Platinum Pseudo-reference Electrode Research Articles

An Electrochemical Amperometric Ethylene Sensor with Solid Polymer Electrolyte Based on Ionic Liquid.

An electrochemical amperometric ethylene sensor with solid polymer electrolyte (SPE) and semi-planar three electrode topology involving a working, pseudoreference, and counter electrode is presented. The polymer electrolyte is based on the ionic liquid 1-butyl 3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][NTf2] immobilized in a poly(vinylidene fluoride) matrix. An innovative aerosol-jet printing technique was used to deposit the gold working electrode (WE) on the solid polymer electrolyte layer to make a unique electrochemical active SPE/WE interface. The analyte, gaseous ethylene, was detected by oxidation at 800 mV vs. the platinum pseudoreference electrode. The sensor parameters such as sensitivity, response/recovery time, repeatability, hysteresis, and limits of detection and quantification were determined and their relation to the morphology and microstructure of the SPE/WE interface examined. The use of additive printing techniques for sensor preparation demonstrates the potential of polymer electrolytes with respect to the mass production of printed electrochemical gas sensors.

A lithium iron phosphate reference electrode for ionic liquid electrolytes

We report on the development of a very simple and robust reference electrode suitable for use in room temperature ionic liquids, that can be employed with planar devices. The reference electrode is based on LiFePO4 (LFP), a common cathode material in Li-ion batteries, which is air and water stable. The reference electrode can be drop-cast onto a planar electrode device in a single step. We demonstrate that very low Li+-ion concentrations (millimolar or below) are sufficient to obtain a stable and reproducible LFP potential, thus making physical separation between the reference and working electrode unnecessary. Most importantly, the LFP potential is also entirely stable in the presence of oxygen and shows only a very small drift (<10 mV) in the presence of hydrogen gas, while the potential of a platinum pseudo-reference electrode is shifted >800 mV. This is the first time that such a stable reference electrode system for ionic liquids has been implemented in miniaturized, planar electrode devices.

Classification of Fertilizer Solutions by Micro-Volume Voltammetric Electronic Tongue with Two Sensing Electrodes

A micro-volume electronic tongue based on cyclic voltammetry with two sensing electrodes (gold and carbon) and a platinum pseudo-reference electrode is proposed to classify fertilizers and monitor fertilizer uptakes. The electronic tongue has been employed to classify three different types of commercial fertilizers and their mixture. The nutrient uptake of Dracaena Sanderiana (D. Sanderiana) planted in crystal soil with the mixture fertilizer was monitored by sampling the fertilizer solutions with the electronic tongue over a period of one week. The contents of macronutrients in the solutions were also analyzed by the standard spectroscopic techniques for comparison. A good agreement is obtained between the relative uptakes of phosphate and potassium from the electronic tongue analysis and those from the standard analytical techniques.

A reference electrode for use in supercritical difluoromethane

We describe the assembly and characterisation of a reference electrode for use in supercritical difluoromethane (R32). The reference electrode is constructed from a europium doped lanthanum fluoride crystal contacted by silver loaded epoxy and encased in a silicate epoxy. The reference electrode can withstand pressures and temperatures up to at least 20MPa and 360K, typical operating condition for electrochemistry in supercritical difluoromethane (scR32). The performance of the new reference electrode is compared to that of a platinum pseudo reference electrode in scR32. The redox potential of the decamethylferrocene couple in scR32 containing 20mM [NBun4][BF4] at ∼17.6MPa and 359K was 0.088±0.015V against the new silver contacted lanthanum fluoride crystal based reference electrode.

