One-electrode sensors

FfCURE 13.54 Semiconductor gas sensors (o) tubular, (b) thick film, (e) bulk-type one-electrode sensor where a thin Pt wire spiral is embedded Inside a sintered oxide semiconductor button. ... 

On the other hand, electrodes with different geometry were applied to the semiconductor gas sensors. Korotcenkov reviewed practical aspects in the design of one-electrode semiconductor gas sensors. Figure 3.8 shows standard two-electrode and one-electrode sensors schematically in planar view. The schematic electrical circuits of these sensors are also shown in Fig. 3.8, where i pt is a coil resistance of Ft spiral, i Meo is the inter-turn resistance of metal-oxide ceramics and Rs is a total resistance of the sensor. The physical configuration of ceramics type and thin film type one-electrode semiconductor gas sensors are shown in Figs 3.9 and 3.10. ... 

In the one-electrode sensors, the metal resistor simultaneously acts as the heater and the measuring electrode. The operation principle of the one-electrode sensor is based on the shunting of the Pt electrode by the semiconductor oxide, coating the metal spiral or strip. Typically, one-electrode sensors are incorporated in a Wheatstone Bridge circuit, or in the simplest electrical format the change of voltage drop at the sensor is determined. For... 

Golovanov, V., J. L. Solis, V. [.antto, and S. Leppavnori. Different Thick-Film Methods in Prinr-mg ot one-Electrode. Semiconductor Gas Sensors. Sensors Actuators B34 (1996), pp. 410-416. Lantto, V., and V. Golovanov. A Comparison of Conductance Behaviour between SnO> and CdS Gas-Sensitive Films, Sensors Actuators B24-25 (1995), pp. 614-618. 

Several reticulated vitreous carbon (RVC)-plant tissue composite electrodes have also been reported where the open-cell structure of RVC serves as a template for the biocomponent used. One such sensor was constructed by press-fitting 100 pore/in RVC (2-mm thick x 3 or 6 mm OD) cylinders into a 6-mm diameter cavity of a thin-layer cell. The inner side of the disc was pressed into an edge of a copper wire, which provided electrical contact. 

How analytical methods deal with interferences is one of the more ad hoc aspects of method validation. There is a variety of approaches to studying interference, from adding arbitrary amounts of a single interferent in the absence of the analyte to establish the response of the instrument to that species, to multivariate methods in which several interferents are added in a statistical protocol to reveal both main and interaction effects. The first question that needs to be answered is to what extent interferences are expected and how likely they are to affect the measurement. In testing blood for glucose by an enzyme electrode, other electroactive species that may be present are ascorbic acid (vitamin C), uric acid, and paracetamol (if this drug has been taken). However, electroactive metals (e.g., copper and silver) are unlikely to be present in blood in great quantities. Potentiometric membrane electrode sensors (ion selective electrodes), of which the pH electrode is the... 

Oxide Sensors Aluminum oxide can be used as a sensor for moisture analysis. A conductivity call has one electrode node of aluminum,... 

The sensor consisted of a metal cylinder that formed one electrode with a coaxial wire passing down the center that formed the other. A 40 MHz radio frequency was applied across the electrodes and the DC potential that developed across them was fed via simple electronic circuit to a potentiometric recorder. 

Coating the molecular sieve on one electrode of a quartz crystal oscillator is conducted to bricate a gas sensor in this study. The detection performance of the sensors with two different pore sizes of the molecular sieve is examined from their implement in the determination of methanol, ethanol and n-hexane concentration in air. From the performance test, the ruggedness, sensitivity and selectivity of the sensor are investigated. 

A very successful sensor suitable for urea measurement in blood has been developed for Hitachi (Japan) by Tokinaga et al. (1984). Two NH sensitive electrodes containing nonactin in a PVC membrane were integrated in an FIA device in a differential circuit. One electrode was... 

Since not all enzyme-catalyzed reactions involve changes in the level of compounds detectable at an electrode, such as oxygen, or hydrogen peroxide, only a limited number of substances can be determined with one-enzyme sensors. One way of overcoming this problem is to couple the catalytic activities of different enzymes either in sequence, in competing pathways, or in cycles. In general, enzymes to be used in multienzyme electrodes should fulfil the following requirements ... 

The device is manufactured by laminating three different functional films (1) a base plastic film with organic transistors (2) a pressure-sensitive rubber sheet and (3) a film suspending copper electrodes for power supply. One sensor cell (sensei) consists of one organic transistor and one pressure sensor. 

Preliminary results are presented for the use of cyclic voltammetiy as a method for pattern recognition. The current at eight potentials of a cyclic voltammgramm was analyzed and these values served as a simulation of eight amperometric sensors. It is shown that on the basis of this procedure, different explosives and apple juices are easily distinguished by the use of one electrode alone These results clearly show that cyclic voltammetry could easily be used for a so called electronic tongue. In the future it is planned to use cyclic voltammetry as a method in combination with different sensor methods and also for the vapour detection. 

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