A disposable amperometric sensor screen printed on a nitrocellulose strip: a glucose biosensor employing lead oxide as an interference-removing agent

A new type of disposable amperometric sensor is devised by screen printing thick-film electrodes directly on a porous nitrocellulose (NC) strip. The chromatographic NC strip is then utilized to introduce various sample pretreatment layers. As a preliminary application, a glucose biosensor based on hydrogen peroxide detection is constructed by immobilizing glucose oxidase (GOx) on the NC electrode strip and by formulating a strong oxidation layer (i.e., PbO2) at the sample loading area, placed below the GOx reaction band. The screen-printed PbO2 paste serves as a sample pretreatment layer that removes interference by its strong oxidizing ability. Samples applied are carried chromatographically, via the PbO2 paste, to the GOx layer, and glucose is catalyzed to liberate hydrogen peroxide, which is then detected at the electrode surface. The proposed NC/PbO2 strip sensor is shown to be virtually insusceptible to interfering species such as acetaminophen and ascorbic and uric acids and to exhibit good performance, in terms of the sensor-to-sensor reproducibility (standard deviation, +/-0.026 - +/-0.086 microA), the sensitivity (slope, -0.183 microA/mM), and the linearity (correlation coefficient, 0.994 in the range of 0-10 mM).     

A biotinylated conducting polypyrrole for the spatially controlled construction of an amperometric biosensor.

A new biotin derivative functionalized by an electropolymerizable pyrrole group has been synthesized. The electrooxidation of this biotin pyrrole has allowed the formation of biotinylated conducting polypyrrole films in organic electrolyte. Gravimetric measurements based on a quartz crystal microbalance, modified by the biotinylated polymer, revealed an avidin-biotin-specific binding at the interface of polymer-solution. The estimated mass increase corresponded to the anchoring of 1.5 avidin monolayers on the polypyrrole surface. In addition, the subsequent grafting of biotinylated glucose oxidase was corroborated by electrochemical permeation studies. Enzyme multilayers composed of glucose oxidase or polyphenol oxidase were elaborated on the electrode surface modified by the biotinylated polypyrrole film. The amperometric response of the resulting biosensors to glucose or catechol has been studied at +0.6 or -0.2 V vs SCE, respectively.     

Redox flow batteries based on insoluble redox-active materials.A review

The ever-increasing demand for energy has stimulated the development of economical non-fossil fuels.As representative of clean energy,solar and wind have been identified as the most promising energy sources due to their abundance,cost efficiency,and environmental friendliness.The intrinsic intermittent of the clean energy leads to the urgent requirements large-scale energy storage technique.Redox flow batteries(RFBs)are attractive technology due to their independent control over energy and power.Insoluble redox-active flow battery is a new type of electrochemical energy storage technology that disperses redox-active particles in the electrolyte.Compared with traditional flow batteries,insoluble flow batteries have advantages of large energy density and are very promising in the development of large-scale energy storage systems.At present,three types of insoluble flow batteries have been explored:slurry-based flow batteries,metal/slurry hybrid,and redox-mediator-assisted flow batteries.This Review summarizes the research progress of insoluble flow batteries,and analyzes the key challenges from the fundamental research and practical application perspectives.     

Performance of an amperometric biosensor for the determination of hemoglobin

Hemoglobin is a very important physiological index in human blood, especially for the evaluation of the physical performance of athletes. This paper reports an amperometric biosensor for the determination of blood hemoglobin, using potassium ferricyanide as a mediator, based on thin-film technology in a two-electrode system. The biosensor can be used for the determination of hemoglobin at concentrations in a linear range of 10-3000 microM, and the correlation coefficient is 0.996, the relative standard deviation is 2.3% for six determinations for 2000 microM hemoglobin concentration. And the linear range of hemoglobin is studied using methylene blue as a mediator.     

