A regenerable pseudo-reagentless glucose biosensor based on Nafion polymer and l,1''-dimethylferricinium mediator

Glucose oxidase was immobilized onto electrodes by co-deposition from an aqueous solution containing the diluted ion-exchange polymer Nafion. The cationic exchange property of the polymer was used to provide high local concentrations of l,1'-dimethylferricinium (DMFc⁺) mediator in the film by exchange from solution. The mediated electrodes were operated at +200 mV (vs. ), and the Nafion film was shown to reduce interfering current from ascorbate anion. Cyclic voltammetric analysis revealed a fourteen-fold increase in the effective DMFc⁺ activity at the electrode after extraction into the film. The sensitivity to glucose was 52 μA/cm²/mM in a solution containing 0.09 mM DMFc⁺, which is at least three-fold greater than reported for similar electrodes using hydrogen peroxide detection at +650 mV, with a response time of less than 1 min for a 10 μm thick membrane. Oxygen interference was significant, requiring deaeration of the solution before analysis. The electrodes exhibited no significant decrease in sensitivity for more than 50 days on storage in acetate buffer. Electrodes covered with 8000 MWCO dialysis membrane slowed the exchange of DMFc⁺ with the solution such that the Nafion film functioned as a mediator reservoir. This permitted reagentless analysis of glucose, typically capable of twenty assays when measuring concentrations between 0.1 and 1 mM. The sensitivity for glucose was 7.85 μA/cm²/mM, which is 15% of the sensitivity for the electrode without the dialysis membrane. The detection limit was 20 μM, with a linear range extending to about 3 mM, giving a dynamic range of over two orders of magnitude. Thus where some sacrifice of sensitivity and response rate may be made, the dialysis membrane cover enables multiple analyses in a reagentless biosensor scheme.     

Thin Pd membrane on α-Al2O3 hollow fiber substrate without any interlayer by electroless plating combined with embedding Pd catalyst in polymer template

Palladium acetate and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were dissolved in chloroform to form a homogeneous solution. Using this solution, thin polymer template film with embedded Pd catalyst was coated on a porous α-Al₂O₃ hollow fiber substrate. The Pd in the template film was used as the catalyst for electroless plating of Pd membranes. After the template was removed by heat treatment, the thin Pd membranes without any intermediate layers and substrate penetration were synthesized successfully. The as-synthesized Pd composite membranes of thickness less than 5 μm not only have a very high hydrogen permeance/permeability but also have a good hydrogen selectivity. Moreover, the good membrane stability was verified by the long-term operation under the condition of hydrogen permeation and the gas exchange cycles between pure hydrogen and pure helium. The good membrane stability was interpreted by estimating the shear stress of the special membrane configuration with small gap between Pd membrane and porous substrate layer.     

Sieve mechanism estimations for microfiltration membranes with elliptical pores

An established sieve mechanism model for microfiltration was modified to incorporate elliptical pore shapes that arise from uni-axial elongation of track-etch (TE) membranes. The particular membranes investigated were poly(ethylene teraphthalate) TE membranes with an average pore size of 0.6 μm and elongations up to 35.6%. The modified sieve theory predicts that a membrane that has undergone a 35.6% elongation allows for twice the throughput compared to the original membrane with circular pores, while maintaining the same removal ability for a solution containing 1 μm particles.     

Dual electrochemical microsensor for simultaneous measurements of nitric oxide and oxygen: Fabrication and characterization

A planar-type amperometric dual microsensor was developed for the simultaneous measurement of the nitric oxide (NO) and oxygen (O₂) concentrations. The sensor (overall diameter = 500 μm) consisted of a dual working electrode (WE) containing two platinized platinum microdisks (25 μm diameter, WE1, WE2, distance between two disks > 330 μm) and a Ag/AgCl wire reference electrode covered with an expanded poly(tetrafluoroethylene) gas-permeable membrane. The differentiation and concurrent measurements of NO and O₂ were obtained successfully using two sensing WEs with different applied potentials (+0.75 V for WE1 and −0.4 V for WE2). Cross-talk between WE1 and WE2 was eliminated with an optimized internal solution composition. Linear dynamic range, selectivity, sensitivity, detection limit (<5 nM for NO; <500 nM for O₂), and stability (>50 h) were evaluated.     

