Chlorophyll a photoelectrochemical cells with different metal electrodes

A photosensitive electrode was prepared by electrodepositing a membrane of chlorophyll a (Chla) on a SnO2 optical transparent electrode,with which and a metal counter electrode a Chla photoelectrochemical cell was formed.Photoinduced current (Ii) and photoinduced voltage (Vi) of the cell were measured.The dependence of Ii on the properties of metal electrodes was obvious,which was illustrated with mechanism of Chla photoelectrical effects Ii in this work was as high as 2×10-5 A·cm-2.     

A photosynthetic photoelectrochemical cell using phenazine methosulfate and phenazine ethosulfate as electron acceptors

Several recent studies have demonstrated that photosystem I (PSI), one of the two light-active complexes of photosynthesis, can be used as a light transducer in a biological photoelectrochemical cell. This paper examines the results of using phenazine methosulfate (PMS) and phenazine ethosulfate (PES) as an electron acceptor in such a cell. The PMS and PES have relatively high formal potentials compared to flavin mononucleotide (FMN) and other acceptors used in the past, yet the PMS and PES resulted in power outputs and conversion efficiencies second only to the use of FMN as an acceptor. The mechanism of action has been interpreted in terms of electroactive products of parent compounds formed during the normal function of the cell under illuminated conditions. For example, photolysis and cyclic voltammetry data demonstrate that pyocyanin (Py) [formal potential = -0.37 vs saturated calomel electrode (SCE) at pH 8.5], the photoproduct of PMS, is the electroactive species in cells containing PMS (formal potential = -0.19 vs SCE at pH 8.5). Similar phenomena were observed for PES and FMN. The power output of the cell results from about equal contributions from a cyclic photosynthetic component and a component caused by the direct photoreduction of the acceptor and reoxidation by sacrificial donors in the buffer. Future research directions are discussed in terms of designing cells that function purely in the photosynthetic or photochemical modes.     

Analysis of a theoretical model for anisotropic enzyme membranes application to enzyme electrodes

A theoretical model of diffusion and reaction in an anisotropic enzyme membrane is presented with particular emphasis on the application of such membranes in enzyme electrodes. The dynamic response of systems in which the kinetics are linear, which comprises the practical operating regime for enzyme electrodes in analysis, is investigated via an analytic solution of the governing differential equations. The response is presented as a function of a single dimensionless group, Μ, that is the membrane modulus.     

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 × 10⁻² to 1 × 10⁻⁶ M CPC at 25 °C over the pH range 2-8 with cationic slope 60.66 ± 1.10. The lower detection limit is found to be 8 × 10⁻⁷ M and response time of about 3 s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D. = 0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.     

Development of a biofuel cell using glucose-oxidase- and bilirubin-oxidase-based electrodes

Biofuel cells have a tremendous opportunity to provide much higher energy densities and smaller footprints than batteries for powering implantable medical devices, leading to less intrusive implantable devices with longer lifetimes. This paper introduces biofuel cell anode and cathode designs based on mediated glucose oxidation by glucose oxidase and oxygen reduction by bilirubin oxidase, respectively. We report here the progress toward the development of components for biofuel cells working in physiological conditions. We have investigated enzymatic electrode formulations that have the potential to achieve higher current densities and longer stability of the electrodes: (a) high surface area by the use of multiscale carbon materials, (b) immobilization of redox mediator on the electrode surface, and (c) use of a protective biocompatible polymer coating. Part of this work was presented at the 213th Electrochemical Society Meeting as a poster     

The microporous structure of silver/silver chloride electrodes and the implications for Harned cell operation

The stability of silver/silver chloride reference electrodes when moved between different electrolyte solutions is limited by the small amount of solution transferred. The time required for the Ag/AgCl electrode potential to stabilize has been shown to increase with electrode size in an empirical fashion. The results presented suggest the presence of a microporous structure in the electrodes that limits the rate at which traces of any previous solutions are diluted by any new solution environment. Operational implications for the stability and accuracy of the Harned Cell used as the primary standard for pH measurements and the certification of primary reference buffers are discussed. Presented to the CCQM Electrochemical Analysis Working Group, Paris, April 2004.     

Direct electrochemical assay of glucose using boron-doped diamond electrodes

We report linear sweep and square wave voltammetric studies on glucose oxidation at boron-doped diamond (BDD) electrodes in an alkaline medium in efforts to evaluate the techniques for electrochemically assaying glucose. The bare BDD electrode showed good linear responses to glucose oxidation for a concentration range from 0.5 to 10 mM glucose, which well encompasses the physiological range of 3-8 mM. The BDD electrodes did not experience interferences from ascorbic acid or uric acid during glucose detection. This method, when applied to real blood samples, gave results similar to those obtained by a commercial glucose monitor.     

