposition (GLAD) with and continuous substrate rotation yields highly porous layers consisting of vertically oriented Pt particles, high and wide, that are separated by . The particle electrodes exhibit a higher (lower) mass-specific performance than the continuous-layer electrodes for a high (low) current density . This is attributed to a higher porosity but lower overall electrochemically active surface area for the particles compared to the continuous layer. Increasing in particle cells from yields increasing potentials, but causes a voltage drop at , associated with the reduced pore density at large . Comparison cells with a TBPBE cathode exhibit comparatively low Tafel slopes but a lower Pt mass specific performance than the sputtered catalysts. Quantitative analyses of kinetic and mass-transport losses in the polarization curves suggest a competing microstructural effect, favoring mass-transport performance and an efficient oxygen reduction reaction for particle and continuous layer electrodes, respectively. The overall results suggest that in addition to the well-known promise of sputter-deposited Pt catalysts as an approach to increase Pt utilization at low loading, GLAD provides the unique ability to control Pt porosity and to achieve efficient reactant flow for high-current-density operation.

Avidin-Biotin System-Based Enzyme Multilayer Membranes for Biosensor Applications: Optimization of Loading of Choline Esterase and Choline Oxidase in the Bienzyme Membrane for Acetylcholine Biosensors

The loading of choline esterase (ChE) and choline oxidase (ChOx) in the enzyme membrane of an acetylcholine biosensor was optimized based on a layer-by-layer construction of the bienzyme layers on the surface of a platinum (Pt) and a Pt-black electrode. To this goal, ChE and ChOx were tagged with biotin residues, so that the enzymes could be built into the multilayer assemblies composed of monomolecular layers of the enzymes and avidin. The ChE/ChOx bienzyme multilayer-modified electrodes showed amperometric response to acetylcholine in solution, showing that ChE and ChOx catalyzed hydrolysis reaction of acetylcholine and an oxidation reaction of resulting choline, respectively, successively in the bienzyme layer. It was found that the acetylcholine sensor which is modified with 10-layer ChOx exhibited its maximum response to acetylcholine when additional 2 layers of ChE were added to the surface of the ChOx layer. This optimum ratio of ChE to ChOx in the bienzyme layer was reasonably explained in terms of the relative values of catalytic activity of the enzymes. The usefulness of the layer-by-layer deposition technique in optimizing the enzyme loading in bienzyme system is discussed in detail.

DEMS-cyclic voltammetry investigation of the electrochemistry of nitrogen compounds in 0.5 M potassium hydroxide

The electro-oxidation and -reduction of 0.05 M ammonia, 0.01 M hydroxylamine, 0.01 M sodium nitrite and 0.05 M sodium nitrate in 0.5 M KOH at Pt-black electrodes has been investigated using a combination of cyclic voltammetry with on-line MS analysis of volatile products (DEMS). All compounds investigated in this study form adsorbates with very similar properties. These adsorbates can be reduced to ammonia and oxidised to nitrogen. Ammonia is adsorbed anodically, while nitrite and nitrate are adsorbed cathodically. In contrast to the adsorbates of the other compounds, adsorbed nitrite can also be reduced to nitrogen oxides in addition to ammonia. The combination of cyclic voltammetry and on-line MS proves that the adsorbates do not consist solely of triple bonded nitrogen. Ammonia and hydroxylamine also form nitrogen oxides in bulk oxidation processes. For the first time, a reaction mechanism which takes into account the interconversion of nitrogen compounds and adsorbate processes is discussed.

Use of oxide electrodes for proton-conductor gas sensor

An amperometric proton-conductor CO sensor operative at room temperature was developed by using a couple of Pt-loaded oxide (SnO 2 and WO 3) electrodes. The CO sensitivity of this sensor was about 7 times higher than the H 2 sensitivity and the 90% response time about 3 min. On the other hand, the sensor became H 2-selective when a Pt-black electrode was combined with a Pt-loaded WO 3 electrode. The sensing mechanisms of the CO- and H 2-selective proton-conductor sensors are proposed.

CO and H2 Sensing Properties of Proton-Conductor Sensor Using Pt-Loaded Oxide Electrodes

Abstract An amperometric proton-conductor sensor was newly developed for the selective detection of CO at room temperature by using a couple of Pt-loaded oxide (SnO2 and WO3) electrodes. The CO sensitivity of the sensor element was about 7 times higher than the H2 sensitivity and the 90% response time was about 3 min. The selective detection of H2 was possible when a Pt-black electrode was combined with a Pt-loaded WO3 electrode.

Controlled-potential controlled-current electrolysis: In vitro and in vivo electrolysis of urea

A controlled-potential, controlled-current (c.p.c.c.) method for electrolysis has been developed. Electrolysis is performed under controlled oxidative and controlled reductive currents within preset upper and lower bound potentials. The c.p.c.c. approach accomplishes both electrolysis and electrode regeneration concurrently. Compared with the existing galvanostatic and/or controlled potential electrolysis, the present approach demonstrates a greater selectivity for the electroactive species. The approach has been applied to direct electrolysis of urea in physiologic solutions and in recirculated canine hemodialysate. No undesirable, harmful, or toxic products have been found. The Pt-black electrodes, rejuvenated during the electrolysis, were found to perform as well in a standard test as they had prior to electrolysis of the hemodialysate. In view of its selective and regenerative nature, c.p.c.c. electrolysis is thought to be suitable for urea removal in a closed-loop, regenerative hemodialysis system. It is also most likely adapatable to other electrolyses of clinical substances.

De-ureation by electrochemical oxidation

A study of the anodic oxidation of urea on a Pt-black electrode in K rebs-R inger bicarbonate buffer in the presence of glucose was performed. Changes in urea and glucose concentration, pH and anode half-cell potential were measured. At a current density of 0.5 mA cm −2 and an electrode area of 50 cm 2, 4×10 −4 mole urea was oxidized in a 15 h run. NH 4 +, NO − 3, and NO − 2 were not found as products of the oxidation. Calculations of coulombic utilization during the oxidation process were compatible with a 6-electron process. N 2, CO 2, and H 2O were the most likely products. The feasibility of developing an electrochemical de-ureator, utilizing electrocatalysts, electricity and air or O 2 for urea removal by a portable artificial kidney was explored.