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179 KiB

Open AccessArticle

Mediated Electron Transfer at Redox Active Monolayers Part 2 : Analysis of the Chronoamperometric Response to a Potential Step Perturbation

by Michael E.G. Lyons

Sensors 2002, 2(8), 314-330; https://doi.org/10.3390/s20800314 - 17 Aug 2002

Cited by 14 | Viewed by 6738

Abstract

A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. We describe theoretically the time dependent chronoamperometric response expected for a redox active monolayer in [...] Read more.

A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. We describe theoretically the time dependent chronoamperometric response expected for a redox active monolayer in the absence of a substrate in solution, and subsequently extend the analysis to consider the reaction of a solution phase substrate mediated by surface immobilized redox groups. This is accomplished via a Laplace transform based solution of the Fick diffusion equation for the substrate transport to the monolayer surface coupled with the development of a suitable flux matching condition at the monolayer/solution interface . The latter procedure enables the development of an analytical expression for the transient current response in terms of well established mathematical special functions. We have shown that kinetic information may be readily extracted from the developed expressions for the current response as a function of time. In the present paper we assume that the reaction between mediator and substrate is of a simple outer sphere bimolecular type. Full article

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608 KiB

Open AccessArticle

Ethylene Detection Using Nanoporous PtTiO₂ Coatings Applied to Magnetoelastic Thick Films

by Rhong Zhang, M. I. Tejedor, Marc A. Anderson, Maggie Paulose and Craig A. Grimes

Sensors 2002, 2(8), 331-338; https://doi.org/10.3390/s20800331 - 22 Aug 2002

Cited by 31 | Viewed by 8561

Abstract

This paper reports on the use of nanoporous Pt-TiO₂ thin films coated onto magnetoelastic sensors for the detection of ethylene, an important plant growth hormone. Five different metal oxide coatings, TiO₂, TiO₂+ZrO₂, TiO₂+TTCN(1,4,7-Trithiacyclononane)+Ag, SiO [...] Read more.

This paper reports on the use of nanoporous Pt-TiO₂ thin films coated onto magnetoelastic sensors for the detection of ethylene, an important plant growth hormone. Five different metal oxide coatings, TiO₂, TiO₂+ZrO₂, TiO₂+TTCN(1,4,7-Trithiacyclononane)+Ag, SiO₂+Fe, and TiO₂+Pt, each having demonstrated photocatalytic activity in response to ethylene, were investigated for their ability to change mass or elasticity in response to changing ethylene concentration. Pt-TiO₂ films were found to possess the highest sensitivities, and coupled with the magnetoelastic sensor platform capable of sensing ethylene levels of < 1 ppm. Full article

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69 KiB

Open AccessArticle

A Hydrogen Ion-Selective Sensor Based on Non-Plasticised Methacrylic-acrylic Membranes

by Lee V Heng, Loh Han Chern and Musa Ahmad

Sensors 2002, 2(8), 339-346; https://doi.org/10.3390/s20800339 - 22 Aug 2002

Cited by 15 | Viewed by 8681

Abstract

A methacrylic-acrylic polymer was synthesised for use as a non-plasticised membrane for hydrogen ion-selective sensor incorporating tridodecylamine as an ionophore. The copolymer consisted of methyl methacrylate and n-butyl acrylate monomers in a ratio of 2:8. Characterisation of the copolymer using FTNMR demonstrated that [...] Read more.

A methacrylic-acrylic polymer was synthesised for use as a non-plasticised membrane for hydrogen ion-selective sensor incorporating tridodecylamine as an ionophore. The copolymer consisted of methyl methacrylate and n-butyl acrylate monomers in a ratio of 2:8. Characterisation of the copolymer using FTNMR demonstrated that the amount of each monomer incorporated during solution polymerisation was found to be similar to the amount used in the feed before polymerisation. The glass transition temperature of the copolymer determined by differential scanning calorimetry was -30.9 ºC. Potentiometric measurements conducted showed a linear pH response range of 4.3 – 9.6 with the response slope of 56.7 mV/decade. The selectivity of the sensors towards hydrogen ions was similar to other plasticiser based membrane electrodes and the logarithmic selectivity coefficients for discrimination against interference cations is close to –9.7. However, the incorporation of a lipophilic anion as membrane additive is essential in ensuring optimum performance of the hydrogen ion sensor. Full article

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92 KiB

Open AccessArticle

Gamma Radiation Dosimetry Using Tellurium Dioxide Thin Film Structures

by Khalil Arshak and Olga Korostynska

Sensors 2002, 2(8), 347-355; https://doi.org/10.3390/s20800347 - 23 Aug 2002

Cited by 69 | Viewed by 9310

Abstract

Thin films of Tellurium dioxide (TeO2) were investigated for γ-radiation dosimetry purposes. Samples were fabricated using thin film vapour deposition technique. Thin films of TeO2 were exposed to a 60Co γ-radiation source at a dose rate of 6 Gy/min at room temperature. Absorption [...] Read more.

Thin films of Tellurium dioxide (TeO2) were investigated for γ-radiation dosimetry purposes. Samples were fabricated using thin film vapour deposition technique. Thin films of TeO2 were exposed to a 60Co γ-radiation source at a dose rate of 6 Gy/min at room temperature. Absorption spectra for TeO2 films were recorded and the values of the optical band gap and energies of the localized states for as-deposited and γ-irradiated samples were calculated. It was found that the optical band gap values were decreased as the radiation dose was increased. Samples with electrical contacts having a planar structure showed a linear increase in current values with the increase in radiation dose up to a certain dose level. The observed changes in both the optical and the electrical properties suggest that TeO2 thin film may be considered as an effective material for room temperature real time γ-radiation dosimetry. Full article

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Sensors, Volume 2, Issue 8 (August 2002) – 4 articles , Pages 314-355

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