Sensitivity field

The transfer impedance Zt between the CC electrode pair and the PU electrode pair is given by Eq. (6.39). The contribution of each voxel is P4ci-Jcc. and we define the sensitivity S of a tissue voxel as  

In a two-electrode system (bipolar or monopolar), the forward and reciprocal current densities are identical, so therefore  

Sensitivity may be defined according to any transfer function our interest is on impedance sensitivity. The spatial variation of S is the sensitivity field. At the neutral electrode in a unipolar system, J is low, so the contribution of the tissue there wiU be negligible. In a tube with cross-sectional area A and J = I/A constant, Eq. (6.41) reverts to the well-known R = pL/A. For the unipolar hemisphere on the tissue surface, Eq. (6.3) shows that J is proportional to r. From Eq. (6.41), Z is proportional to J p, and the contribution of a 

However, as long as we are inside the symmetrical zone of reciprocal current density, the contribution from the left and right side volumes with respect to the PU electrode position are equal but with opposite signs. The volume of the symmetrical zone is dependent on the reciprocal current path (e.g., whether it is a bipolar or unipolar PU electrode system). The paradox is that the symmetrical very high sensitivity region has zero net sensitivity all contributions cancel. In conclusion, such an electrode configuration will be very sensitive to asymmetry in the tissue near the PU electrode, and the recording may easily be unstable and noisy. Increased PU electrode contact area will reduce the problem, but this implies current disturbance of the J field. 

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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. 

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Shin JE. 1989. Evaluation of chemically-sensitive field-effect transistors for detection of organophosphorus compounds. Wright-Patterson AFB, OH Air Force Institute of Technology. NTIS No. AD-A215-536. 

Fig. 2.16. Ion-sensitive field effect transistor (intersection and symbol), (a) n-p-n transistor, (b) IGFET (MOSFET), (c) ISFET.

Apart from the sampling principle, sensor layouts can also be subdivided into point-probe sensors, giving averaged information about the analytes within the sensitive field, and imaging sensors, delivering a spatially as well as spectrally resolved image of the investigated area. 

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T. Uno, T. Ohtake, H. Tabata, and T. Kawai, Direct deoxyribonucleic acid detection using ion-sensitive field-effect transistors. Jpn. J. Appl. Phys. 43, L1584—L1587 (2004). 

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). 

Y.Q. Miao, J.G. Guan, and J.R. Chen, Ion sensitive field effect transducer-based biosensors. Biotech. Adv. 21, 527-534 (2003). 

Y.V. Plekhanova, A.N. Reshetilov, E.V. Yazynina, A.V. Zherdev, and B.B. Dzantiev, A new assay format for electrochemical immunosensors polyelectrolyte-based separation on membrane carriers combined with detection of peroxidase activity by pH-sensitive field-effect transistor. Biosens. Bioelectron. 19, 109-114(2003). 

M. Zayats, O.A. Raitman, V.I. Chegel, A.B. Kharitonov, and I. Willner, Probing antigen-antibody binding processes by impedance measurements on ion-sensitive field-effect transistor devices and complementary surface plasmon resonance analyses development of cholera toxin sensors. Anal. Chem. 74, 4763-4773 (2002). 

I. Freund, and B. Wolf, Non-invasive measurement of cell membrane associated proton gradients by ion-sensitive field effect transistor arrays for microphysiological and bioelectronical applications. Biosens. Bioelectron. 15, 117-124 (2000). 

Chemically modified waxes, 26 220 Chemically resistant fibers, 13 389 Chemically sensitive field-effect transistors (ChemFETs), 22 269. See also Field effect transistors (FETs)... 

Explain the main mechanistic differences between a glass membrane electrode and an ion-sensitive field effect transistor (ISFET). 

The measurement of changes of the surface potential Vo at the interface between an insulator and a solution is made possible by incorporating a thin film of that insulator in an electrolyte/insulator/silicon (EIS) structure. The surface potential of the silicon can be determined either by measuring the capacitance of the structure, or by fabricating a field effect transistor to measure the lateral current flow. In the latter case, the device is called an ion-sensitive field effect transistor (ISFET). Figure 1 shows a schematic representation of an ISFET structure. The first authors to suggest the application of ISFETs or EIS capacitors as a measurement tool to determine the surface potential of insulators were Schenck (15) and Cichos and Geidel (16). 

An application well-suited for IMS is the decommissioning and cleanup of sites where extensive manufacturing of explosives has taken place in the last century and where widespread contamination of soils and waters has occurred [74]. Decontamination of model metal scrap artificially contaminated with TNT and of decommissioned mortar rounds stiU containing explosives residue was followed by sampling surfaces with analysis by a portable mobility spectrometer. Mixed anaerobic microbial populations of bioslurries were employed in decontamination of scrap and the mortar rounds, and the IMS analyzer was seen as a sensitive field... 

J. Janata and R. J. Huber, Chemically sensitive field effect transistors. Chapter 3 of... 

ION-SELECTIVE ELECTRODES (ISEs) AND ION-SENSITIVE FIELD-EFFECT TRANSISTORS (ISFETs)... 

Liu et al. have reported the development and applications of the commonly used local anaesthetic sensitive field-effect transistor(FET) [56]. The ion-pair complexes of procaine with silicotungstate, tetraphenylborate, or reineckate were prepared as electroactive materials for a drug sensor. These active materials were coated onto the platinum draw wire of a MOSFET to make a local anaesthetic-sensitive FET that... 

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