Enzyme-catalyzed O2 removal system for electrochemical analysis under ambient air: application in an amperometric nitrate biosensor

Electroanalytical procedures are often subjected to oxygen interferences. However, achieving anaerobic conditions in field analytical chemistry is difficult. In this work, novel enzymatic systems were designed to maintain oxygen-free solutions in open, small volume electrochemical cells and implemented under field conditions. The oxygen removal system consists of an oxidase enzyme, an oxidase-specific substrate, and catalase for dismutation of hydrogen peroxide generated in the enzyme catalyzed oxygen removal reaction. Using cyclic voltammetry, three oxidase enzyme/substrate combinations with catalase were analyzed: glucose oxidase with glucose, galactose oxidase with galactose, and pyranose 2-oxidase with glucose. Each system completely removed oxygen for 1 h or more in unstirred open vessels. Reagents, catalysts, reaction intermediates, and products involved in the oxygen reduction reaction were not detected electrochemically. To evaluate the oxygen removal systems in a field sensing device, a model nitrate biosensor based on recombinant eukaryotic nitrate reductase was implemented in commercial screen-printed electrochemical cells with 200 μL volumes. The products of the aldohexose oxidation catalyzed by glucose oxidase and galactose oxidase deactivate nitrate reductase and must be quenched for biosensor applications. For general application, the optimum catalyst is pyranose 2-oxidase since the oxidation product does not interfere with the biorecognition element.     

Sol-gel thin-film immobilized soybean peroxidase biosensor for the amperometric determination of hydrogen peroxide in acid medium.

An acid-stable soybean-peroxidase biosensor was developed by immobilizing the enzyme in a sol-gel thin film. Methylene blue was used as a mediator because of its high electron-transfer efficiency. The sol-gel thin film and enzyme membrane were characterized by FT-IR, and the effects of pH, operating potential, and temperature were explored for optimum analytical performance by using the amperometric method. The H2O2 sensor exhibited a fast response (5 s), high sensitivity (27.5 microA/mM), as well as good thermostability and long-term stability. In addition, the performance of the biosensor was investigated using flow-injection analysis (FIA).     

Three-dimensional microfluidic confinement for efficient sample delivery to biosensor surfaces. application to immunoassays on planar optical waveguides

A microchip-based flow confinement method for rapid delivery of small sample volumes to sensor surfaces is described. For flow confinement, a sample flow is joined with a perpendicular makeup flow of water or sample medium. Under laminar flow conditions, the makeup flow confines the sample into a thin layer above the sensing area and increases its velocity. This can benefit mass transport limited processes such as DNA hybridization or heterogeneous immunoassays. For proof of concept, this method was applied to a high-affinity immunoassay with excess capture antibody. Rabbit IgG was immobilized onto a silicon nitride waveguide. Cy5-labeled anti-rabbit IgG was hydrodynamically pumped over the immobilized zone through an attached 3D-PDMS flow cell with 20-microm-deep microchannels. The degree of confinement was adjusted through the volume flow rate of the confining flow. Evanescent field-based fluorescence detection enabled monitoring of the binding event. Assays were allowed to reach equilibrium to enable sensorgram normalization for inter-run comparison. The corresponding assay completion times could be reduced from 55 min for static drop conditions to 13 min for 25:1 flow confinement (ratio of confining to sample flow). For typical analytical applications, where equilibrium formation is not required, the faster response should translate to very short analysis times. Concurrently with the faster binding, sample consumption was reduced by 96% compared to conventional whole-channel sample delivery. Diffusional loss of analyte into the confining layer was identified as the main limitation of flow confinement, particularly for long sensing pads.     

