ISFETs with sputtered sodium alumino-silicate glass membranes

Sodium ion sensitive field-effect transistors (ISFETs) based on reactively sputtered sodium aluminosilicate (NAS) glass membranes are investigated. Using an inverted cylindrical magnetron, NAS films with defined and reproducible composition are obtained. Radiation damage in the gate dielectric is largely eliminated by annealing at 450°C. The Na⁺ sensitivity, the selectivity with respect to H⁺ and K⁺ ions, the response time, the conditioning period, the long-term drift, and the lifetime are evaluated. The ISFETs exhibit a near-Nernstian Na⁺ response down to 10^-4 mol/l in solutions of pH7. The NAS films are physically very robust and have excellent chemical durability, e.g., a sensor with a 110 nm thick membrane lasts for about 8 months. The overall sensor properties compare well with those of a commercial Na⁺ selective glass electrode.     

Potentiometric determination of d(+)glucose, d(+)mannose or d(-)fructose in a mixture of hexoses and pentoses, by using streptococcus mutans fermentation

A potentiometric sensor has been developed, based on selective fermentation of carbohydrates by Streptococcus mutans. This combination of bacterial action and a glass electrode responds to beta-d(+)glucose, d(+)mannose and beta-d(-)fructose over a narrow concentration range, with a response time of 4 min, and has negligible response to other hexoses and pentoses.     

Nitrate ion-sensitive field effect transistor based on bis(bathocuproin)-copper(I) nitrate dissolved in solid solvents

Nitrate-selective ion-sensitive field effect transistors (ISFETs) were prepared by dip-coating the silica gate insulator surface with an ion exchanger based on bis(bathocuproin)-copper(I) nitrate in a molten mixture of docosan 1-ol and Triphenylphosphate. This sensor showed a linear response from 10⁻¹ mol dm⁻³ to at least 10⁻⁵ mol dm⁻³ and maintained its response characteristics for as long as 5 weeks. The selectivity sequence for common anions such as Cl0−₄ and Cl− followed the conventional Hofmeister series. This sensor was applied to rain water analysis.     

A novel potassium ion membrane sensor based on rifamycin neutral ionophore

A novel potentiometric membrane sensor for potassium ion based on the use of rifamycin as a neutral ionophore is described. The sensing membrane is formulated with 2 wt.% rifamycin-SV, 69 wt.% dibutylsebacate plasticizer and 29 wt.% PVC. Linear and stable potential response with near-Nernstian slope of 56.7 +/- 0.2 mV decade(-1) are obtained over the concentration range 1 x 10(-1)-3 x 10(-5) M K(+). The detection limit is 0.3 microg ml(-1) K(+), the response time is 10-30 s and the working pH range is 4-11. Responses of the sensor toward alkali and alkaline earth metal ions are in the order K(+) > Rb(+) > Cs(+) > Na(+) > NH(4)(+) > Ba(2+) > Mg(2+) > Ca(2+) > Sr(2+) > Li(+). The selectivity coefficient data reveal negligible interference from transition metal ions. Direct potentiometric determination of K(+) in the presence of 10-50-fold excess of alkali and alkaline earth metals gives results with an average recovery of 99.1%, and a mean standard deviation of 1.2%. The data agree fairly well with those obtained by flame photometry.     

聚苯胺修饰碳纤维超微pH传感器研究及其在植物柱头活体测试中的应用

作为探测生命奥秘的重要手段,微电极技术已广泛应用于活体分析[1－3]．传统的pH玻璃电极难以实现活体微区或微环境分析,因此,研制微型和超微型pH传感器意义重大．本文采用电化学聚合法将聚苯胺修饰在碳纤维微柱电极上,制成对pH具有能斯特响应的超微型pH传感器,与pH玻璃电极比较,发现它具有响应快、稳定性高、重现性好及选择性高等特点．用该超微pH传感器首次实现了对答苔属植物活体柱头乳突细胞和花粉粒表面微环境的pH值测定．为生物学家深入研究花粉萌发的生理过程和机理提供了十分有用的信息．1实验部分1．1仪器和试剂M366双恒…     

Determination of d(+)glucose, d(+)mannose, d(+)galactose or d(-)fructose in a mixture of hexoses and pentoses by use of dental plaque coupled with a glass electrode

A potentiometric sensor has been developed by coupling dental plaque with a flat-surface glass electrode. Selectivity of this electrode for hexoses and pentoses has been tested. The electrode responds linearly to beta-d(+)glucose, d(+)mannose, d(+)galactose and beta-d(-)fructose over a narrow concentration range between 10(-4) and 10(-3)M, but has negligible response to the other hexoses and pentoses. This "plaque" electrode, using live bacterial cells, may serve as a model for the development of other selective electrodes for carbohydrates.     