Amperometric proton selective sensors utilizing ion transfer reactions across a microhole liquid/gel interface

A new cost-effective amperometric proton selective sensor utilizing a single microhole interface between two immiscible electrolyte solutions (ITIES) is developed. The sensing methodology is based on measuring currents associated with proton transfer across the interface assisted by a proton selective ionophore. The ellipse shaped micro-interface was first fabricated by simple mechanical punching with a sharp needle on a thin PVC film (12 μm thick) commercially available as a food wrapping material. The microhole was then filled up with a gellified polyvinylchloride (PVC)-2-nitrophenyloctylether (NPOE) to create a single microhole liquid/liquid interface. Direct ion transfer reactions across the polarized interface serving as ion sensing platforms were studied using cyclic voltammetry. In order to enhance the selectivity of proton sensing, a proton selective ionophore, octadecyl isonicotinate (ETH1778), was incorporated into the organic gel layer and their electrochemical sensing characteristics were investigated using cyclic voltammetry and differential pulse stripping voltammetry. As an example, we employed the proton selective sensor for the determination of glucose concentrations. The detection scheme involves two steps: (i) protons are first generated by the oxidation of glucose with glucose oxidase in the aqueous phase; and (ii) the current associated with the proton transfer across the interface is then measured for correlating the concentration of glucose.     

Ion amperometry at the interface between two immiscible electrolyte solutions in view of realizing the amperometric ion-selective electrode

This article reviews the development in ion amperometry at the interface between two immiscible electrolyte solutions (ITIES) in view of realizing the amperometric ion-selective electrode (ISE). The concept of polarizability of ITIES in a multi-ion system is outlined. Principle aspects of ion amperometry at ITIES are discussed including the use of amperometry as a tool for the clarification of the ion sensing mechanism, and for determining the concentrations of ions in the solution. The reference is made to recent amperometric measurements at the supported liquid membrane (SLM) and polymer composite liquid membranes (PCLM), which, together with the micro-hole supported ITIES, appear to be particularly suitable for realization of the amperometric ISE.     

Conductive diamond hollow fiber membranes

Boron-doped diamond hollow fiber membrane (BDD–HFM) was fabricated as a novel type of porous conductive diamond. BDD–HFM was obtained by deposition of BDD polycrystalline film onto a quartz filter substrate consisting of quartz fibers, followed by etching of the substrate in HF/HNO₃ aqueous solution. Cross-sectional scanning electron microscope (SEM) observation showed the inner diameter and wall thickness of the BDD hollow fibers were in the range of 0.4–2 and 0.2–2 μm, respectively. The BDD–HFM electrode exhibited a relatively large double-layer capacitance (ca. 13 F g⁻¹) in 0.1 M H₂SO₄. Electrochemical AC impedance properties were simulated using an equivalent circuit model containing a transmission line model, which indicated characteristics of a porous electrode material.     

Synthesis and optimization of permselective polymer (polyindoline) film

A polyindoline permselective polymer film was readily synthesized by an electrochemical polymerization of indoline in an aqueous solution of KCl at a potential of 0.4 V vs Ag/AgCl. The amperometric responses of the polyindoline film-coated platinum electrodes to electroactive (ascorbic acid, oxalic acid and hydrogen peroxide) and non-electroactive (lactose, sucrose and urea) substances were measured at a potential of 0.7 V. Effects of various variables such as film thickness, concentrations of monomer and electrolyte, and pH on the permselective behavior of the polymeric membrane were systematically investigated and the optimal values were determined. It was found that permselective polyindoline-coated electrodes prepared in this one-step procedure permitted hydrogen peroxide oxidation while it prevented interference due to oxidizable species such as ascorbic acid and oxalic acid. As a result, it is believed that this polymeric membrane, owing to its permselective character, can be used as the protective material in the construction of hydrogen peroxide-based biosensors. Received: 10 November 1997 / Accepted: 27 January 1998     