Ionic Liquid based polymer electrolytes for electrochemical sensors

Amperometric NO2 printed sensor with a new type of solid polymer electrolyte and a carbon working electrode has been developed. The electrolytes based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][N(Tf)2], 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][CF3SO3] and 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4] ionic liquids were immobilized in poly(vinylidene fluoride) matrix [PVDF]. The analyte, gaseous nitrogen dioxide, was detected by reduction at -500 mV vs. platinum pseudoreference electrode. The sensors showed a linear behavior in the whole tested range, i.e., 0 - 5 ppm and their sensitivities were in order of 0.3 x∙10-6 A/ppm. The sensor sensitivity was influenced by the electric conductivity of printing formulation; the higher the conductivity, the higher the sensor sensitivity. The rise/recovery times were in order of tens of seconds. The use of screen printing technology and platinum pseudoreference electrode simplify the sensor fabrication and it does not have any negative effect on the sensor stability.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7371

Effect of the geometry of a working electrode on the behavior of a planar amperometric NO2 sensor based on solid polymer electrolyte

An amperometric NO2 sensor with a new type of solid polymer electrolyte (SPE) and a glassy carbon working electrode is presented. The electrolyte is based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim][NTf2] ionic liquid immobilized in poly(vinylidene fluoride) matrix [PVDF]. The analyte, gaseous nitrogen dioxide, was detected by reduction at −500mV vs. a platinum pseudoreference electrode. The sensor exhibited a linear behavior in the whole tested range, i.e., 0–10ppm, and its sensitivity was 0.66×10−6A/ppm. The rise/recovery times were of the order of tens of seconds. In addition, the influence of the geometry (area and thickness) of the carbon working electrode on sensor response during short-term and long-term exposure to nitrogen dioxide was investigated. The area of the working electrode strongly influenced the stability and noise of the sensor: the smaller the electrode area, the better the stability of the sensor and the lower the noise level. The response times were influenced by the thickness of the carbon working electrode: the thicker the electrode, the longer the response time. It was also demonstrated that glassy carbon is a good candidate for the preparation of the working electrode. The use of a platinum pseudoreference electrode simplifies sensor fabrication and does not have any negative effect on sensor stability.

Gold nanowire electrodes in array: simulation study and experiments

Recent developments in nanofabrication have enabled fabrication of robust and reproducible nanoelectrodes with enhanced performance, when compared to microelectrodes. A hybrid electron beam/photolithography technique is shown that permits discrete gold nanowire electrode arrays to be routinely fabricated at reasonable cost. Fabricated devices include twelve gold nanowire working electrode arrays, an on-chip gold counter electrode and an on-chip platinum pseudo reference electrode. Using potential sweep techniques, when diffusionally independent, these nanowires exhibit measurable currents in the nanoAmpere regime and display steady-state voltammograms even at very high scan rates (5000 mV s(-1)) indicative of fast analyte mass transport to the electrode. Nanowire electrode arrays offer the potential for enhancements in electroanalysis including increased signal to noise ratio and increased sensitivity while also allowing quantitative detection at much lower concentrations. However, to achieve this goal a full understanding of the diffusion profiles existing at nanowire arrays is required. To this end, we simulate the effects of altering inter-electrode separations on analyte diffusion for a range of scan rates at nanowire electrode arrays, and perform the corresponding experiments. We show that arrays with diffusionally independent concentration profiles demonstrate superior electrochemical performance compared to arrays with overlapping diffusion profiles when employing sweep voltammetric techniques. By contrast, we show that arrays with diffusionally overlapping profiles exhibit enhanced performance when employing step voltammetric techniques.

Characterization of Novel Microelectrode Geometries for Detection of Neurotransmitters

In this paper, a microelectrode array is introduced and characterized using differential pulse voltammetry (DPV), amperometry and fast scan cyclic voltammetry with norepinephrine as a model neurotransmitter. Twenty-one sensor geometries were evaluated with DPV to determine optimal electrode configurations. Next, electrode responses were characterized for the best electrode geometry using an onboard platinum pseudo-reference electrode, whose reliability is established.