Effect of surface oxygen complexes of sugar charcoal on the half cell potential of carbon-nickel ferrite electrodes

Carbon-nickel ferrite electrodes were prepared by pressing equal amounts of charcoals and nickel ferrite using ABS polymer (in acetone + benzene) as binder on a steel mesh. The half cell potentials reported were measured with reference to saturated calomel electrode. The electrolyte used was 4-N potassium hydroxide and fuel used was methanol. The surface oxygen complexes on the charcoals were varied (i) by heat-treating the sugar charcoal in vacuum at 400, 750 and 1000° C and (ii) by boiling in 4N.HNO₃ for different intervals of time. Half cell potential measured increases with the increase of oxygen content of the charcoals. The oxygen complex which is disposed off as carbon dioxide imparts polarity to the charcoal surface, and is largely responsible for the increase in potential.     

Electrochemical detection of nitric oxide using polymer modified electrodes

Electrochemical sensors based on chemical surface modification are very attractive because they combine high sensitivity of amperometry with new dimensions of selectivity and stability provided by the surface modifier. This review shows a few strategies employed to facilitate the detection, determination and monitoring of nitric oxide using polymer modified electrodes. Conducting and nonconducting polymer films and composite films are considered. The most significant achievements reached in this field, during the last decade, are critically reviewed. The collected data are also presented in three tables.     

Measuring the solubilities of ionic liquids in water using ion-selective electrodes

Polyvinyl chloride-plasticized membrane ion-selective electrodes (ISE) based on conventional ion-exchangers have been proposed as a cheap universal tool to measure the solubilities of ionic liquids (ILs) in water. They are applicable for ILs with a wide range of solubilities in water, since the linear range of a potentiometric response spans several orders of magnitude. As an example, we have fabricated and tested ISEs for widely used alkylimidazolium ionic liquids. The aqueous solubilities of four typical ILs have been determined at 21 °C: 0.075±0.001 mol l^–1 (1-butyl-3-methylimidazolium, BMIm, hexafluorophosphate); 0.018±0.001 mol l^–1 (BMIm bis(triflylimide)); 0.054±0.007 mol l^–1 (1-butyl-2,3-dimethylimidazolium, BDMIm, hexafluorophosphate); 0.014±0.001 mol l^–1 (BDMIm bis(triflylimide)).     

Morphology and photoelectrochemical properties of TiO2 electrodes prepared using functionalized plant oil binders

Chemically functionalized plant oils, viz. acrylated epoxidized soybean oil (AESO) and maleinized acrylated epoxidized soybean oil (MAESO), were used as bio-based binders for the TiO₂ electrodes of dye-sensitized solar cells (DSSC). The surface roughness and number of appropriate pores were increased in the TiO₂ films prepared using the plant oil binders in comparison with the film prepared using polyethylene glycol (PEG), due to the larger number of functionalities. The short circuit photocurrent (I_SC) and open circuit photovoltage (V_OC) were increased, and the conversion efficiency was significantly improved, in the cell using the plant oil binders.     

Potentiometric detection of organic acids in ion-exclusion chromatography using different types of liquid-membrane electrodes

Four different liquid-membrane electrodes were tested in a potentiometric flow-cell, in combination with an LC ion chromatography system (Aminex HPX-87H column). This setup was used for the determination of weak organic acids. The flow-through detector was of the wall-jet type. Conditions were established to achieve the best separation and detection characteristics. The sensitivity, selectivity and response time of the different electrodes were compared. Calibration curves and detection limits were measured for several organic acids, and compared with conductometric, and with low-wavelength UV detection. The detection limits were improved by inserting a post-column ion-suppressor system between the column and the detector. Several biological samples were analyzed to demonstrate the possibilities of the potentiometric detector.     

Convective instability of a zinc sulfate solution in a cell with horizontal plane-parallel electrodes

The Rayleigh-Bénard convective instability in a cell with horizontal zinc electrodes is considered. The space between the electrodes is filled with a ZnSO₄ solution. The linear plot of the difference between the zinc deposition currents (I) in the cases where the anode is the upper or lower electrode vs. the square root of the zinc deposition current in the absence of convection is found experimentally. It is shown that the critical Rayleigh number can be determined by an extrapolation of this plot.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 247–249.Original Russian Text Copyright © 2005 by Tomashova, Teplitskaya, Grigin, Davydov.     

Enzymatic detection of glucose using fluoride-selective electrodes with polymeric membranes

The feasibility of using polymeric membrane fluoride-selective electrodes based on zirconium(IV) 5,10,15,20-tetraphenylporphyrin as a detector in a flow-injection analysis (FIA) system for glucose determination was examined. The optimization of enzymatic reactions, FIA system configuration and enzyme-immobilization process was performed. It was shown that the resulting flow-injection system exhibits good working parameters, such as reproducibility, linear range of glucose concentration (3 × 10⁻³–10⁻¹ M), sampling rate (60 samples per minute) and lifetime (over 1 month). The performance of the polymeric membrane electrode was similar to that of a crystalline LaF₃ electrode. The results of glucose determination in synthetic samples with the proposed system show good agreement with real glucose concentrations.     

