Electrochemical sensor types

Enzyme Immunosensors. Enzyme immunosensors are enzyme immunoassays coupled with electrochemical sensors. These sensors (qv) require multiple steps for analyte determination, and either sandwich assays or competitive binding assays maybe used. Both of these assays use antibodies for the analyte of interest attached to a membrane on the surface of an electrochemical sensor. In the sandwich assay type, the membrane-bound antibody binds the sample antigen, which in turn binds another antibody that is enzyme-labeled. This immunosensor is then placed in a solution containing the substrate for the labeling enzyme and the rate of product formation is measured electrochemically. The rate of the reaction is proportional to the amount of bound enzyme and thus to the amount of the analyte antigen. The sandwich assay can be used only with antigens capable of binding two different antibodies simultaneously (53). 

Nowadays all over the world considerable attention is focused on development of chemical sensors for the detection of various organic compounds in solutions and gas phase. One of the possible sensor types for organic compounds in solutions detection is optochemotronic sensor - device of liquid-phase optoelectronics that utilize effect of electrogenerated chemiluminescence. In order to enhance selectivity and broaden the range of detected substances the modification of working electrode of optochemotronic cell with organic films is used. Composition and deposition technique of modifying films considerably influence on electrochemical and physical processes in the sensor. 

Microfabrication technology has made a considerable impact on the miniaturization of electrochemical sensors and systems. Such technology allows replacement of traditional bulky electrodes and beaker-type cells with mass-producible, easy-to-use sensor strips. These strips can be considered as disposable electrochemical cells onto which the sample droplet is placed. The development of microfabricated electrochemical systems has the potential to revolutionize the field of electroanaly-tical chemistry. 

In addition to chromatography based on adsorption, ion pair chromatography (IP-HPLC) and capillary electrophoresis (CE) or capillary zone electrophoresis (CZE) are new methods that became popular and are sufficiently accurate for these types of investigations. Other methods involving electrochemical responses include differential pulse polarography, adsorptive and derived voltammetry, and more recently, electrochemical sensors. 

A rational manipulation of the electrode surface functionality by immobilizing selected types of molecules is an essential key for the development of electrochemical sensors and devices. One of the recent studies in this area has focused on monolayer formation on gold surfaces from organosulfur precursors [11]. Stable attachment of organic molecules to gold... 

The goal of this book is to cover the full scope of electrochemical sensors and biosensors. It offers a survey of the principles, design and biomedical applications of the most popular types of electrochemical devices in use today. The book is aimed at all scientists and engineers who are interested in developing and using chemical sensors and biosensors. By discussing recent advances, it is hoped to bridge the common gap between research literature and standard textbooks. 

One interesting development in the carbon nanotube-based electrochemical sensor is the ability to self-assemble the CNT to other types of nano materials such as gold and silver nanoparticles or to a polymer surface. The enhancement of Raman signals of carbon nanotubes through the adsorption on gold or silver substrate has been also reported [142-146],... 

In the early part of this century, many types of solid electrolyte had already been reported. High conductivity was found in a number of metal halides. One of the first applications of solid electrolytes was to measure the thermodynamic properties of solid compounds at high temperatures. Katayama (1908) and Kiukkola and Wagner (1957) made extensive measurements of free enthalpy changes of chemical reactions at higher temperatures. Similar potentiometric measurements of solid electrolyte cells are still made in the context of electrochemical sensors which are one of the most important technical applications for solid electrolytes. 

A wide number of sensor types have been described in the literature, from optical to mass spectrometry-based devices, but the sensors most commonly used in artificial tongues are electrochemical. 

Sensing of chlorine is possible with a phthalocyanine-based optode that is elec-trochemically reset [101]. Also a direct electrochemical Clark-type sensor employing carbon electrodes has been investigated [102]. For this type of sensor, the various types of carbon gave different responses and the edge-plane sites of graphitic electrodes were identified as electrochemically active. Both chlorine reduction and chlorine evolution were studied and the effects of the trichloride anion, Ch", were highlighted. 

FICs are useful as electrochemical sensors, electrolytes and electrodes in batteries and in solid state displays (Farrington Briant, 1979 Ingram Vincent, 1984). If a FIC material containing mobile M ions separates two compositions with different activities of M, a potential is set up across the FIC that can be related to the difference in the chemical activities of M. By fixing the activity on one side, the unknown activity on the other can be determined. This principle forms the basis of a number of ion-selective electrodes LaFj doped with 5% SrF2 is used for monitoring fluoride ion concentration in drinking water. Similarly, calcia-stabilized-zirconia is used in cells of the type... 

One of the goals in the chemically modified electrode research area has been to develop new types of electrochemical sensors. Several review articles have recently been published on this subject [86,87], Our intent is not to provide another review of this voluminous literature. Rather, we would like to introduce the reader to the concepts behind the use of chemically modified electrodes as electrochemical sensors. As we will see, the key to developing new sensors is... 

The most obvious way to incorporate this chemistry into an electrochemical sensor is to immobilize the enzyme onto an electrode surface and use this electrode to oxidize the hydrogen peroxide produced. An enzymatic sensor of this type was first prepared by Guilbault and Lubrano [91]. Numerous variations on this theme have since appeared, and sensors that employ this electrochemistry are now commercially available. 

With this group of electrochemical sensors, information is obtained from the current-concentration relationship. The two most important issues to discuss are (1) the origin of the signal for various types of amperometric sensors and (2) the origins of selectivity. To begin our examination of these issues, we briefly reiterate some of the information presented in the Introduction to Electrochemical Sensors (Chapter 5). 

The production of gas sensors. The production records of various types of gas sensors for past five years in Japan are listed in Table I except for the oxygen and humidity sensors. The sensors produced in the largest quantity are of the semiconductive type, followed by the catalytic combustion and thermistor types. These sensors have been mostly applied to domestic uses such as gas leakage alarms or gas control systems for LP gas and town gas which are extensively used for cooking and heating in Japanese houses. This is why these sensors are manufactured on a large scale. Other electrochemical sensors have been developed mainly to monitor other gases. 

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