Polymeric reagents. IX Use of a polysterene-based amine oxide as a regenerable oxidizing agent for alkyl halides

A new polymeric reagent based on a crosslinked polysterene matrix modified to incorporate tertiary amine oxide residues is useful in the oxidation of primary alkyl bromides, alkyl iodides or benzylic halides into aldehydes. In all cases the yields are excellent and no overoxidation to form carboxylic acid is observed. The polymeric reagent can also be used to oxidize secondary alkyl bromides and iodides to the corresponding ketones, but these reactions are accompanied by significant side reactions which produce undersired alkenes. Unlike the corresponding low-molecular-weight reagents such as trimethylamine N-oxide, the polymer can be easily freed from impurities which cause significant side-reactions and does not require the use of scrupulously anhydrous reaction conditions for oxidation to occur. As expected, the use of the polymeric reagent also results in a simpler processing of the reaction mixtures, with filtration and evaporation of solvent as the isolation steps. The polymeric by-product of the reaction can be recovered quantitatively and be regenerated after washing, by treatment with hydrogen peroxide. The regenerated reagent is as effective an oxidizing agent as the starting polymer, and no significant loss of activity is observed after five reaction cycles.     

Precipitation of an insoluble product on enzyme monolayer electrodes for biosensor applications: characterization by Faradaic impedance spectroscopy, cyclic voltammetry, and microgravimetric quartz crystal microbalance analyses.

Precipitation of an insoluble, insulating product on monolayer-functionalized electrodes enables the development of new electrochemical biosensors. Faradaic impedance spectroscopy and cyclic voltammetry are used to probe the electron-transfer resistance at the conductive support upon the accumulation of the insoluble product on the electrode surface. Similarly, microgravimetric quartz crystal microbalance, QCM, analyses were used to assay the formation of the precipitate on the electrode. A horseradish peroxidase, HRP, monolayer electrode is used to analyze H2O2 via the biocatalyzed oxidation of 4-chloro-1-naphthol (1) and the precipitation of the insoluble product (2). A bienzyme-layered electrode consisting of HRP and glucose oxidase, GOx, is used to sense glucose. Biocatalyzed oxidation of glucose by O2, in the presence of GOx, yields H2O2, and the generated hydrogen peroxide effects the formation of the insoluble product (2) in the presence of HRP. The insoluble product accumulated on the electrode, and the extent of the resulting electron-transfer resistance, correlated with the amounts of H2O2 or glucose, and appropriate calibration curves are extracted.     

A microscale biosensor for methane containing methanotrophic bacteria and an internal oxygen reservoir

A microscale biosensor for continuous measurement of methane partial pressure based on a novel counterdiffusion principle is presented. Methane-oxidizing bacteria placed in the microsensor utilize oxygen from an internal oxygen reservoir when methane from the exterior diffuses through the tip membrane. The transducer is an internal oxygen microsensor with its tip positioned between the oxygen reservoir and the sensor tip membrane. The external partial pressure of methane determines the rate of bacterial oxygen consumption within the sensor, which in turn is reflected by the signal from the transducer. Tip diameters were down to 20 μm, enabling us to study methane distribution on a microscale. The microscale construction also results in a low stirring sensitivity and a 95% response time down to 20 s. By tailoring the geometry, sensors can be made to exhibit a linear response in the full range of 0-1 atm partial pressure of methane or, alternatively, to exhibit a linear response only at lower concentrations, improving the sensitivity to below 0.1 kPa, corresponding to ～1 μM in aqueous solution. Temperature, oxygen, and H(2)S interfere with the signal; no interferences were detected from H(2), NH(3), CO(2), or acetate.     

A biomimetic phospholipid/alkanethiolate bilayer immobilizing uricase and an electron mediator on an Au electrode for amperometric determination of uric acid.