Single-drop analysis of various proteases in a cancer cell lysate using a capillary-assembled microchip

Single-drop analysis of two different real sample solutions (2 μL) while simultaneously monitoring the activity of two sets of ten different proteases on a single microfluidic device is presented. The device, called a capillary-assembled microchip (CAs-CHIP), is fabricated by embedding square glass sensing capillaries (reagent-release capillaries, RRC) in the polydimethylsiloxane (PDMS) lattice microchannel, and used for that purpose. First, the performance reliability was evaluated by measuring the fluorescence response of twenty caspase-3-sensing capillaries on a single CAs-CHIP, and a relative standard deviation of 1.5–8.2 (% RSD, n = 5 or 10) was obtained. This suggests that precise multiplexed protease-activity sensing is possible by using a single CAs-CHIP with multiple RRCs embedded. Then, using a single CAs-CHIP, real sample analysis of the activity of ten different caspases/proteases in cervical cancer (HeLa) cell lysate treated and untreated with the cell-death-inducer drug, doxorubicin, was simultaneously carried out, and a significant difference in enzyme activity between these two samples was observed. These results suggested the usefulness of the CAs-CHIP in the field of drug discovery. Figure Single drop analysis of two real sample solutions including various different proteases using a single microfluidic device was achieved     

Flow injection determination of ketotifen fumarate using PVC membrane selective electrodes

In this study a PVC membrane electrode for determination of ketotifen fumarate is reported, where ketotifen tetraphenylborate (Keto-TPB) was used as ion exchanger. The electrode has linear range of 5.6 × 10^− 6–1.0 × 10^− 2 and 1.0 × 10^− 5–1.0 × 10^− 2 mol/L, with detection limits 2.37 × 10^− 6and 4.60 × 10^− 6 mol/L in batch and flow injection analysis (FIA), respectively. The electrodes show a Nernstian slope value (58.40 and 61.50 mV/decade in batch and FIA, respectively), and the response time is very short (≤ 10 s). The potential is nearly stable over the pH range 2.0–8.0. Selectivity coefficient values towards different inorganic cations, sugars and amino acids reflect high selectivity of the prepared electrodes. These are used for determination of Ketotifen using potentiometric titration and standard addition methods in pure samples and its pharmaceutical preparations (Zaditen tablets and syrup). The average recovery values are 99.5 and 99.2% with RSD 1.4 and 1.2% for potentiometric titrations and standard addition methods, respectively. The electrode response at different temperatures was also studied.     

Anodic stripping voltammetry of antimony using gold nanoparticle-modified carbon screen-printed electrodes

Carbon screen-printed electrodes (CSPE) modified with gold nanoparticles present an interesting alternative in the determination of antimony using differential pulse anodic stripping voltammetry. Metallic gold nanoparticles deposits have been obtained by direct electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized gold nanoparticles are deposited in aggregated form. Any undue effects caused by the presence of foreign ions in the solution were also analyzed to ensure that common interferents in the determination of antimony by ASV. The detection limit for Sb(III) obtained was 9.44 × 10⁻¹⁰ M. In terms of reproducibility, the precision of the above mentioned method in %R.S.D. values was calculated at 2.69% (n = 10). The method was applied to determine levels of antimony in seawater samples and pharmaceutical preparations.     

Gas diffusion electrodes for polymer electrolyte fuel cell using sulfonated polyimide

Gas diffusion electrodes for high temperature polymer electrolyte fuel cells (PEFCs) have been prepared by using a novel proton conductive sulfonated polyimide (SPI) electrolyte. The catalyst layer was composed of Pt-loaded carbon black (Pt-CB) and SPI ionomer. The polarization properties and the microstructure of the catalyst layer were investigated as a function of the SPI/CB weight ratio. The anodic polarization was found to be negligibly small for all the compositions examined. The highest cathode performance was obtained at SPI/CB = 0.5 (by weight), where the best balance of high catalyst utilization and oxygen gas diffusion rate through the ionomer was obtained.     

Speciation of chromium using chronoamperometric biosensors based on screen-printed electrodes

Chronoamperometric assays based on tyrosinase and glucose oxidase (GOx) inactivation have been developed for the monitoring of Cr(III) and Cr(VI). Tyrosinase was immobilized by crosslinking on screen-printed carbon electrodes (SPCEs) containing tetrathiafulvalene (TTF) as electron transfer mediator. The tyrosinase/SPC_TTFE response to pyrocatechol is inhibited by Cr(III). This process, that is not affected by Cr(VI), allows the determination of Cr(III) with a capability of detection of 2.0 ± 0.2 μM and a reproducibility of 5.5%. GOx modified screen-printed carbon platinised electrodes (SPC_PtEs) were developed for the selective determination of Cr(VI) using ferricyanide as redox mediator. The biosensor was able to discriminate two different oxidation states of chromium being able to reject Cr(III) and to detect the toxic species Cr(VI). Chronoamperometric response of the biosensor towards glucose decreases with the presence of Cr(VI), with a capability of detection of 90.5 ± 7.6 nM and a reproducibility of 6.2%. A bipotentiostatic chronoamperometric biosensor was finally developed using a tyrosinase/SPC_TTFE and a GOx/SPC_PtE connected in array mode for the simultaneous determination of Cr(III) and Cr(VI) in spiked tap water and in waste water from a tannery factory samples.