A study of iodine adlayers on polycrystalline gold electrodes by in situ electrochemical Rutherford backscattering (ECRBS)

Iodine adsorption on a polycrystalline gold electrode was studied by in situ electrochemical Rutherford backscattering (ECRBS) using an ultrahigh vacuum (UHV)-electrochemical cell comprising of a thin-film silicon nitride window. The depth resolution of RBS allowed for measurement of nuclide concentration of the diffuse double-layer, electrode surface and near-surface regions. ECRBS measurements on the gold electrode, initially exposed to −500 mV vs. a platinum pseudo-reference electrode, in a potassium iodide solution, showed an increase in the 2.07 MeV iodine peak indicative of iodine adsorption. The surface concentration of the iodine adlayer was directly measured by ECRBS to be 1.3 ± 0.3 nmol/cm 2. ECRBS measurements on a gold electrode exposed to 1.5 V vs. a platinum pseudo-reference electrode, in a potassium iodide solution display a decrease in the 2.16 MeV gold peak and a shift to lower energies. Scanning electron microscopy images of electrodes studied by ECRBS displayed roughened surfaces consistent with gold dissolution. This work demonstrates the potential for in situ ECRBS using thin-film silicon nitride windows to become a powerful tool for the investigation of a wide range of electrochemical processes in areas such as corrosion, electrodeposition and electrocatalysis.

New technology for multi-sensor silicon needles for biomedical applications

A multi-sensor silicon needle including two ion-sensitive field effect transistor (ISFET) sensors, a platinum pseudo-reference electrode (Pt) and a temperature sensor has been fabricated by using a CMOS-compatible technology and silicon micromachining. This paper presents a summary of the fabrication process and results of the device characterisation. The feasibility of the fabrication technology has been demonstrated and all devices have operated satisfactorily, with a response showing good sensitivity and linearity. The multi-sensor has been developed for the detection of myocardial ischemia during cardiac surgery.

Electrogenerated chemiluminescence of luminol for oxidase-based fibre-optic biosensors.

The luminol electrochemiluminescence has been exploited for the development of several fibre-optic biosensors allowing the detection of hydrogen peroxide and of substrates of H(2)O(2)-producing oxidases. Electro-optical flow injection analysis of glucose, lactate, cholesterol and choline are thus described. To perform the experiments, a glassy carbon electrode was polarized at a fixed potential. Luminol was then electrochemically oxidized and could react in the presence of hydrogen peroxide to produce light. Several parameters had to be optimized to obtain reliable optical biosensors. An optimum applied potential of +425 mV between the glassy carbon electrode and the platinum pseudo-reference electrode was determined, allowing the best signal: noise ratio to be obtained. It was also necessary to optimize the experimental conditions for the immobilization of the different oxidases involved (preactivated membranes, chemically activated collagen membranes, photopolymerized matrix). For each biosensor developed, the optimum reaction conditions have been studied: buffer composition, pH, temperature, flow rate and luminol concentration. Under optimal conditions, the detection limits (S/N = 3) were 30 pmol, 60 pmol, 0.6 nmol and 10 pmol for lactate, glucose, cholesterol and choline, respectively. The miniaturization of electrochemiluminescence-based biosensors has been realized using screen-printed electrodes instead of a glassy carbon macroelectrode, with choline oxidase as a model H(2)O(2)-generating oxidase.

Electrogenerated chemiluminescence of luminol for oxidase‐based fibre‐optic biosensors

The luminol electrochemiluminescence has been exploited for the development of several fibre-optic biosensors allowing the detection of hydrogen peroxide and of substrates of H2O2-producing oxidases. Electro-optical flow injection analysis of glucose, lactate, cholesterol and choline are thus described. To perform the experiments, a glassy carbon electrode was polarized at a fixed potential. Luminol was then electrochemically oxidized and could react in the presence of hydrogen peroxide to produce light. Several parameters had to be optimized to obtain reliable optical biosensors. An optimum applied potential of +425 mV between the glassy carbon electrode and the platinum pseudo-reference electrode was determined, allowing the best signal: noise ratio to be obtained. It was also necessary to optimize the experimental conditions for the immobilization of the different oxidases involved (preactivated membranes, chemically activated collagen membranes, photopolymerized matrix). For each biosensor developed, the optimum reaction conditions have been studied: buffer composition, pH, temperature, flow rate and luminol concentration. Under optimal conditions, the detection limits (S/N = 3) were 30 pmol, 60 pmol, 0.6 nmol and 10 pmol for lactate, glucose, cholesterol and choline, respectively. The miniaturization of electrochemiluminescence-based biosensors has been realized using screen-printed electrodes instead of a glassy carbon macroelectrode, with choline oxidase as a model H2O2-generating oxidase. Copyright © 2001 John Wiley & Sons, Ltd.

