Enzyme immunoassays advantages

Conventional ion-selective electrodes have been used as detectors for immunoassays. Antibody binding measurements can be made with hapten-selective electrodes such as the trimethylphenylammonium ion electrode Enzyme immunoassays in which the enzyme label catalyzes the production of a product that is detected by an ion-selective or gas-sensing electrode take advantage of the amplification effect of enzyme catalysis in order to reach lower detection limits. Systems for hepatitis B surface antigen and estradiol use horseradish peroxidase as the enzyme label and... 

GG is used extensively for analysis of antidepressants (Orsulak et al, 1989), but HPLC assays and enzyme immunoassays have become more popular in recent years. However, GC has advantages such as economy and ready availability. LCD and NPD generally are the detectors of choice (Coutts and Baker, 1982). NPD is relatively efficient for the analysis of tricyclic antidepressants (TCAs) as derivatization is not necessary, although the secondary, demethylated amines are sometimes derivatized to improve resolution and peak shape (Coutts and Baker, 1982). Acetylation, under aqueous or anhydrous conditions, followed by GC-NPD, has been used extensively for analysis of TCAs and the tetracyclic antidepressant maprotiline in plasma samples (Drebit et al., 1988). O Table 1-1 summarizes GC assays for some commonly prescribed antidepressants and their metabolites. 

Enzyme immunoassays using enzymes as markers have a number of advantages. Detection limits for enzymes are very low, because enzyme reactions can be amplified as catalytic reactions. The enzyme-labeled antigen and antibody are considerably stable. No expensive equipment is required to determine the enzyme activity. 

The effect of temperature on enzyme immunoassays should not be overlooked, and adequate thermo-static control is mandatory. This problem is not met with in other optical immunoassays which gives the latter some advantages. 

The use of enzyme labels in place of radioisotopes for the measurement of antigens, antibodies, and haptens has stimulated the new and expanding field of enzyme immunoassay (EIA). This technique has been the focus of several recent reviews, - and its merits compared to radioimmunoassay (RIA) have been discussed. In many cases, EIA can match RIA in terms of sensitivity and selectivity, yet has advantages of speed, convenience, and reduced cost. EIA sensitivity and simplicity is, however, dependent on the choice of enzyme label. It is the purpose of this work to introduce urease as a new enzyme label and to demonstrate the... 

Time-resolved fluorometry is versatile in its application. Applied in immunoassay, time-resolved fluorometry presents an unmatched combination of advantages. While sensitive and specific, radioimmunoassays present safety and stability problems. While safe, enzyme immunoassays lack sensitivity and dynamic range. 

Enzyme immunoassay methods offer a biological-based detection technique which is complementary to that of traditional residue analysis. Potential advantages must be evaluated in light of the intended application— use in a nationwide program for quantitatively measuring pesticide residues in foods. Ideally, each EIA method would contain simple, rapid extraction and cleanup (if required) steps, require minimal or portable equipment, be usable in the field by individuals with little scientific training, and produce quantitative results. 

Immunoassays vary by the different labels they use. The most common labels include chromophores, fluorophores, radioisotopes and enzymes. Of those labels, enzyme immunoassay or enzyme-linked immunosorbent assay (ELISA) is the most popular technique. ELISA has as an advantage the amplification of the analytical signal and/or increase of the sensitivity of the immunoassay. There are four types of ELISA direct ELISA, indirect ELISA, sandwich ELISA and competitive ELISA. 

The amplification of the amperometric response of redox species has been studied for p-aminophenol The sensitive detection of this compound is of particular interest since it is the basis for the measurement of enzymes such as alkaline phosphatase and (J-galactosidase, which are frequently used in enzyme immunoassays The electrode active species (p-aminophenol) is liberated in the enzyme catalysed hydrolysis of its aminophenylated substrate which itself exhibit an irreversible electrochemical behavior The utility of p-aminophenyl phosphate in enzyme immunoassays in combination with IDA electrodes has been demonstrated in [6] The unfavorable pH-optimum of alkaline phosphatase is the drawback of this system Because of its neutral pH-optimum p-galactosidase appeared to be more advantageous An illustration of the proposed electrochemical enzyme immunoassay is given in Fig 2... 

Enzyme immunoassay (EIA) is an alternative analytical procedure to radioimmunoassay which takes full advantage of the specificity and sensitivity that result from the use of an antibody but does not employ a radioactive isotope. 

Several types of labels have been used in immunoassays, including radioactivity, enzymes, fluorescence, luminescence and phosphorescence. Each of these labels has advantages, but the most common label for clinical and environmental analysis is the use of enzymes and colorimetric substrates. 

As an alternative, extremely sensitive detection can be achieved with reporter antibody probes tagged with intensely SERS-active compounds or with enzymes that react with substrates to yield SERS-active products. These methods often involve sandwich immunoassay techniques, which increase the number of required steps but offer the advantages of excellent sensitivity and the potential for label multiplexing. For example, Nie and coworkers recently reported the simultaneous detection of two types of antigens in a... 

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