Recent trends in potentiometric sensor arrays--a review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.     

Simple PVC–PPy electrode for pH measurement and titrations

Cobaltabis(dicarbollide) [3,3'-Co(1,2-C2B9H11)](-)-doped polypyrrole (PPy) films have been prepared galvanostatically on glassy carbon electrodes in acetonitrile solution. The potential response behavior of the film of this new material has been investigated in some common pH buffers and in acid-base titrations. The potentiometric characteristics of the resulting films are indicative of a quasi-Nernstian response (approximately 50 mV/pH unit), a linearity range from pH 12 to 3 and correlation coefficients (r2) of approximately 0.98. The electrode is suitable for pH measurements and for monoprotic titrations of strong alkalis with strong acids, and weak bases with strong acids, but the long response time hinders the use of this electrode for multiprotic titrations. The time response has been dramatically improved by reducing the film thickness by using the template effect of a non-conducting polymer (PVC) cast over the graphite surface before PPy deposition. PPy polymerization occurs in the free channels of PVC leading to the formation of PPy wires. The morphological change of PPy does not affect the slope or linearity range. The response of the PVC-PPy electrochemical sensor is rapid and the sensor is easy to prepare, at low cost, and its performance is comparable with that of commercial glass electrodes.     

New solid-state ion-selective electrodes — Sensors for chemical analysis of solutions

Summary From the historic point of view one can consider chalcogenide glass ion-selective electrodes (CGISEs) and ion-selective field effect transistors (ISFETs) as new solid-state sensors for chemical analysis. The paper describes the development of the sensors, the methods of investigation, analytical properties and the sensing mechanism of CGISEs and ISFETs.

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Neue ionen-selektive Festkörperelektroden — Sensoren für die chemische Analyse von Lösungen

     

Evaluation of co-polyaniline nanocomposite thin films as humidity sensor

Spin coated films of Co-Polyaniline nanocomposite are evaluated for their transmission properties using He-Ne laser for humidity sensing. The thickness (17-29 microm) of the films is varied by multiple deposition of Co-Polyaniline nanocomposite on a glass substrate. The samples exhibit typically two to three regions in their sensitivity curve when tested in the relative humidity (RH) range of 20-95%. The sensitivity ranges from 0.1 mV/%RH to 12.26 mV/%RH for lower to higher thickness. The sensors show quick response of 8s (20-95%RH), and a recovery time of 1 min (95-20%RH) with good repeatability, reproducibility and low hysteresis effect. The sensitivity of the sensor increases with humidity and thickness. Material characterization is done by X-ray diffraction (XRD), scanning electron micrograph (SEM) and Fourier transform infra-red spectroscopy (FTIR).     

Synthesis of polypyrrole films for the development of ammonia sensor

In the present investigation, we have synthesized a polypyrrole films by chemical polymerization technique for the development of ammonia sensor. The polypyrrole films were synthesized in an aqueous acidic medium on glass substrate with mild oxidation of ferric chloride at temperature 29°C. The concentrations (molar) of monomer (pyrrole), oxidant (ferric chloride), and dopant (polyvinyl sulfonate) have been optimized for the uniform and porous surface morphology of the synthesized polypyrrole film. The synthesized films were characterized by scanning electron microscopy, ultraviolet‐visible, and Fourier transforms infrared spectroscopy. Ammonia gas sensing behavior of polypyrrole films was studied by using indigenously developed gas sensing chamber. The synthesized polypyrrole film with optimized process parameters shows excellent and reproducible response to low concentration (100 ppm) of ammonia gas. Copyright © 2007 John Wiley & Sons, Ltd.     

