Development of an On-line Glucose Sensor for Fermentation Monitoring

A dimethylferrocene-mediated enzyme electrode for glucose (Cass et al., 1984) was evaluated for application to microbial fermentation monitoring and control. The deficiencies revealed - insufficient stability, progressive increase in response time and progressive decrease in linear range - were investigated using electrochemical and radiochemical techniques. The enzyme immobilization was improved with a novel procedure using periodate-oxidized glucose oxidase and an alky lamine electrode coating. An in-situ probe and a computer-controlled analytical system were developed for fermentation monitoring. The glucose concentration of an Escherichia coli batch culture was successfully monitored on line using this analytical system.     

Microbore high-performance liquid chromatographic method for measuring acetylcholine in microdialysis samples: optimizing performance of platinum electrodes

A microbore high-performance liquid chromatographic method with electrochemical detection was applied to the measurement of acetylcholine in microdialysis samples. There was an excellent linear relationship (r=0.99998) between the concentration of acetylcholine injected onto the column and the peak height (0.05–10 pmol/5 μl). During the validation of this method, we noticed that the peak height for acetylcholine decreased over time, coupled with the appearance of a brown coating on the surface of the platinum electrode. Repeated measurement of acetylcholine standards which had been stored at 4°C and −20°C before and after cleaning the platinum electrode with ethanol or methanol indicated that the decrease in the peak height of acetylcholine is caused by a decrease in sensitivity of the electrode itself. Results with a second microbore high-performance liquid chromatographic system confirmed these findings. On the basis of these results, we recommend that the platinum electrode is cleaned periodically with ethanol or methanol, and that quantitation is regularly calibrated with external acetylcholine.     

聚3，4乙烯二氧噻吩修饰的新型碳纳米管纤维电极及其电化学性能评价

目的 植入式脑机接口在神经疾病的治疗方面已经得到了广泛应用，治疗的效果依赖于与神经组织接触的电极。与刚性材料制作的电极相比，碳基微纤维电极尺度小、生物兼容性好、组织炎症反应小，可以减少植入后的异物反应，改善神经记录信号的信噪比，可以长期保持稳定的电极特性。方法 本文设计了一种柔性碳纳米管（carbon nanotubes，CNTs）纤维电极的修饰方法，该方法采用电化学聚合的方式可以将聚3,4-乙烯二氧噻吩（poly（3,4-ethylenedioxythiophene），PEDOT）薄膜沉积到CNTs纤维电极上，作为微电极涂层。为了证明修饰涂层在电极表面具有良好的机械稳定性，对修饰电极进行了超声处理。此外，本文将PEDOT薄膜沉积到ITO玻璃上，评价了PEDOT薄膜的生物相容性。结果 恒电流方式在CNTs纤维电极表面沉积的PEDOT涂层降低了电极的电化学阻抗，提高了电极的电化学性能，且PEDOT沉积的时间越长阻抗减少的幅度越明显。对电极进行超声处理后，电极的电化学阻抗没有产生显著变化，说明超声处理后PEDOT涂层剥离较少，证明了修饰涂层在电极表面具有良好的机械稳定性。最后，细胞实验表明，PEDOT薄膜具有与ITO导电玻璃相当的细胞相容性。结论 PEDOT薄膜可以提高CNTs纤维电极的稳定性，有望提高脑机接口系统的寿命和可靠性，具有应用于长时间记录神经电信号的前景。     

Upscaling of Perovskite Solar Cells: Fully Ambient Roll Processing of Flexible Perovskite Solar Cells with Printed Back Electrodes

A scaling effort on perovskite solar cells is presented where the device manufacture is progressed onto flexible substrates using scalable techniques such as slot‐die roll coating under ambient conditions. The printing of the back electrode using both carbon and silver is essential to the scaling effort. Both normal and inverted device geometries are explored and it is found that the formation of the correct morphology for the perovskite layer depends heavily on the surface upon which it is coated and this has significant implications for manufacture. The time it takes to form the desired layer morphology falls in the range of 5–45 min depending on the perovskite precursor, where the former timescale is compatible with mass production and the latter is best suited for laboratory work. A significant loss in solar cell performance of around 50% is found when progressing to using a fully scalable fabrication process, which is comparable to what is observed for other printable solar cell technologies such as polymer solar cells. The power conversion efficiency (PCE) for devices processed using spin coating on indium tin oxide (ITO)‐glass with evaporated back electrode yields a PCE of 9.4%. The same device type and active area realized using slot‐die coating on flexible ITO‐polyethyleneterphthalate (PET) with a printed back electrode gives a PCE of 4.9%.     

