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Sensors, Volume 3, Issue 7 (July 2003), Pages 202-275

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Research

Open AccessArticle Flow-velocity Microsensors Based on Semiconductor Fieldeffect Structures
Sensors 2003, 3(7), 202-212; doi:10.3390/s30700202
Received: 18 May 2003 / Accepted: 24 June 2003 / Published: 27 July 2003
Cited by 5 | PDF Full-text (913 KB) | HTML Full-text | XML Full-text
Abstract
A time-of-flight-type flow-velocity sensor employing the in-situ electrochemically generation of ion-tracers is developed. The sensor consists of an ion generator and two downstream-placed pH-sensitive Ta2O5-gate ISFETs (ion-sensitive field-effect transistor) that detect generated H+- or OH--ions. The results of the
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A time-of-flight-type flow-velocity sensor employing the in-situ electrochemically generation of ion-tracers is developed. The sensor consists of an ion generator and two downstream-placed pH-sensitive Ta2O5-gate ISFETs (ion-sensitive field-effect transistor) that detect generated H+- or OH--ions. The results of the developed flow-velocity sensor under different modes of ion generation are presented and discussed. By applying this ISFET-array, the time of flight, and consequently, the flow velocity can be accurately evaluated using the shift of the response curve of the respective ISFETs in the array along the time scale. A good linearity between the measured flow velocity with the ISFET-array and the delivered flow rate of the pump is observed. In addition, a possibility of flowvelocity measurements by means of a LAPS (light-addressable potentiometric sensor) is firstly demonstrated. Full article
Open AccessArticle A poly(pyrrole-Cobalt(II)deuteroporphyrin) electrode for the potentiometric determination of nitrite
Sensors 2003, 3(7), 213-222; doi:10.3390/s30700213
Received: 8 April 2003 / Accepted: 11 June 2003 / Published: 27 July 2003
Cited by 16 | PDF Full-text (173 KB)
Abstract
The electrochemical properties of a new Co(II) deuteroporphyrin substituted by two electropolymerizable pyrrole groups has been investigated in organic solvent. This functionalization has allowed the preparation of the first example of a cobalt deuteroporphyrin film by oxidative electropolymerization. The resulting conducting polypyrrole film
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The electrochemical properties of a new Co(II) deuteroporphyrin substituted by two electropolymerizable pyrrole groups has been investigated in organic solvent. This functionalization has allowed the preparation of the first example of a cobalt deuteroporphyrin film by oxidative electropolymerization. The resulting conducting polypyrrole film exhibits the regular electroactivity of cobalt deuteroporphyrin. Compared to conventional cobalt porphyrin electrochemistry, the replacement of porphyrin macrocycle by deuteroporphyrin ring results in markedly more negative potential values for the metalcentered oxidation and reduction processes. The influence of NO2- as axial ligand on the reductive behavior of the electropolymerized cobalt (II) deuteroporphyrin is examined. The recognition properties of the film illustrated by the potentiometric shift of the Co(II)/(I) reduction were exploited for the determination of NO2- in the concentration range 2 10-6- 2.5 10-4 M. Full article
Open AccessArticle A Porphyrin Based Potentiometric Sensor for Zn2+ Determination
Sensors 2003, 3(7), 223-235; doi:10.3390/s30700223
Received: 29 June 2003 / Accepted: 15 July 2003 / Published: 27 July 2003
Cited by 25 | PDF Full-text (911 KB)
Abstract
PVC based membranes of disodium salt of porphyrin 3,7,12,17-tetramethyl-8, 13-divinyl 2,18-porphine dipropionic acid (I) as ionophore with sodium tetra phenyl borate (NaTPB) as anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutyl butyl phosphonate (DBBP), tris(2- ethyl hexyl)phosphate (TEP), tri-n-butylphosphate (TBP) and
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PVC based membranes of disodium salt of porphyrin 3,7,12,17-tetramethyl-8, 13-divinyl 2,18-porphine dipropionic acid (I) as ionophore with sodium tetra phenyl borate (NaTPB) as anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutyl butyl phosphonate (DBBP), tris(2- ethyl hexyl)phosphate (TEP), tri-n-butylphosphate (TBP) and 1- chloronaphthalene (CN) as plasticizing solvent mediators were prepared and constructed for determination of Zn(II). The PVC based membrane of (I) with DBBP as plasticizer and having anion excluder, NaTPB in the ratio PVC: I: NaTPB: DBBP (150: 10: 2: 200) gave the best results in terms of working concentration range (1.3×10-5-1.0 ×10-1M) with a Nernstian slope (30.0 mV/decade of activity). The useful pH range of the sensor is 3.0 –7.4, beyond which a drift in potential was observed. The response time of the sensor is 10s and the lifetime was about 2 months during which it could be used without any measurable divergence. It had good stability and reproducibility. The membrane worked satisfactorily in non-aqueous medium up to 40% (v/v) non-aqueous content. The selectivity coefficient values indicate that the electrode is highly selective for Zn2+ over a number of other cations except Na+ and Cd2+. Although Na+ and Cd2+ are likely to cause some interference, they would not interfere if present at the concentrations < 1 ×10-5 and < 5 ×10-5 M, respectively. The electrode has been used as an indicator electrode to determine the end point in the potentiometric titration of Zn2+ with EDTA. Full article
