Immunological sensors

Combined (e.g., transducer and analyte) amperometric urea sensor, immunologically sensitized field-effect transistor (IMFET), enzyme field-effect transistor (ENFET)... 

CHEMFET with antibody It has been shown that the immunological coupling response of some of these electrodes might be a minor component of the overall response, which would make these sensors difficult to use as immunoelectrodes In general, these electrodes as yet have insufficient sensitivity for most practical immunoassays. 

Enormous progress is being made in the development of amperometric sensors, based on enzyme catalysed reactions, in widely varying clinical and immunological diagnostic methods. 

Bio)chemical sensors can be active or passive according to whether they use a sensing microzone to accommodate a chemical or biochemical reaction and/or a biochemical e.g. immunological) or physico-chemical separation e.g. sorption). It should be noted that passive sensors e.g. a fibre-optic tip immersed in an industrial process stream) do not meet one of the essential requirements included in the definition of sensors as regeirds composition... 

It is known that chronic active inflammation in the gastric mucosa involves several interleukins (IL-8, IL-10 and IFN-gamma) known as immunological markers of the blood serum [33]. Hence it is possible that extensive gastric inflammation would lead to an increased release of some of the volatile inflammatory biomarkers in breath causing differences in the sensor response. 

Chemical sensors utilize the immunological recognition principle by coupling with optical, electrochemical, or other transducer (signal transfer) described e.g. by Eggins (1996) and Rogers et al. (1998). A tendency to miniaturized formats ( chips ) as part of the nanotechnology can be observed. 

An immuno sensor for determining specific proteins uses a liquid antigen containing cardiolipin, phosphatidyl choline, and cholesterol immobilized onto an acetyl cellulose membrane. The membrane-bound antigen retains immunological reactivity to Wasserman antibody. The asymmetrical potentitil is dependent on the concentration of the antibody (319, 320). 

Immunologically based sensors show great potential, but there are a number of problems that may limit their performance. For example, the nonspecific adsorption of proteins and other large molecules can adversely affect the a rent sensitivity and selectivity. Strategies for minimizing this effect include the use of a reference crystal coated with a protein that does not specifically interact with the antigen or compound of interest [27], and deactivation of nonspecific adsorption sites. 

A heterogeneous EIA coupled with a potentiometric electrode permitted the assay of BSA down to 10 ng/ml and cAMP down to 10 nmol/1 (Meyerhoffand Rechnitz, 1979). Urease was used as the marker enzyme and its activity was measured by means of an ammonia gas-sensing electrode. The equilibrium of the immunological reaction at the sensor was reached rather slowly. The advantage of the rapid response of biosensors could not therefore be exploited. 

The determination of antigens and antibodies can be improved by immobilization of the appropriate immunochemical partner of the analyte. When the immunological reaction can be rendered reversible the immobilized ligand becomes reusable. Whereas in immunoreactors the immunosorbent is separated from the sensor, in immunosensors both elements are in intimate physical contact. We shall show below that these devices can be used to perform the classical functions of immunoassays. 

Other, less specific potentiometric immunoprobes are based on the antigen-induced potential shift of chemically modified semiconductor electrodes (Fig. 125) (Yamamoto et al., 1983). The surface of a titanium dioxide electrode is covered by a BrCN-activated polymer membrane and inserted into an antibody-containing solution. The antibody binds covalently to the activated electrode surface. The antigen to be determined is added when the potential difference between the sensor and a reference electrode is stable. As a result of the immunological reaction a new... 

Immunoassays using piezoelectric detectors coated with antigen or antibody had been devised as early as 1972 (Shons et al., 1972). The mass increase resulting from the immunological complex formation leads to a measurable change of the resonance frequency of the piezoelectric crystal. Effects of temperature and electronic noise can be eliminated by using a pair of crystals. Such sensors are only applicable in the dry state. 

The in vivo application of glucose sensors is restricted by immunological reactions of the organism against the implanted material. The... 

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