Dual quartz crystal microbalance compensation using a submerged reference crystal. Effect of surface roughness and liquid properties

Absolute resonant frequency measurements were made on gold-coated AT-cut quartz crystals with one face in contact with a series of liquids. The effect of surface roughness and liquid properties (viscosity and density) was analyzed in terms of a “trapped liquid” model. In this model, liquid present in surface imperfections is viewed as rigidly coupled mass. In some of the literature this density-dependent, but not viscosity-dependent, term is viewed as being additive to the hydrodynamic shift seen for a smooth surface. Data obtained using 1 μm and 5 μm surface finish crystals are inconsistent with the predictions of the trapped liquid model. This suggests hydrodynamic coupling between liquid internal and external to the crevices. Despite the lack of a theoretical model for the liquid motion, it is possible to compensate for frequency variations resulting from changing liquid properties and for roughness effects by making direct measurements of the resonant frequency difference between two crystals exposed to the same solution. This novel procedure works to the extent that the two crystals have similar surface topographies. Compensation is excellent for 1 μm finish crystals and good for 5 μm finish crystals.     

Comparing flat and micro-patterned surfaces: Gas permeation and tensile stress measurements

Micro-patterning is a suitable method to produce structured membranes that display increased flux compared to flat membranes. In this work we studied the permeation of four different gases (nitrogen, helium, oxygen and carbon dioxide) through Kraton™ polymer (SBS) membranes. It is possible to cast a micro-patterned membrane with 25 μm high and 30 μm wide lines that has a thickness of 5 μm at its thinnest point. Using this micro-pattern, the experimental diffusive gas flux was increased up to 59% compared to non-patterned membranes with the same polymer volume. Finite element simulations confirm this enhancement. Selectivities are similar for both flat and micro-patterned membranes and in accordance with literature. Tensile stress measurements confirm that the micro-patterned membranes yield only limited loss in mechanical strength. Although only one material and geometry is explored here, this principle is generally applicable to all diffusion-driven processes.     

Thermophoretic deposition of palladium aerosol nanoparticles for electroless micropatterning of copper

A method for catalytic activation was introduced by producing palladium aerosol nanoparticles via spark generation and then thermophoretically depositing the particles onto a flexible polyimide substrate through a hole in pattern mask, resulting in a line (24 μm in width) and a square (136 μm × 136 μm) patterns. After annealing, the catalytically activated substrate was placed into a solution for electroless copper deposition. Finally, copper micropatterns of a line (35 μm in width) and a square (165 μm × 165 μm) were formed only on the activated regions of the substrate. Both patterns had the height of 1.6 μm.     

Thick porous tungsten trioxide films by anodization of tungsten in fluoride containing phosphoric acid electrolyte

In the present work, we report on the formation of mesoporous thick tungsten trioxide films grown on tungsten foil by anodization in fluoride containing concentrated phosphoric acid (85%) electrolyte. Under optimized experimental conditions, mesoporous WO₃ films with a thickness up to approximately 2 μm are formed. SEM shows the films to consist of a connected network with a typical pore and feature diameter of ca 50 nm. These films as formed are amorphous and can be annealed to orthorhombic WO₃ structure. These thick porous films can show significant enhanced electrochromic and improved photocatalytic properties.     

一种新型聚合物电解质的研制

合成了聚 (甲基丙烯酸甲酯 丙烯腈 甲基丙烯酸锂 ) (简记为PMAML)新型聚合物电解质基质材料 ,把它与聚偏氟乙烯 (PVDF)共混制备了凝胶化的聚合物电解质 .通过核磁共振波谱确定了PMAML的组份含量 ,并用扫描电镜观察了该聚合物基质膜的表面形貌 .利用交流阻抗技术测试了其电导率 ,室温下电导率可达2 5× 10 - 3S·cm- 1 .采用线性伏安扫描方法研究了该聚合物电解质的电化学稳定性 ,其电化学稳定窗口为4 5V .通过受限扩散实验测得电解质中离子的扩散系数为 8 12× 10 - 7cm2 ·s- 1 .组装的聚合物电解质锂离子电池首次充放电效率为 89% ,前 5次循环容量基本稳定 .     

