Field-effect transistor chemically selective

There are now commercially available versions of the so-called chemical nose where multiple sensing elements are used to pick out specific chemicals in the aroma commodities such as beverages and perfumes. Most mi-croanalytical techniques have been reproduced at a research level in an on-chip format. These include the selective detection systems, such as field effect transistors, ion-selective electrodes, biosensors, bioassays, and acoustic wave mass dectors. 

Kolesar ES, Wiseman JM. 1991. Selective detection of nitrogen-dioxide and diisopropyl methylphosphonate with an interdigitated gate electrode field-effect transistor (IGEFET). Sensors and Actuators B - Chemical 5(l-4) 37-46. 

The silver(I) complexes with the tetrakis(methylthio)tetrathiafulvalene ligand have been reported, the nitrate salt presents a 3D structure with an unprecedented 4.16-net porous inorganic layer of silver nitrate,1160 the triflate salt presents a two interwoven polymeric chain structure.1161 The latter behaves as a semiconductor when doped with iodine. With a similar ligand, 2,5-bis-(5,5,-bis(methylthio)-l,3,-dithiol-2 -ylidene)-l,3,4,6-tetrathiapentalene, a 3D supramolecular network is constructed via coordination bonds and S"-S contacts. The iodine-doped compound is highly conductive.1162 (Methylthio)methyl-substituted calix[4]arenes have been used as silver-selective chemically modified field effect transistors and as potential extractants for Ag1.1163,1164... 

Clever chemists have designed electrodes that respond selectively to specific analytes in solution or in the gas phase. Typical ion-selective electrodes are about the size of your pen. Really clever chemists created ion-sensing field effect transistors that are just hundreds of micrometers in size and can be inserted into a blood vessel. The use of electrodes to measure voltages that provide chemical information is called potentiometry. 

Successful operation of potentiometric chemosensors opened up the possibility for the fabrication of chemical field-effect transistors (chemFETs) and ion-selective field-effect transistors (ISFETs). A sensing element in these devices, i.e. the MIP film loaded with the molecular, neutral or ionic, respectively, imprinted substance is used to modify surface of the transistor gate area. Apparently, any change in the potential of the film due to its interactions with the analyte alters the current flowing between the source and drain. 

Symmetrical placement of the ion-selective membrane is typical for the conventional ISE. It helped us to define the operating principles of these sensors and most important, to highlight the importance of the interfaces. Although such electrodes are fundamentally sound and proven to be useful in practice, the future belongs to the miniaturized ion sensors. The reason for this is basic there is neither surface area nor size restriction implied in the Nernst or in the Nikolskij-Eisenman equations. Moreover, multivariate analysis (Chapter 10) enhances the information content in chemical sensing. It is predicated by the miniaturization of individual sensors. The miniaturization has led to the development of potentiometric sensors with solid internal contact. They include Coated Wire Electrodes (CWE), hybrid ion sensors, and ion-sensitive field-effect transistors. The internal contact can be a conductor, semiconductor, or even an insulator. The price to be paid for the convenience of these sensors is in the more restrictive design parameters. These must be followed in order to obtain sensors with performance comparable to the conventional symmetrical ion-selective electrodes. 

Fig. 6.31 Insulated gate field-effect transistor (IGFET) with electronically conducting, chemically selective gate...

Cobben, P., Egberink, R. J. M., Bomer, J. G., Bergveld, P., Verboom, W., Reinhoudt, D. N., Transduction of selective recognition of heavy-metal ions by chemically modified field-effect transistors (chemfets). J. Am. Chem. Soc. 1992, 114, 10573-10582. 

In this chapter our work is described that deals with the development of chemically modified Field Effect Transistors (CHEMFETs) that are able to transduce chemical information from an aqueous solution directly into electronic signals. The emphasis of this part of our work will be on the materials that are required for the attachment of synthetic receptor molecules to the gate oxide surface of the Field Effect Transistor. In addition the integration of all individual components into one defined chemical system will be described. Finally, several examples of cation selective sensors that have resulted from our work will be presented. 

The integration of chemically sensitive membranes with solid-state electronics has led to the evolution of miniaturized, mass-produced potentiometric probes known as ion-selective field effect transistors (ISFETs). The development of ISFETs is considered as a logical extension of coated-wire electrodes (described in Section 5.2.4). The construction of ISFETs is based on the tech-... 

Although not an ion, glucose can be detected by virtue of an MIP-derived ion. The pH electrode is simply an ISE for H". Glass and ion-selective field effect transistors pH electrodes are the best characterised and the most successful ISEs. Many sensors employ chemical reactions to produce H" or OH ions and employ pH electrodes for signal transduction. An imprinted sensor based on this approach is the glucose sensor produced by Arnold s group [10]. This polymer employs a metal ion (Cu " ) in the imprinted site and makes use of the metal s... 

Future directions for FIA include improved methods for determining concentrations in FIA (i9, 20), an advanced modular system using fiber optics or ion-selective field-effect transistors in the detectors (20), and a system of solid microconduits for handling the solutions (20). These developments suggest even greater reductions in the size and cost of automated chemical analyses. 

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