Electrochemical study of the XNA on Gold microarray

A novel electrode array was developed based on the XNA on Gold trade mark microarray platform. The platform combines self-assembling monolayers, thick film patterning and streptavidin based immobilization to provide a robust, versatile platform capable of analysing virtually any biomolecule including nucleic acids, proteins, carbohydrates and lipids. Electrochemical analysis of the self-assembling monolayer/streptavidin (SAMS) XNA on Gold coating revealed that the ferrocene redox current for the SAMS modified electrode was greater than that with a bare Gold electrode. The electrochemical reaction of K4Fe(CN)6 was inhibited by the SAMS coating, but was reactivated upon addition of ferrocene. These results indicate that ferrocene is involved as a mediator in the electron transfer of K4Fe(CN)6 to the SAMS modified electrode. Addition of DNA to the SAMS resulted in only a minor change in the electrochemical signal, indicating that XNA on Gold can be used for electrochemical based bioanalysis. After cycling a SAMS electrode 50 times, no signs of deterioration were detected showing that coating has excellent stability. In addition to the biosensing applications, the scheme provides a non-invasive method for accessing the quality of the SAMS coatings which is of industrial interest. These studies show that the XNA on Gold microarray platform can be used for electrochemical studies, thus providing an additional alternative for developing multianalyte biosensors as well as expanding the range of detection methods available for microarray analysis.     

Unexpected Improved Performance of ALD Coated LiCoO2/Graphite Li‐Ion Batteries

The performance of Al₂O₃ atomic layer deposition (ALD) coatings for LiCoO₂/natural graphite (LCO/NG) batteries is investigated, where various permutations of the electrodes are coated in a full battery. Coating both electrodes with ～1 nm of alumina as well as coating only the LCO (positive electrode) enables improved performance when cycling at high voltage, where the LCO is known to degrade. However, we found that coating only the NG (negative electrode) also improves the performance of the whole battery when cycling at high voltage. Under these conditions, the uncoated LCO (positive electrode) should degrade quickly, and the NG should be unaffected. A variety of characterization techniques show the surface reactions that occur on the negative electrode and positive electrode are related, resulting in the enhanced performance of the uncoated LCO.     

Biocompatible glucose sensor prepared by modifying protein and vinylferrocene monomer composite membrane

This paper proposes a very simple procedure for preparing a biocompatible sensor based on a protein (bovine serum albumin, BSA), enzyme and vinylferrocene (VF) composite membrane modified electrode. The membrane was prepared simply by first casting vinylferrocene and then coating it with BSA and glucose oxidase immobilised with glutaraldehyde. The sensor response was independent of dissolved oxygen concentration from 3 to 10 ppm and showed good stability for serum sample measurement, unlike the commonly used BSA/enzyme modified electrode. The sensor response was almost unchanged over the measurement time (>10 h) whereas the responses of a BSA and glucose oxidase modified platinum electrode and an osmium-polyvinylpyridine wired horseradish peroxidase modified electrode (Ohara et al., 1993) fell to 68% of their initial value in a serum sample containing 10mM glucose.     