An improved polymer electrolyte-based amperometric hydrogen sensor

An improved polymer electrolyte membrane (PEM) fuel cell-based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is a PVA/H₃PO₄ blend, which is a proton-conducting solid polymer electrolyte. A thin film of palladium is used as the anode and platinum supported on carbon as the cathode. The sensor functions as a fuel cell, H₂/Pd//PVA-H₃PO₄//Pt/O₂, and the short-circuit current is found to be linearly related to the hydrogen concentration. The basic principle, details of assembly, response behaviour of the sensor and its application are discussed.     

Copolymer electrosynthesis of ethyl-3-thiophene acetate and 3-methylthiophene and characterization of the resulting copolymers by spectroscopic studies

Copolymers of ethyl-3-thiophene acetate (ETA) and 3-methylthiophene (MT) were synthesized electrochemically. Electrospray ionization mass spectra of the electrolyte containing 2×10^–3 M MT + 3×10^–2 M ETA after copolymerization showed cooligomers with different combination of ETA and MT units. Just one value of the glass transition temperature was observed by differential scanning calorimetry of the formation of homogeneous copolymers. Change of the copolymer composition led to change of thermal stability characterized by thermogravimetric analysis. The morphology of the copolymer film was studied by scanning electron microscopy, indicating a homogeneous and compact film. The electroactivity of the homopolymer/copolymer films was studied. Cyclic voltammograms of the polymer films revealed that poly(ethyl-3-thiophene acetate) possesses high electroactivity in non-aqueous solution, but its electroactivity was lost entirely after 50 cycles in 0.1 M N(Bu)₄PF₆/acetonitrile solution having 5 volume percentage of water; however, the copolymer of ETA and MT maintains its high electroactivity even in the aqueous solution. Similar results were also derived from impedance and photoelectrochemical measurements. Additionally, it was found that a bilayer of poly(3-methylthiophene) and copolymer was formed.     

Thick silicate glass film by an interfacial polymerization

A silicate glass film of 2–20 µm in thickness has been formed on a fused quartz substrate by a sol-gel process using an interfacial polymerization technique. A partially hydrolyzed silicon alkoxide was dissolved in hexane and brought into contact with ammonia water in a cylindrical Teflon container. A silica gel film formed at the interface between the two immiscible liquids by the polycondensation of the partially hydrolyzed silicon alkoxide was gently placed on a substrate at the bottom of the container, by draining the liquid. The crack free gel film was dried in an ambient atmosphere and dip-coated with boron ethoxide, followed by sintering in an oven at 1250°C for 1 h. The glass film thus obtained was highly transparent and 2–20 µm in thickness depending on the concentration of the precursor solution and the pH of ammonia water.     

Electrochemical analysis of -penicillamine using a boron-doped diamond thin film electrode applied to flow injection system

The electroanalysis of -penicillamine in 0.1 phosphate buffer (pH 7) was studied at a boron-doped diamond thin film (BDD) electrode using cyclic voltammetry as a function of concentration of analyte and pH of analyte solution. Comparison experiments were performing using a glassy carbon (GC) electrode. The BDD electrode exhibited a well-resolved and irreversible oxidation voltammogram, but the GC electrode provided only an ill-defined response. The BDD electrode provided a linear dynamic range from 0.5 to 10 mM and a detection limit of 25 μM (S/B≥3) in voltammetric measurement. It was also found that the peak potentials were decreased when the pH of the analyte solution was increased. In addition, penicillamine has been studied by hydrodynamic voltammetry and flow injection analysis with amperometric detection using the BDD electrode. The flow injection analysis results at the diamond electrode indicated a linear dynamic range from 0.5 to 50 μM and a detection limit of 10 nM (S/N≈4). The proposed method was applied to determine -penicillamine in dosage form (capsules), the results obtained in the recovery study (255±2.50 mg per tablet) were comparable to those labeled (250 mg per tablet).     

