Field-effect transistors biosensors

Figure 14.8 Two configurations of field-effect transistor biosensors (a) with a baek gate (b) with a water gate.

In modem history, particularly in the recent decades, liquid crystals (LCs) have become a very important class of materials. Since the first invention of LC display (LCD), LCs have become the quintessential materials in information displays such as TVs, computer monitors, and digital displays. In the recent development of LC materials, LCs have moved rapidly beyond display applications and are evolving into entirely new scientific frontiers, opening broad avenues for versatile applications such as lasers, photovoltaics, light-emitting diodes, field effect transistors, biosensors, switchable windows, and nanophotonics [1]. AU these applications benefit from LC s unique properties, e.g. self-organization and being able to... 

S. Varanasi, S. O. Ogundiran, and E. Ruckenstein, An algebraic equation for the steady state response of enzyme-pH electrodes and field effect transistors. Biosensors 3 269 (1988) and references therein. 

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

G.F. Blackburn, Chemically sensitive field-effect transistors, in Biosensors Fundamentals and Applications (A.P.F. Turner, I. Karube, and G.S. Wilson, eds), pp. 481-530. Oxford University Press, Oxford (1987). 

Field effect transistors are miniature, solid-state, potentiometric transducers (Figure 4.22) which can be readily mass produced. This makes them ideal for use as components in inexpensive, disposable biosensors and various types are being developed. The function of these semiconductor devices is based on the fact that when an ion is absorbed at the surface of the gate insulator (oxide) a corresponding charge will add at the semiconductor... 

Allen B, Kichambare P, Star A (2007) Carbon nanotube field-effect-transistor-based biosensors. Adv Mater 19 1439-1451... 

Researchers (Benilova et al., 2006 Arkhypova et al., 2008) are developing a biosensor-based pH-sensitive field-effect transistor technology for rapid determination of glycoalkaloids. The test takes advantage of the anticholinesterase activity of the glycoalkaloids. These tests could hold great promise, analogous to the ELISA test mentioned above. 

These electrodes must be distinguished from biosensors with enzymes at their surface. Electrodes constructed from field effect transistors (see 19.7) lead to voltametric detection. 

A particular type of biosensor can be developed by putting a membrane in contact with the semi-conducting layer of a field effect transistor. If the membrane incorporates an enzyme adapted to transform a particular analyte (Fig. 19.8), reaction of that enzyme will modify the polarity at the surface of the insulating layer. This will in turn modify the conduction between the source and the collector of the field effect transistor. The current flowing through these two electrodes (source and collector) serves as the signal. 

S.V. Dzyadevych, A.P. Soldatkin, Y.I. Korpan, V.N. Arkhypova, A.V. El skaya, J.-M. Chovelon, C. Martelet and N. Jaffrezic-Renault, Biosensors based on enzyme field-effect transistors for determination of some substrates and inhibitors, Anal. Bioanal. Chem., 377 (2003) 496-506. 

Carbon nanotubes, especially SWNTs, with their fascinating electrical properties, dimensional proximity to biomacromolecules (e.g., DNA of 1 nm in size), and high sensitivity to surrounding environments, are ideal components in biosensors not only as electrodes for signal transmission but also as detectors for sensing biomolecules and biospecies. In terms of configuration and detection mechanism, biosensors based on carbon nanotubes may be divided into two categories electrochemical sensors and field effect transistor (FET) sensors. Since a number of recent reviews on the former have been published,6,62,63 our focus here is mostly on FET sensors. 

The recently developed field-effect transistors (FETs)41 have also been used as biosensors. The ion-selective field-effect transistor (ISFET) uses ion-selective membranes, identical to those used in ion-selective electrodes, over the gate. 

In this chapter, we have proposed to use the acid-base properties of proteins as the transducing parameter in a biosensor. The acid-base behavior of proteins can reveal some important properties with respect to both their composition (selectivity) and their concentration (sensitivity). A change in this intrinsic parameter of the protein, when used as binding ligand, must be adequately determined. The classical method of acid-base determination is by volumetric titration. Successful application in a sensor requires another approach. Since the ion-sensitive field-effect transistor (ISFET) is suitable for fast (and local) pH detection, an 1SFET can be used for protein titration. 

The first biosensor based on semiconductor technology was reported by Caras and Janata in 1980 (1). They developed a microbiosensor sensitive to penidllin based on a hydrogen ion-sensitive field effect transistor (FET) transducer in conjunction with a penicillinase-immobilized membrane. This type of biosensor offers discriminating advantages over the conventional counterpart with an electrode transducer (see Chapter 3) ... 

Widespread interest has arisen in the potential of LB films as biosensors because many believe that the incorporation of biological molecules such as enzymes will lead to novel devices. Some are exploring the deposition of biologically active molecules onto the gate electrodes or oxides of field-effect transistors, but optical sensors, probably based on fiber optics, are the most favored technique. In all cases, the aim is to couple the specificity of inter-... 

Metal oxide semiconductor field effect transistors (MOSFETs) constitute other materials with applicability in the development of biosensors. Usually, a MOSFET structure consists of a metal gate on top of an oxide layer, tyqjically Si02 [189]. The catalytic properties of these sensors depend upon the type of the gate metal as well as the temperature at which the MOSFET is operated. The most used catalytic metals used as gate materials are Pd (is a good... 

---