Development of a micro-planar amperometric bile acid biosensor for urinalysis

The determination of bile acid concentration in urine is useful for the screening and diagnosis of various hepatobiliary diseases. Currently, there is no concise method to determine bile acid concentration in urine. This study describes a bile acid biosensor fabricated by electrochemical technique for urinalysis. The micro-planar electrodes employed for the study consisted of a working electrode (platinum), a counter electrode (platinum) and a reference electrode (silver/silver chloride (Ag/AgCl)). The sensor chip was coated with Nafion using a spin-coater in order to both eliminate many interference species in urine and achieve long-term stability of the reference electrode. Nafion coating allowed the sensor chip to prevent the electrode reaction from interference species in urine, because it is charged negative strongly (Nafion contains sulfonic acid group). Three enzymes (bile acid sulfate sulfatase: BSS, beta-hydroxysteroid dehydrogenase: beta-HSD, and NADH oxidase: NHO) were immobilized by glutaraldehyde (GA: cross-linker) onto the sensor chip, because the immobilization of enzymes by GA is simple and commonly carried out. The sensor chip was able to detect bile acid in buffer solution. The optimum enzyme ratio immobilized onto the sensor chip was BSS:beta-HSD:NHO=4:4:20 U/1 chip. There was a relationship between the concentration of bile acid and the response current value. The dynamic range of the sensor chip was 2-100 microM for bile acid. Additionally, bile acid in the urine specimen could be detected using this bile acid biosensor. We present a simple and rapid bile acid biosensor with high sensitivity and high reproducibility.     

Glutathione (GSH) Determination by a Very Simple Electrochemical Method

Glutathione (GSH; gamma-glutamylcysteinylglycine) is ubiquitous in mammalian and other living cells. It contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side chain. It has several important functions, including protection against oxidative stress. It is synthesized from its constituent amino acids by the consecutive actions of gamma-glutamylcysteine synthetase and GSH synthetase. Cellular levels of GSH may be increased by supplying substrates and GSH delivery compounds. Increasing cellular GSH may be therapeutically useful. In this study, we investigated the applicability of the glassy carbon electrode coated with thin Hg film layer to the determination of reduced glutathione (GSH). For this purpose, firstly, Hg coating process parameters were studied such as concentration of mercury coating solution, coating current, coating temperature. Then, working conditions were investigated. At the end of these studies, we concluded that although some of limitations, the sensor would be applicable to the determination of reduced glutathione.     

Ion-exchange voltammetry and electrocatalytic sensing capabilities of cytochrome c at polyestersulfonated ionomer coated glassy carbon electrodes

The incorporation and electrochemical behaviour of cytochrome c (Cyt C) at glassy carbon electrodes modified with the polyestersulfonated ionomer Eastman AQ 55 are examined. The presence of the polyelectrolytic coating allows the preconcentration of the protein within the polymer and the observation of the direct electrochemistry of Cyt C at the modified electrode without addition of promoters or mediators in the solutions. The dependence of voltammetric signals on typical parameters such as solution pH and nature or concentration of the supporting electrolyte supports the ion-exchange nature of the incorporation process. The relevant role of the permselectivity of the polymeric modifier is highlighted also by the study of electrocatalytic processes which take place at the modified electrode loaded with Cyt C. No electrocatalytic effect is observed when the electrogenerated dication (ferricenylmethyl)trimethylammonium is present as possible oxidant. On the contrary, electrocatalytic current enhancements are observed for anionic substrates such as Fe(CN)(6)(3-) (oxidant) and ascorbate (reductant). Catalytic currents increase with the substrate concentration, with higher sensitivity for Fe(CN)(6)(3-). Due to ionic repulsion, the reaction with anions occurs at the polymer-solution interface. In the case of chemically unstable substrates, such as superoxide anion, ionic repulsion slow down the approach rate of the substrate so that spontaneous decomposition can prevail over the reaction with Cyt C incorporated in the coating.     

Immobilization of invertase in polyvinyl alcohol coatings

A possibility of invertase immobilization in the polyvinyl alcohol coating formed directly on the electrode surface from water solution of polyvinyl alcohol and boric acid was being investigated. Conditions for obtaining the polymeric coating at the constant potential and at the constant current were compared. In order to obtain the polymeric coatings with a marked enzyme activity optimal conditions were found.     

Photomicrobial electrode for selective determination of sulphide

Summary A photomicrobial electrode, which uses the photosynthetic bacteria Chromatium sp. in conjunction with a hydrogen electrode, was developed for the determination of sulphide. The response time of the photomicrobial electrode was 5–10 min. A linear relationship was obtained between the current of the electrode and the sodium sulphide concentration below 3.5 mM. The minimum detectable concentration of sodium sulphide was 0.4 mM. Selectivity of the sensor is satisfactory. A good agreement was obtained between the photomicrobial electrode and the ethylene blue method (correlation coefficient: 0.90).     