Open AccessArticle Development of a Surface Acoustic Wave Sensor for In-Situ Monitoring of Volatile Organic Compounds
Sensors 2003, 3(7), 236-247; doi:10.3390/s30700236
Received: 24 June 2003 / Accepted: 11 July 2003 / Published: 27 July 2003
Cited by 39 | PDF Full-text (575 KB)
Abstract
This paper describes the development of a surface-acoustic-wave (SAW) sensor that is designed to be operated continuously and in situ to detect volatile organic compounds. A ruggedized stainless-steel package that encases the SAW device and integrated circuit board allows the sensor to be
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This paper describes the development of a surface-acoustic-wave (SAW) sensor that is designed to be operated continuously and in situ to detect volatile organic compounds. A ruggedized stainless-steel package that encases the SAW device and integrated circuit board allows the sensor to be deployed in a variety of media including air, soil, and even water. Polymers were optimized and chosen based on their response to chlorinated aliphatic hydrocarbons (e.g., trichloroethylene), which are common groundwater contaminants. Initial testing indicates that a running-average data-logging algorithm can reduce the noise and increase the sensitivity of the in-situ sensor. Full article
Open AccessArticle The Influence of the Enzyme Membrane Thickness on the Response of Amperometric Biosensors
Sensors 2003, 3(7), 248-262; doi:10.3390/s30700248
Received: 22 May 2003 / Accepted: 10 July 2003 / Published: 27 July 2003
Cited by 31 | PDF Full-text (344 KB) | HTML Full-text | XML Full-text
Abstract
A mathematical model of amperometric biosensors has been developed. The model is based on non-stationary diffusion equations containing a non-linear term related to Michaelis-Menten kinetics of the enzymatic reaction. Using digital simulation, the influence of the thickness of enzyme membrane on the biosensor
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A mathematical model of amperometric biosensors has been developed. The model is based on non-stationary diffusion equations containing a non-linear term related to Michaelis-Menten kinetics of the enzymatic reaction. Using digital simulation, the influence of the thickness of enzyme membrane on the biosensor response was investigated. The digital simulation of the biosensor operation showed the non-monotonous change of the maximal biosensor current versus the membrane thickness at the various maximal enzymatic rates. Digital simulation was carried out using the finite difference technique. Results of the numerical simulation was compared with known analytical solutions. This paper presents a framework for selection of the membrane thickness, ensuring the sufficiently stable sensitivity of a biosensor in a required range of the maximal enzymatic rate. Full article
Open AccessArticle Experimental Determination of Bending Resonances of Millimeter Size PVF2 Cantilevers
Sensors 2003, 3(7), 263-275; doi:10.3390/s30700263
Received: 20 May 2003 / Accepted: 6 July 2003 / Published: 27 July 2003
Cited by 1 | PDF Full-text (360 KB)
Abstract
The polymer piezoelectric polvinylidene fluoride has found widespread use in sensors and actuators. The bending mode of piezoelectricity offers very high sensitivities and low mechanical input impedance, but has not been studied in as much detail for sensor applications. We report the dynamic
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The polymer piezoelectric polvinylidene fluoride has found widespread use in sensors and actuators. The bending mode of piezoelectricity offers very high sensitivities and low mechanical input impedance, but has not been studied in as much detail for sensor applications. We report the dynamic electromechanical properties of millimeter size cantilevers made from electroded films of PVF2. All devices tested had a single polymer layer. Several resonances are found below 1 kHz and the experimentally observed resonance frequency dependence on cantilever thickness and length are seen to agree well with published models which take the properties of the electrodes into account. It is found that bending resonances are also modulated by the width of the cantilever. Therefore, though the length and thickness control the resonance frequency most strongly, the actual realized value can be fine-tuned by changing cantilever width and the electrode material and its thickness. Further, all resonances display high piezoelectric coupling coefficients (keff), ranging between 0.2 - 0.35. The data presented here will be extremely useful in the design of sensors and actuators for a number of applications, since the combination of millimeter size scales and high piezoelectric sensitivities in the low audio range can be realized with this marriage of polymeric materials and cantilever geometries. Such an array of sensors can be used in cochlear implant applications, and when integrated with a resonance interrogation circuit can be used for the detection of low frequency vibrations of large structures. If appropriate mass/elasticity sensitive layers are coated on the electrodes, such a sensor can be used for the detection of a wide range of chemicals and biochemicals. Full article

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