Transducers field effect transistor-based

Electroehemical transdueers are elassified as amperometric, potentiometric or conductometrie [8]. In addition we will here consider field-effect transistor-based transducers separately. Potentiometric sensors make use of the development of an electrical potential at the surface of an electrode when it is placed in a solution containing ions that can exchange with the surface. The potential of the electrode is... 

Novel glycerol and formaldehyde selective sensors based on pEI-Sensitive Field Effect Transistors as transducers and Glycerol Dehydrogenase and Formaldehyde Dehydrogenase as biorecognition elements have been developed. The main analytical parameters of the sensors have been investigated and will be discussed. 

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... 

Our choice for an Ion Sensitive Field Effect Transistor (ISFET) as a transducing element was based on the fact that the SiO surface contains reactive SiOH groups for the covalent attachment of organic molecules and polymers. In addition the FET has fast response times and can be made very small with existing planar IC technology. FIGURE 1... 

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) ... 

The direct fixation of the biocatalyst to the sensitive surface of the transducer permits the omission of the inactive semipermeable membranes. However, the advantages of the membrane technology are also lost, such as the specificity of permselective layers and the possibility of affecting the dynamic range by variation of the diffusion resistance. Furthermore, the membrane technology has proved to be useful for reloading reusable sensors with enzyme. In contrast, direct enzyme fixation is mainly suited to disposable sensors. This is especially valid for carbon-based electrodes, metal thin layer electrodes printed on ceramic supports, and mass-produced optoelectronic sensors. Field effect transistors may also be envisaged as basic elements of disposable biosensors. 

The activity of the cholinesterases can be determined directly using traditional spectrophotometric methods and also electrochemical techniques. Electrochemical methods for cholinesterase activity assay that are based on pH-shift potentiometry have been described (5-11). Conventional pH electrodes (7-11) and pH sensitive field effect transistors (5, 6) were employed as transducers coupled with cholinesterase enzymes. The main disadvantage of the pH-shift based method is a strong requirement for low buffer capacity of the sample. In addition, the sensitivity of pH based analytical techniques, in general, is less than that based on amperometric assay. The theoretical threshold of pH based assay methods is as low as 58 mV per decade of analyte concentration. Ion-selective membranes (12) and mediator-assisted potentiometry (13) have also been proposed for assays of cholinesterase inhibitors. 

Simon E, I ampe U, Pohle R, Fleischer M, Meixner H, Frerichs H-P, Lehmann M, Verhoeven H (2003) Novel carbon dioxide gas sensors based on field effect transistors. In Proceedings of the 12th Transducers 2003, Boston, MA, USA, June, p 204... 

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