A biomimetic bilayer membrane immobilizing uricase (urate oxidase; EC 1.7.3.3) (UOx) and a redox agent of 1-methoxy-5-methylphenazinium (MMP) was fabricated on an Au electrode substrate with use of the Au substrate coated with a self-assembled monolayer of n-octanethiolate (OT/Au) and L-alpha-phosphatidylcholine beta-oleoyl-gamma-palmitoyl (PCOP). The preparation was carried out by successively immersing an Au electrode substrate in an ethanol solution of OT, an MMP aqueous solution, and a suspension of proteoliposome formed by PCOP containing UOx and MMP. The prepared electrode exhibited such fast steady amperometric responses to uric acid as to allow its determination within 20 s after injecting uric acid, indicating that UOx-catalyzed electrochemical oxidation of uric acid was accomplished with assistance of electron mediation by MMP between UOx and the Au substrate. An increase in the response currents with increasing concentration of uric acid was obtained in a concentration range of uric acid found in healthy human blood. Any interference in the current response that is caused by direct anodic oxidation of uric acid or ascorbic acid was not observed at the prepared sensor electrode because the densely packed bilayer effectively blocked the diffusion of these substrates toward the Au surface, making it possible to determine amperometrically uric acid at the electrode with high precision.     

A boundary formulation for calculating moments of an arbitrary closed planar region

In this study, a boundary formulation for calculating moments of an arbitrary closed planar region is proposed instead of calculating moments using the domain integral. The Gauss’ divergence theorem is used to transform moments of area into boundary integrals. Three examples are demonstrated to show the validity of the proposed method. Results obtained from the boundary formulation are compared with analytical solutions, and good accuracy is obtained.     

Improved planar amperometric nitric oxide sensor based on platinized platinum anode. 1. Experimental results and theory when applied for monitoring NO release from diazeniumdiolate-doped polymeric films

An improved miniature amperometric nitric oxide sensor design with a planar sensing tip (ranging from 150 microm to 2 mm in diameter) is reported. The sensor is fabricated using a platinized platinum anode and a Ag/AgCl cathode housed behind a microporous poly(tetrafluoroethylene) (PTFE; Gore-tex) gas-permeable membrane. Platinization of the working platinum electrode surface dramatically improves the analytical performance of the sensor by providing approximately 10-fold higher sensitivity (0.8-1.3 pA/nM), approximately 10-fold lower detection limit (< or =1 nM), and extended (at least 3-fold) stability (>3 d) compared to sensors prepared with bare Pt electrodes. These improvements in performance arise from increasing the kinetics and lowering the required potential for the 3-electron oxidation of NO to nitrate, relative to that observed using a nonplatinized working electrode. The outer porous PTFE membrane provides complete selectivity for NO over nitrite ions (up to 10 mM nitrite). The new sensor is applied for surface measurements of NO released from diazeniumdiolate-loaded silicone rubber films (SR-DACA-6/N(2)O(2)). The effects of sensor size (for sensor dimensions of 0.15-, 1-, and 2-mm o.d.) and the distance of the sensor from the surface of the NO-emitting polymer film are investigated via experiments as well as theoretical calculations. A significant analyte trapping effect is demonstrated, the degree of which depends on the sensor size and its distance from the surface. It is further demonstrated that surface NO concentrations for fresh SR-DACA-6/N(2)O(2) loaded films are also influenced by the polymer film thickness, with thicker films generating higher surface concentrations of NO.     

Identification and optimization of regeneration conditions for affinity-based biosensor assays. A multivariate cocktail approach.

A general regeneration, identification, and optimization (RO) protocol for Biacore systems was developed. The RO protocol uses six multi-ingredient stock solutions that represent the six most common chemical properties employed as regeneration agents. The regeneration effect of different regeneration cocktails of these six stock solutions were tested iteratively until a satisfactory result was obtained. The RO protocol was designed with an ease-of-use and multivariate approach. The RO protocol was tested on 13 different antibody-antigen systems. For 10 of these, only the first screening session was tested. For 9 of the 13 systems, the RO-protocol screening session identified cocktails that removed more than 90% of the bound analyte in a 30 s pulse. For 5 systems, the RO protocol identified cocktails that regenerated the surface completely and that were more gentle than previously used regeneration conditions. Furthermore, the regeneration optimization results can be interpreted as a characterization of the interacting molecules. The relevance of testing cocktails was justified by the fact that at least one cocktail was significantly better than all diluted stock solutions for all tested model systems. By using the multivariate approach, the risk of missing relevant combinations of stock solutions was minimized. This resulted in an unexpected discovery of excellent properties of EDTA as an additive in regeneration cocktails containing chaotropic agents and ions in high concentration.     