Creatinine sensitive biosensor based on ISFETs and creatinine deiminase immobilised in BSA membrane

A creatinine sensitive biosensor based on ion sensitive field-effect transistors (ISFETs) with immobilised creatinine deiminase (CD) is developed. CD is immobilised on the transducer surface by classical cross-linking with bovine serum albumin (BSA) in a glutaraldehyde (GA) vapour. The linear dynamic ranges of biosensors are between 0 and 5 mM creatinine concentration, and the sensor sensitivity depends on the sample buffer concentration. Minimal detection limit for creatinine determination in model solution with 144 mM NaCl and 5% BSA, pH 7.4, is about 10 muM. Biosensor responses are reproducible and stable during continuous work at least for 8 h, and the relative standard deviation of sensor response is approximately 3% (n=48, for creatinine concentrations of 0.2 and 0.6 mM). An investigation about storage stability of creatinine sensitive ENFETs kept in dry at 4-6 degrees C shows that biosensors demonstrate an excellent storage stability for at least 6 months and more. Moreover, creatinine sensitive enzymatic field-effect transistors (ENFETs), demonstrating very good performances, are very selective and specific and well suitable for hemodialysis monitoring.     

氧化锌薄膜/锡掺杂玻璃光波导元件及其对氯苯的气敏性研究

建立了玻璃光波导气敏元件检测氯苯气体的方法.采用浸渍-提拉法将ZnO敏感膜固定在锡掺杂玻璃光波导表面,研制出了检测氯苯气体的ZnO薄膜/锡掺杂玻璃光波导气敏元件,并用该玻璃光波导气敏元件对挥发性有机气体进行了检测.实验结果表明,在室温下,气敏元件对氯苯气体有明显的响应,而对相同浓度的其它挥发性有机气体的响应相对较小,对...     

The ionic product of water in highly concentrated sodium perchlorate solutions

The ionic product of water, pK(w)=-log[H(+)][OH(-)], has been determined in aqueous solutions of sodium perchlorate over the concentration range of 1.0-8.0 M at 25 degrees C from high-precision potentiometric titrations carried out in cells with liquid junction using both glass and hydrogen electrodes. The glass electrode results are systematically lower probably as a result of interference by Na(+) ions.     

Protolytic behavior of hydroxylated Pyrex glass surfaces in NaCl media

Adsorption of hydrogen ions from aqueous NaCl solutions at the Pyrex glass-water interface was investigated by acid-base titration (glass electrode) at 25 degrees C and at the ionic strengths 0.010, 0.030, 0.10, 1.0, and 3.0 mol dm(-3). The pH values ranged from 2 to 7. The Pyrex samples had a specific surface area of 19.2x10(3) m(2)kg(-1) and a porous structure (pores 2.4 nm thick, 280 nm long). The reactions were found to be extremely slow but showed good reversibility. The potentiometric data, due to the small effect of ionic strength on the equilibria, were fitted with a simple nonelectrostatic model based on strong specific interactions of medium ions with deprotonated silanol, >SiO(-), and boranol, >BO(-), as well as with protonated sites. The acid-base properties are described by the reactions and equilibrium constants at the infinite dilution reference state: >SiONa + H(+) <==> >SiOHNa(+), logbeta110Si=3.1+/-0.2; >SiONa + 2H(+) + Cl(-) <==> >SiOH(2)Cl + Na(+), logbeta201Si=6.75+/-0.15; >SiONa + H(+) <==> >SiOH + Na(+), logbeta100Si=1.8+/-0.2, >BONa + H(+) <==>BOH + Na(+), logbeta100B=6.4+/-0.2; >BONa + H(+) <==> >BOHNa(+), logbeta110B=6.6+/-0.2; >BONa + 2H(+) <==> >BOH(+)(2) + Na(+), logbeta200B=11.56+/-0.15.     

Photocurable ISFET for anionic surfactants. Monitoring of photodegradation processes

The preparation of a new ion-selective field-effect transistor (ISFET) based on a photocurable membrane sensitive to anionic surfactants is described. The membrane is formed by an urethane-acrylate matrix with 2-cyanophenyl octyl ether as the plasticiser. When compared to conventional ion-selective electrodes, the prepared ISFETs do not show significant differences in sensitivity and reproducibility (P=0.05). When calibrating with dodecylbenzenesulfonate (DBS(-)) the prepared ISFETs show a nernstian behaviour, with a slope of 57.5 mV per decade. The linear working range is 1.0x10(-3) to 3.0x10(-6) M DBS(-) and the detection limit is 1.2x10(-6) M. The response times were below 0.7 min in all cases (95% of the step change). As the application, photodegradation processes using titanium dioxide dispersions, were monitored for two common anionic surfactants: DBS(-), being aromatic, and the more alkylic dodecylsulfate, DS(-). The determination of surfactant concentration was performed following a standard addition methodology, using ISFETs as the sensors, and without any previous separation stages. The degradation kinetics in both cases are first-order processes, with half-life times (t(0.5)) of 31.5 min for DBS(-) and 52.0 min for DS(-).     