Enhanced Stability of Coated Carbon Electrode for Li‐O2 Batteries and Its Limitations

Li‐O₂ batteries are promising next‐generation energy storage systems because of their exceptionally high energy density (≈3500 W h kg^?1). However, to achieve stable operation, grand challenges remain to be resolved, such as preventing electrolyte decomposition and degradation of carbon, a commonly used air electrode in Li‐O₂ batteries. In this work, using in situ differential electrochemical mass spectrometry, it is demonstrated that the application of a ZnO coating on the carbon electrode can effectively suppress side reactions occurring in the Li‐O₂ battery. By probing the CO₂ evolution during charging of ¹³C‐labeled air electrodes, the major sources of parasitic reactions are precisely identified, which further reveals that the ZnO coating retards the degradation of both the carbon electrode and electrolyte. The successful suppression of the degradation results in a higher oxygen efficiency, leading to enhanced stability for more than 100 cycles. Nevertheless, the degradation of the carbon electrode is not completely prevented by the coating, because the Li₂O₂ discharge product gradually grows at the interface between the ZnO and carbon, which eventually results in detachment of the ZnO particles from the electrode and subsequent deterioration of the performance. This finding implies that surface protection of the carbon electrode is a viable option to enhance the stability of Li‐O₂ batteries; however, fundamental studies on the growth mechanism of the discharge product on the carbon surface are required along with more effective coating strategies.     

Electrochemical prevention of marine biofouling on a novel titanium-nitride-coated plate formed by radio-frequency arc spraying

We have developed a new method for forming titanium-nitride(TiN)-coated plates using radio-frequency arc spraying (RFAS). A TiN coating formed by RFAS has been used for electrochemical prevention of marine biofouling. X-ray diffraction and X-ray photoelectron spectroscopy indicate that a TiN composite film containing Ti was formed on a polyethylene terephthalate plate surface when Ti was sprayed by RFAS under atmospheric pressure. A cyclic voltammogram (scan rate 20 mV/s) of the TiN formed by RFAS revealed no oxidative and reductive peak currents in the range −0.6 V to 1.2 V against a saturated silver/silver chloride (Ag/AgCl) electrode. When a potential of 1.0 V against Ag/AgCl was applied to the electrode in seawater, no dissolved Ti was detected. Changes in pH and the chlorine concentration were not observed in this range. In all, only 4.5% of the Vibrio alginolyticus cells attached to the electrode survived when a potential of 0.8 V against Ag/AgCl was applied in seawater for 30 min. In field experiments, attachment of the organisms to the TiN electrode was inhibited by applying an alternating potential of 1.0 V and −0.6 V against Ag/AgCl. The TiN film can be formed by RFAS on large and intricately shaped surfaces, and it is a practical electrode for the electrochemical prevention of fouling of various marine structures. Received: 17 April 1998 / Received revision: 5 June 1998 / Accepted: 19 June 1998     

Synthesis of 7-Desoxypanepoxydol

Glucose oxidase was immobilized on the surface of a p-benzoquinone-carbon paste electrode by coating the enzyme-loaded surface with a nitrocellulose film. The electrode was able to oxidize glucose electrocatalytically. It showed high current response to glucose, and was stable for more than a week. The electrode can be used as a glucose sensor that is relatively insensitive to variations of oxygen tension in sample solutions.     

Electrolytic regeneration of NADH from NAD with a liquid crystal membrane electrode

Enzymatically active NADH was electrolytically regenerated from its oxidized from (NAD⁺) with a liquid crystal membrane electrode made by coating a hanging drop or a pool type of mercury electrode with a cholesteryl oleate membrane which could be in the liquid crystal state. A cholesteryl oleate membrane was employed to prevent dimerization of the NAD radical supposed to be an intermediate of electrolytic reduction of NAD⁺.     

