Immunosensors enzyme-linked immunosorbent assay

With regard to immunosensors, a number of different reporter groups are used, including enzymes which convert a substrate into a highly coloured product (enzyme-linked immunosorbent assay, ELISA ) or which digest a substrate to give a photon of light to expose a film (chemiluminescence). 

On the basis of an enzyme thermistor, Mattiasson et al. (1977) developed one of the first immunosensors. Immobilized antibodies against albumin are placed in a column and set into an ET. After injection of an albumin-sample and a known amount of enzyme-labeled albumin, both are separated from the sample matrix by antibody-antigen-interaction. After injection of a substrate, the change in heat is a measure of analyte concentration. The less heat produced means that more albumin has been bound. An elution step regenerates the ELISA. Due to its thermal detection principle, the procedure is called TELISA (thermometric enzyme-linked immunosorbent assay). Figure 3 shows the principle of the TELISA procedure in its sandwich configuration. 

Although this method makes any washing steps superfluous, it is difficult to apply it in vivo because of the need for labelled antigens. Vo-Dinh and co-worker have described a portable fiber-optic monitor for use in combination with enzyme-linked immunosorbent assay [86] and a fiber-optic immunosensor for benzo[a]pyrene [101]. 

As mentioned above, GC and LC techniques (and GC-MS and LC-MS in particular) represent the major determinative approaches used in current MMRMs. Other, much less widely applicable and applied techniques include (1) capillary electrophoresis and capillary electrochromatography (2) thin-layer chromatography and (3) an array of immunoassays, such as immunosensors and enzyme-linked immunosorbent assay (ELISA). Immunoassays are, however, relatively useful for sensitive and rather rapid and inexpensive screening (followed by a confirmatory method in the case of a positive response) of selected pesticides for which ELISA kits or sensors are available. 

Historically, the immunoassay variant—the enzyme-linked immunosorbent assay (ELISA)—is a format where the enzyme label is followed optically as a change of absorbance, fluorescence or luminescence. The electrochemical immunoassays employ an electrode to measure the electroactive product released from a biocatalytic reaction of the label enzyme in this case, the immunoassay and electrode reaction occur at different surfaces. These concepts finally inspired various types of immunosensors where the immunorecognition event proceeds directly at the electrode surface. Thus, the electrochemical immunosensor is obtained when the immunorecognition element (antibody, antigen, hapten) becomes immobilised on the surface of the electrode as a transducer. The assays can be realised in the following formats ... 

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