Investigation of relative humidity effects on the response behavior of a pH indicator-based OWG vapor sensor

The response of a pH indicator-based optical waveguide sensor was characterized with respect to the effects of relative humidity (RH) on the magnitude of the sensor response, and on the rate of response to both hydrochloric acid and ammonia/ammonium hydroxide vapors. Water vapor constitutes both a chemical and a systematic (optical) interference for the OWG sensor response to hydrochloric acid. Swelling of the polymer films upon exposure to water vapor results in a decrease in the loss of light at the polymer/air interface, resulting in an increase in the sensor signal. In addition, high RH conditions decrease the bromothymol blue indicator response to hydrochloric acid vapor. In contrast, the bromothymol blue indicator response to ammonia increases as the RH increases. High RH levels also increases the rate of diffusion (transport) of hydrochloric acid into (and out of) Nafion films, but does not affect the diffusion rate for poly(vinyl alcohol) polymer films. The RH does not appear to have any significant effect on the rate of transport of ammonia in any of the polymer films studied.     

Silicon nanowire ion sensitive field effect transistor with integrated Ag/AgCl electrode: pH sensing and noise characteristics

We have fabricated Si nanowire (SiNW) based ion-sensitive field effect transistors (ISFETs) for biosensing applications. The ability to prepare a large number of sensors on a wafer, the use of standard silicon microfabrication techniques resulting in cost savings, and potential high sensitivity are significant advantages in favor of nanoscale SiNW ISFETs. The SiNW ISFETs with embedded Ag/AgCl reference electrode were fabricated on a standard silicon-on-insulator wafer using electron-beam lithography and conventional semiconductor processing technology. The current-voltage characteristics show an n-type FET behavior with a relatively high on/off current ratio, reasonable sub-threshold swing value, and low gate-leakage current. The pH responses of the ISFETs with different pH solutions were characterized at room temperature which showed a clear lateral shift of the drain current vs. gate voltage curve with a change in the pH value of the solution and a sensitivity of 40 mV pH(-1). The low frequency noise characteristics were investigated to evaluate the signal to noise ratio and sensing limit of the devices.     

Redox-active ionic-liquid-assisted one-step general method for preparing gold nanoparticle thin films: applications in refractive index sensing and catalysis

We describe a general one-step facile method for depositing gold nanoparticle (GNP) thin films onto any type of substrates by the in situ reduction of AuCl(3) using a newly designed redox-active ionic liquid (IL), tetrabutylphosphonium citrate ([TBP][Ci]). Various substrates such as positively charged glass, negatively charged glass/quartz, neutral hydrophobic glass, polypropylene, polystyrene, plain paper, and cellophane paper are successfully coated with a thin film of GNPs. This IL ([TBP][Ci]) is prepared by the simple neutralization of tetrabutylphosphonium hydroxide with citric acid. We also demonstrate that the [TBP][Ci] ionic liquid can be successfully used to generate GNPs in an aqueous colloidal suspension in situ. The deposited GNP thin films on various surfaces are made up of mostly discrete spherical GNPs that are well distributed throughout the film, as confirmed by field-emission scanning electron microscopy. However, it seems that some GNPs are arranged to form arrays depending on the nature of surface. We also characterize these GNP thin films via UV-vis spectroscopy and X-ray diffractometry. The as-formed GNP thin films show excellent stability toward solvent washing. We demonstrate that the thin film of GNPs on a glass/quartz surface can be successfully used as a refractive index (RI) sensor for different polar and nonpolar organic solvents. The as-formed GNP thin films on different surfaces show excellent catalytic activity in the borohydride reduction of p-nitrophenol.     

Optical Sol-Gel-Based Dissolved Oxygen Sensor: Progress Towards a Commercial Instrument

A dissolved oxygen sensor based on fluorescence quenching of the oxygen-sensitive ruthenium complex, [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline]2+, which has been immobilized in a porous silica sol-gel-derived film, is reported. Ormosil sensing films were fabricated using modified silica precursors such as methyltriethoxysilane (MTEOS) and ethyltriethoxysilane (ETEOS) and were dip-coated onto planar glass substrates. Tailoring of the films for dissolved oxygen (DO) sensing is described whereby sensor response is optimized by maximizing film hydrophobicity by the use of the modified precursors. Sensor performance parameters such as limit of detection and sensor resolution are reported. Issues such as dye leaching and photobleaching are discussed. Progress towards a commercial instrument is reported.