Preformulation studies for an ultrashort-acting neuromuscular blocking agent GW280430A. I. Buffer and cosolvent effects on the solution stability

GW280430A is an ultrashort-acting neuromuscular blocking agent targeted at muscle relaxation to facilitate surgical intubation. The objective of this work was to study the buffer and cosolvent effects on the solution stability of GW280430A. The buffer catalytic effect was examined in citrate, malate, tartrate, and glycine by measuring the rate of degradation of GW280430A (0.2 mg/mL) at constant pH (3), ionic strength (0.15 M), and various buffer concentrations (0.01-0.05 M). The temperature dependence of the buffer catalytic effect and the degradation of the GW280430A in cosolvent (ethanol, propylene glycol, polyethylene glycol 400, N,N-dimethylacetamide)/water mixtures were studied at 40, 50, and 60°C. The loss of parent drug was monitored by reverse-phase high-performance liquid chromatography. The degradation of GW280430A followed first-order kinetics in all buffer solutions. Significant buffer-catalyzed hydrolysis of GW280430A was observed with citrate, tartrate, and malate buffers, but not in glycine-buffered solutions. The activation energies in all buffered drug solutions ranged from 70 to 80 kJ/mol and decreased with increasing buffer concentration. GW280430A degradation was primarily through ester hydrolysis and followed first-order kinetics in aqueous solutions. In cosolvent/water mixtures, new degradation products were observed, indicating a chemical reaction between GW280430A and cosolvents. The reaction activation energies in the cosolvent/water mixtures ranged from 75 to 85 kJ/mol, with the longest t_0.9 at 5°C equal to approximately 12 months and at 25°C equal to 36 days. Consideration should be given to the incorporation of glycine or a low concentration of citrate, malate, or tartrate buffer in the parenteral formulation development of GW280430A. Cosolvents prolonged the predicted t_0.9 for GW280430A in solution, but the enhancement was not significant enough to pursue a liquid formulation.     

8. A specimen-exchange device for an ultra-high vacuum atom-probe field-ion microscope

A specimen-exchange device is described for an ultra-high vacuum field-ion microscope (FIM). This device completely eliminates the long pump-down period that is required if the FIM chamber is brought back to atmospheric pressure. The pressure in an air-lock is reduced to 10^?6 torr before the exchange takes place and the pressure in the FIM chamber remains below 10^?7 torr during the exchange and it drops to less than 3 × 10^?9 torr within 15 min after the exchange.     

Charts for an empire. A global trading zone in early modern Portuguese nautical cartography

The global phenomenon of maritime expansion and the measures of control imposed by the interventionism of the Iberian crowns generated a context that sheds light on the Zilselian issue: the contact between artisans and university‐trained men in early modern Europe. This is an old and controversial topic. However, this article does not focus solely on the economic and social reasons for this contact, but also on epistemological and political motivations. With the specific aim of illustrating this collaboration, the article analyses some of the empirical practices developed under the Portuguese maritime empire throughout the 16th century. This is achieved through the reconstruction of the process of production of nautical charts in the Armazéns da Guiné e Índia (Storehouse of Guinea and Indies) of Lisbon, which I consider a large‐scale “trading zone.” This reconstruction throws light not only on the technical complexity of these cognitive processes and the coordinated work of the different agents involved in their production, but also on the emergence of new spaces of knowledge and new communities of practitioners (with new professional statuses) linked to them; new methods of collection and management of information; and, finally, new forms of circulation and standardization of knowledge in the early modern period.