An electrochemiluminescence-based fibre optic biosensor for choline flow injection analysis.

A fibre optic biosensor based on luminol electrochemiluminescence (ECL) integrated in a flow injection analysis (FIA) system was developed for the detection of choline. The electrochemiluminescence of luminol was generated by a glassy carbon electrode polarised at +425 mV vs. a platinum pseudo-reference electrode. Choline oxidase (Chx) was immobilised either covalently on polyamide (ABC type) or on UltraBind preactivated membranes, or by physical entrapment in a photo-cross-linkable poly(vinyl alcohol) polymer (PVA-SbQ) alone or after absorption on a weak anion exchanger, DEAE (diethylaminoethyl) Sepharose. The optimisation of the reaction conditions and physicochemical parameters influencing the FIA biosensor response demonstrated that the choline biosensor exhibited the best performances in a 30 mM veronal buffer containing 30 mM KCl and 1.5 mM MgCl2, at pH 9. The use of a 0.5 ml min-1 flow rate enabled the measurement of choline by the membrane-based ECL biosensors in 8 or 5 min, with ABC or UltraBind membranes, respectively, whereas the measurement required only 3 min with the DEAE-PVA system. For comparison, the detection of choline was performed with Chx immobilised using the four different supports. The best performances were obtained with the DEAE-PVA-Chx sensing layer, which allowed a detection limit of 10 pmol, whereas with the ABC, the UltraBind and the PVA systems, the detection limits were 300 pmol, 75 pmol and 220 pmol, respectively. The DEAE-based system also exhibited a good operational stability since 160 repeated measurements of 3 nmol of choline could be performed with an RSD of 4.5% whereas the stability under the best conditions was 45 assays with the other supports.

Fiberoptic biosensors based on chemiluminescent reactions.

The chemiluminescence of luminol in the presence of H2O2 has been exploited to develop fiberoptic biosensors associated with flow injection analysis systems. A chlorophenol sensor was developed based on the ability of certain halophenols to enhance the peroxidase-catalyzed luminol chemiluminescence. Horseradish peroxidase immobilized on a collagen membrane was used. Ten chlorophenols have been tested with this chemiluminescent-based sensor. The lower detection limit was obtained with 4-chloro-3-methylphenol and was equal to 0.01 microM. Electrochemiluminescent-based fiberoptic biosensors for glucose and lactate were also developed using glucose oxidase or lactate oxidase immobilized on polyamide membranes. In the presence of oxidase-generated H2O2, the light emission was triggered electrochemically by means of a glassy carbon electrode polarized at +425 mV vs a platinum pseudo-reference electrode. The detection limits for glucose and lactate were 150 and 60 pmol, respectively, and the dynamic ranges were linear from 150 pmol to 600 nmol and from 60 pmol to 60 nmol, respectively.

Luminol electrochemiluminescence-based fibre optic biosensors for flow injection analysis of glucose and lactate in natural samples

A fibre optic biosensor based on the electrochemiluminescence of luminol has been developed for glucose and lactate flow injection analysis. The electrochemiluminescence of luminol was generated using a glassy carbon electrode polarised at +425 mV vs. a platinum pseudo-reference electrode. After optimisation of the reaction conditions and physicochemical parameters influencing the sensor response, the measurement of hydrogen peroxide could be performed in the range 1.5 pmol–30 nmol. Glucose oxidase or lactate oxidase, were immobilised on polyamide and collagen membranes. With collagen as the enzymatic support, the detection limits for glucose and lactate were 60 pmol and 30 pmol, respectively, whereas with the enzymatic polyamide membranes, the corresponding values were 150 pmol and 60 pmol. In each case, glucose and lactate measurements could be performed over four decades. The luminol electrochemiluminescence-based biosensors were used for glucose and lactate measurements in sera and also for lactate measurements in whey solutions. Good agreements were obtained between the present method and reference methods. For glucose analysis in serum, the coefficient of variation for 53 repeated measurements performed over a 10 h period was 4.8% while for lactate analysis, 80 assays performed over a 15 h period gave a coefficient of variation of 6.7%.

