Chemical field effect sensors

Comparable is the CHEMFET (Chemical Field Effect Transistor), a chemical sensor on a FET, e.g., for H , Na, K and Ca2+ in blood, four CHEMFETs had been mounted on one plate [Clin. Chem., 30 (1984) 1361. 

A. Poghossian and M.J. Schoning, Silicon-based chemical and biological field-effect sensors, in Encyclopedia of Sensors (C.A. Grimes, E.C. Dickey, and M.V. Pishko, eds), Vol. 9, pp. 463-533. American Scientific Publisher, Stevenson Ranch, 2006. 

L.J. Bousse, N.F. de Rooij, and P. Bergveld, Operation of chemically sensitive field-effect sensors as a function of the insulator-electrolyte interface. IEEE Trans. Electron Dev. 30, 1263-1270 (1983). 

Xie D., Jiang Y, Pan W., Jiang J., Wu Z., and Li Y, Study on bis [phthalocyaninato] praseodymium complex/silicon hybrid chemical field-effect transistor gas sensor. Thin Solid Films, 406, 262-267, 2002. 

At a higher level of miniaturisation, work has been directed at constructing miniature electrochemical cells for biosensor applications (20). Chemical field effect transistors (CHEMFETs) and ion selective field effect translators (ISFETs) have received a high level of research interest for almost a decade ( but with little tangible results in terms of commercially available systems. Some recent research has been directed at integration of the sensor and control electronics into a discrete, disposable device (21). Although further development is still required, the... 

CNT-based gas sensors have shown good electrical response as well. It was established that chemiresistors and chemical field-effect transistors are probably the most promising types of gas sensors based on CNTs (Kong et al. 2000 Bondavalli et al. 2009 Wang and Yeow 2009 Zhang and Zhang 2009 Hu, et al. 2010). Typical configuration of such sensors is shown in Fig. 1.10. It has to be pointed out that for this kind of sensor the research has essentially focused on SWCNTs, because MWCNTs are only metallic and therefore unsuitable to fabricate chemiresistors and transistors. 

ChemFETs (chemical field effect transistors) combined with a reference electrode. Although the transducer principle varies from the potentiometric sensors, the result is comparable. 

Miniaturised sensors have been made which are able to be placed in small spaces using semiconductor technology. The various kinds of sensors include ion-selective field-effect transistors (ISFETs) and chemical field-effect transistors (ChemFETs), as well as chemiresistors. 

A ChemFET, a chemical field-effect transistor, is a type of FET that is a chemical sensor where the charge on the gate electrode is due to a chemical process. In principle, it may be used to detect atoms, molecules and ions in liquids and gases. For example, the SiOa gate material has Si-OH groups on the surface, which can be used for covalent attachment of organic molecules and polymers. 

Chemical and biological sensors (qv) are important appHcations of LB films. In field-effect devices, the tunneling current is a function of the dielectric constant of the organic film (85—90). For example, NO2, an electron acceptor, has been detected by a phthalocyanine (or a porphyrin) LB film. The mechanism of the reaction is a partial oxidation that introduces charge carriers into the film, thus changing its band gap and as a result, its dc-conductivity. Field-effect devices are very sensitive, but not selective. 

In recent years further concepts have been developed for the construction of polymer-based diodes, requiring either two conjugated polymers (PA and poly(A-methyl-pyrrole) 2 > or poly(A-methylpyrrole in a p-type silicon wafer solid-state field-effect transistor By modifying the transistor switching, these electronic devices can also be employed as pH-sensitive chemical sensors or as hydrogen or oxygen sensors 221) in aqueous solutions. Recently a PPy alcohol sensor has also been reported 222). 

Janata, J. Chemically Sensitive Field Effect Transistors, in Solid State Chemical Sensors (Janata, J., Huber, R. J., eds.) New York Academic Press 1985, p. 65... 

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. 

Polythiophenes (PTs)/CNTs composites have emerged as an intriguing system for use as photovoltaic devices and field effect transistors [57]. Swager and Bao independently reported methods for the assembling of PTs/CNTs systems and showed their great potential as transparent conductive films [58]. Another interesting application arises from the possibility to functionalize the polythiophene backbone for applications as chemical sensors [134]. 

CNTs can be easily doped by noncovalent means via molecular adsorption, an aspect that has been considerably exploited to develop ultrasensitive field effect transistor sensors [88-91]. However, substitutional doping with B and N to confer p and n character to the CNTs has also been carried out [92]. Such doped systems can be more susceptible to react with donors or acceptors molecules (depending on the doping) allowing the chemically reactivity to increase. 

Liu S, Shen Q, Cao Y et al (2010) Chemical functionalization of single-walled carbon nanotube field-effect transistors as switches and sensors. Coord Chem Rev 254 1101-1116... 

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