Mesoporous platinum hosts for electrodeliquidliquid – Triple phase boundary redox systems

Mesoporous metal hosts are attractive electrode materials for complex electrode reactions, for example those involving a system of two immiscible liquids. Here we show that a solution of tetraphenylporphyrianto manganese (MnTPP) in 4-(3-phenylpropyl)-pyridine (PPP) organic liquid can be immobilized into mesoporous platinum thin films electrodeposited from a liquid crystalline template. When immersed in an aqueous solution, the organic liquid remains immobilized inside the mesoporous platinum framework. Well-defined, stable, and reproducible ion transfer voltammograms are recorded. The effects of mesoporous platinum membrane thickness (volume), scan rate, and the type of aqueous electrolyte anion (for Cl⁻, , , CN⁻, SCN⁻ and ) are investigated. Mesoporous platinum is proposed as a very effective electrode material for liquidliquid anion sensing and for other applications of electrochemically driven liquidliquid redox systems.     

Modification of carbon ceramic electrode prepared with sol-gel technique by a thin film of chlorogenic acid: application to amperometric detection of NADH

The carbon ceramic electrode prepared with sol-gel technique is modified by a thin film of chlorogenic acid (CGA). By immersing the carbon ceramic electrode in aqueous solution of chlorogenic acid at less than 2 s a thin film of chlorogenic acid adsorbed strongly and irreversibly on the surface of electrode. The cyclic voltammetry of the resulting modified CCE prepared at optimum conditions shows a well-defined stable reversible redox couple due to hydroquinone/quinone system in both acidic and basic solutions. The modified electrode showed excellent electrocatalytic activity toward NADH oxidation and it also showed a high analytical performance for amperometric detection of NADH. The catalytic rate constant of the modified carbon ceramic electrode for the oxidation of NADH is determined by cyclic voltammetry measurement. Under the optimised conditions the calibration curve is linear in the concentration range 1-120 μm. The detection limit (S/N = 3) and sensitivity are 0.2 μM and 25 nA μM⁻¹.The results of six successive measurement-regeneration cycles show relative standard deviations of 2.5% for electrolyte solution containing 1 mM NADH, indicating that the electrode renewal gives a good reproducible and antifouling surface. The advantages of this amperometric detector are: high sensitivity, excellent catalytic activity, short response time t < 2 s, remarkable long-term stability, simplicity of preparation at short time and good reproducibility.     

Controlled production of oil-in-water emulsions containing unrefined pumpkin seed oil using stirred cell membrane emulsification

Membrane emulsification of unrefined pumpkin seed oil was performed using microengineered flat disc membranes on top of which a paddle blade stirrer was operated to induce surface shear. The membranes used were fabricated by galvanic deposition of nickel onto a photolithographic template and contained hexagonal arrays of uniform cylindrical pores with a diameter of 19 or 40 μm and a pore spacing of 140 μm. The uniformly sized pumpkin seed oil drops with span values less than 0.4 were obtained at oil fluxes up to 640 L m⁻² h⁻¹ using 2 wt.% Tween 20 (polyoxyethylene sorbitan monolaurate) or 2–10 wt.% Pluronic F-68 (polyoxyethylene–polyoxypropylen copolymer) as an aqueous surfactant solution. Pumpkin seed oil is rich in surface active ingredients that can be adsorbed on the membrane surface, such as free fatty acids, phospholipids, and chlorophyll. The adsorption of these components on the membrane surface gradually led to membrane wetting by the oil phase and the formation of uniform drops was achieved only for dispersed phase contents less than 10 vol.%. At high oil fluxes, Pluronic F-68 molecules present at a concentration of 2 wt.% could not adsorb fast enough, on the newly formed oil drops, to stabilise the expanding interface.