Electrochemiluminescence of luminol for 2,4-D optical immunosensing in a flow injection analysis system

Luminol-labelled antibodies have been prepared using glutaraldehyde as a cross-linking agent and used in a 2,4-dichlorophenoxyacetic acid (2,4-D) competitive electrochemiluminescent immunosensor. 2,4-D was covalently immobilized at a glassy carbon electrode surface, via a six-carbon spacer arm, by a novel procedure which allowed us to obtain stable immobilized antigens that could be then stored dry, used and regenerated 50 times without loss of binding capacity. The luminol electrochemiluminescence detection was performed in a flow injection analysis system (FIA). The optimum conditions were found to be an oxidation potential of +500 mV versus a platinum pseudo-reference electrode, in the presence of 600 μM H 2O 2. In these conditions, luminol could be detected in the range 5.5 fmol–55 nmol. Luminol-labelled anti-2,4-D antibodies or peroxidase-labelled secondary antibodies were tested for the 2,4-D immunodetection. With both the corresponding electrochemiluminescent and chemiluminescent immunoassays it was possible to detect 0.2 μg l −1 of free 2,4-D. The overall time of experiment was 50 min and a linear range from 0.2 μg l −1 to 200 mg l −1 was obtained with the peroxidase format whereas the range was 0.2–200 μg l −1 with the luminol format.

Ionic detection using differential measurement between an ion-sensitive FET and a reference FET

The possibility of obtaining ion-selective membranes on ISFETs by chemical grafting of the silica insulator has been previously shown. The grafting only slightly modifies the electrical characteristics of the transistor (the dielectric permitivity and thickness being nearly unchanged), which makes it possible to perform differential measurements between an ion-sensitive FET and a reference FET. For the detection of silver ions, the sensitive membrane (dimethylamino)silane onto silicon dioxide; the reference FET is an ISFET fabricated by grafting an aliphatic chain onto silicon dioxide. The response obtained, i.e., the difference between both source potentials versus a platinum pseudo-reference electrode, can be described with the site binding model. The differential method allows a miniaturized reference electrode to be used. At the same time, the effects of drift, temperature and residual pH response are reduced.

In Situ Formation of Polypyrrole / PEO ‐ LiCF3 SO 3 Composites by Pulsed Potentiostatic Electropolymerization

Composites of polypyrrole and were formed by in situ electropolymerization of polypyrrole at 0.8, 1.0, and 3.0V vs. a platinum pseudo reference electrode. From the current vs. time responses during electropolymerization, the initial growth of polypyrrole was found to follow the equations for three dimensional instantaneous nucleation under diffusion control at 3.0V and three‐dimensional progressive nucleation under kinetic control at 0.8V. The peak separation in solid‐state cyclic voltammograms under conditions plasticized by acetonitrile for the in situ formed polypyrrole indicate that the resistance to ion transport within the composites is lower for composites formed by pulsed potentiostatic electropolymerization at 3.0V, compared to composites grown by stepping the potential to 0.8, 1.0, or 3.0V.

Polypyrrole-PEO ∗LiCF 3SO 3 composites formed by in situ pulsed potentiostatic electropolymerization

Composites of Polypyrrole and poly(ethylene oxide) ∗LiCF 3SO 3 were formed by in situ electropolymerization of polypyrrole at 0.8, 1.0 and 3.0 V vs. a Platinum pseudo-reference electrode. The peak separation in solid state cyclic voltammograms under conditions plasticized by acetonitrile for the in situ formed polypyrrole indicate that the resistance to ion transport within the composites is lower for composites formed by pulsed potentiostatic electropolymerization at 3.0 V, compared to composites grown by stepping the potential to 0.8, 1.0 or 3.0 V.