Determination of substrate concentrations by a computerized enzyme electrode

A numerical treatment of the signal produced by an electrode onto which an artificial enzyme membrane is mounted can give the concentration of the substrate (glucose, saccharose, lactose, amino acids, etc.) in solution. In the example of a glucose analyzer, in which glucose oxidase catalyzes the oxidation of glucose, the computer receives pO(2) level data from the electrode and calculates the glucose concentration. The transient electrode signal, measured as the enzyme membrane is exposed to a solution of glucose, is least-square approximated by a third-degree polynomial whose slope at inflection point is characteristic of the external glucose concentration. A calibration procedure provides a cubic spline approximation of glucose concentration as a function of slope, thus enabling automatic measurement of samples. The computer performs the calculations, and actuates valves for air rinsing, introduction of the sample, and water rinsing.     

Potentiometric determination of cysteine with thiol sensitive silver-mercury electrode

A potentiometric procedure for cysteine thiol group concentration monitoring in media generating free radicals was developed using a thiol specific silver-mercury electrode. Electrolytic deposition of mercury on a silver wire and treatment with 20 mM cysteine in 0.5 M NaOH were used to produce the electrode. A silver-chloride electrode in saturated KCl was the reference. A glass capillary with 1 M KNO3 in 1% agarose gel was the liquid junction. The electrode responded to cysteine concentration in the range from 0.01 to 20 mM yielding a perfect linear relationship for the dependence of log [cysteine] versus electrode potential [mV], with b0 (constant) = -373.43 [mV], b1 (slope) = -53.82 and correlation coefficient r2 = 0.97. The electrode potential change per decade of cysteine concentration was 57 mV. The minimal measurable signal response was at a cysteine concentration of 0.01 mM. The signal CV amounted to 4-6% for cysteine concentrations of 0.01 to 0.05 mM and to less than 1% for cysteine concentrations of 0.5 to 20 mM. The response time ranged from about 100 s for cysteine concentrations of 0.01 to 0.1 mM to 30 s at higher cysteine concentrations. The standard curve reproducibility was the best at cysteine concentrations from 0.1 to 20 mM. In a reaction medium containing cysteine and copper(II)-histidine complex ([His-Cu]2+) solution in 55 mM phosphate buffer pH 7.4 the electrode adequately responded to changes in cysteine concentration. Beside cysteine, the silver-mercury electrode responded also to thiol groups of homocysteine and glutathione, however, the Nernst equation slope was about half of that for cysteine.     

Three‐Dimensional Nanostructured Indium‐Tin‐Oxide Electrodes for Enhanced Performance of Bulk Heterojunction Organic Solar Cells

A three‐dimensional indium tin oxide (ITO) nanohelix (NH) array is presented as a multifunctional electrode for bulk heterojunction organic solar cells for simultaneously improving light absorption and charge transport from the active region to the anode. It is shown that the ITO NH array, which is easily fabricated using an oblique‐angle‐deposition technique, acts as an effective antireflection coating as well as a light‐scattering layer, resulting in much enhanced light harvesting. Furthermore, the larger interfacial area between the electrode and the active layer, together with the enhanced carrier mobility through highly conductive ITO NH facilitate transport and collection of charge carriers. The optical and electrical improvements enabled by the ITO NH electrode result in a 10% increase in short‐circuit current density and power‐conversion efficiency of the solar cells.     

The calibration and use of a calcium ion-specific electrode for kinetic studies of mitochondrial calcium transport.

A calcium ion-specific electrode has been used to study calcium transport by isolated,hepatic mitochondria. The methodology used requires only a sensitive pH meter operated in the millivolt mode with the electrode. Free calcium ion concentrations may be followed continuously. Using incubation conditions which cause release of intramitochondrial calcium, the calcium electrode system may also be used to determine total. intramitochondrial calcium. Techniques for the calibration of the electrode response are discussed. Free calcium ion concentrations have been calculated from total calcium concentrations and the association constants for the binding species present in the assay medium. The observation that the electrode response is linear to submicromolar concentrations allows calculation of a linear least-squares fit of millivolt reading to computed free calcium ion concentration. A computer program written in BASIC for these computations is included in Appendix material. The half-maximal rate constant for mitochondrial calcium uptake has been found to occur at a free calcium ion concentration of 6.5 μm. The interaction or Hill coefficient for the process is 2.3, indicating positive cooperativity.