Biosensors enzyme-linked immunosorbent assay

Test strips, which are available for the determination of about ten low-molecular mass substances (metabolites, drugs, and electrolytes) and eight enzymes [356], can be considered as precursors of optoelectronic biosensors. Efficient optoelectronic sensors based on immobilized dyes have been devised for the determination of glucose, urea, penicillin, and human serum albumin [357]. Other approaches use immobilized luciferase or horseradish peroxidase to assay ATP or NADH or, when coupled with oxidases, to measure uric acid or cholesterol. These principles have not yet been generally accepted for use in routine analysis. Thermistor devices involving immobilized enzymes or antibodies for a number of clinically relevant substances have also been described. Thermometric enzyme linked immunosorbent assays are being routinely employed for monitoring the production of monoclonal antibodies. 

The precision of the measurements ranged from 1.9% to 8.2% relative standard deviation, and the detection limit was 3 ng/mL for all analytes. The results compare quite favorably (2.4%-6.S% difference) with results from commercial single-analyte assays using spectroscopic enzyme-linked immunosorbent assays (ELISAs). In this application, four analytes were determined in duplicate, but any combination of up to eight analytes may be determined simultaneously. It is anticipated that when the array biosensor is coupled with a microfiuidics system (Section 33C) for solution handling, the combined device will become a powerful tool for the routine determination of this important class of biochemical analytes. 

The ICMs used for pesticide analysis include immimoassays (lAs) and the use of antibodies for sample preparation (e.g., for SPE and the cleanup of samples) [153], detection in flow-injection analysis, and biosensors. The earliest ICMs to be developed for pesticides analysis were lAs. There are various t) es of lAs, but the most frequently used in this context is the enzyme-linked immunosorbent assay (ELISA) [185]. ELISA is a heterogeneous assay because the antibodies or antigens are immobilized on a solid phase. Table 18.3 lists selected ELISA methods for the determination of pesticides in water samples [186-190]. Bjamason et al. have proposed an enzyme flow immunoassay (EFIA) using a protein G column for the determination of triazine herbicides in surface and wastewaters with a linear range between 0.1 and 10 pg/L [191]. 

Temperature sensors, such as the thermistors and thermopiles described in 4.4.4, can be used to monitor the variation in enthalpy arising from a reaction catalysed by an enzymatic label on either an andgen or an andbody. This technique is called TELISA (thermometric enzyme linked immunosorbent assay), and involves the use of reactor columns lined with antibodies, which detect antigens such as albumin [261]. These reactors, however, are not real biosensors. 

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