Labeled antigen

The simplest homogeneous ECIA formats have employed an amperometrically detectable antigen label. The pioneering work for this approach was again provided by Breyer and Radcliff vide supra. Since this early work, ferrocene has been... 

The tuneable nature of the evanescent field penetration depth is critical to the effective operation of this sensor as it facilitates surface-specific excitation of fluorescence. This means that only those fluorophores attached to the surface via the antibody-antigen-labelled antibody recognition event... 

Despite many novel developments in immunoassay design the principles are confined to two broad approaches those that rely on the competition between antigens labelled with a molecule which may be readily observed (for example, a radioisotope) and unlabelled antigens for a limited number of antibody binding sites and those in which the antibody is available in excess and for which there is no competition for binding sites. 

Test + Enzme- + Antibody — Antigen-antibody complexes antigen labelled... 

Fig. 1. Flowchart of an intracellular antigen labeling protocol. Abbreviations as in text.

Additionally, two studies have measured colorectal epithelial cell proliferation and apoptosis in human non-neoplastic mucosa in combination with serum bile acid quantification. Ochsenkuhn et al have reported a positive correlation between serum DCA levels and proliferation measured by flow cytometric cell cycle analysis. However, a more recent study of colorectal adenoma patients failed to detect a correlation between serum DCA and immuno-histochemical Ki-67 antigen labelling. Instead, this latter study revealed a positive correlation between serum DCA and the degree of TUNEL-positive epithelial cell apoptosis. ... 

The amperometric immunosensors reported so far rely on various methodological principles including use of a Clark electrode for detecting oxygen formation or depletion, an electrochemically active product yielded in an enzyme reaction or an antigen labelled with an electroactive species. 

Grassi, J., Frobert, Y., Lamourette, P, andLagoutte, B. (1988) Screening ofmono-clonal antibodies using antigens labeled with acetylcholinesterase application to the peripheral proteins of photosystem 1. Anal Biochem 168, 436-450... 

Most electrochemical immunosensors use antibodies or antigens labelled with an enzyme that generates an electroactive product which can be detected at the electrochemical transducer surface. The combination of high enzyme activity and selectivity with the sensitive methods of electrochemical detection provides a basis for the development of immunosensors. Horse radish peroxidase (HRP) and alkaline phosphatase (AP) are popular enzyme labels and can be used with a variety of substrates. 

Antigen labelled concentration this has to be in limiting amount to saturate the antibodies immobilised on the solid phase. 

Figure 4.12 describes two popular antibody microarrays formats that are constructed for antigen capture in small sample volumes with detection by either sandwich immunoassay or antigen labeling. In sandwich immunoassay, capture antibodies are arrayed and immobilized to select specific proteins which are then found by a second labeled detection antibody. In protein target labeling, all proteins in the sample are prelabeled (i.e., fluorescent dyes) prior to capture by immobilized antibody arrays. In direct assay systems, sample proteins are directly immobilized onto... 

Screening of Monoclonal Antibodies Using Antigens Labeled with Acetylcholinesterase... 

The most sensitive approach to surface antigen labeling is to incubate cells at 4°C while alive with antibodies. This prevents internal labeling background and also minimizes artifacts seen with some fixation. However, there are situations in which living cells are not available or the antigen of... 

HOIA using an antigen labeled enzyme modulator... 

Homogeneous, AM assays pose different requirements. Here, the enzyme should be easily conjugated near the active site without altering its activity. The reaction of hapten- or antigen-labeled enzyme with antibody should affect strongly the enzyme activity, e.g., through steric inhibition of the substrate at the catalytic site. The requirements for optimal ionic conditions and temperature for both enzyme activity and antigen-antibody interaction should be compatible. 

The estimation of an antibody in a liquid medium utilizes the specific antigen labelled with an isotope (generally I) Ag added in excess. The association Ag -Ab, soluble under these conditions, is separated by precipitation with 50% ammonium sulfate or a general anti-Ig antibody. Radioactivity of the precipitate is measured. 

FIGURE 15.6 Carcinoembryonic antigen labeling in ductal adenocarcinoma, with areas of well-defined tubule formation showing more luminal surface labeling. Non-neoplastic glands are often negative or only focally positive for this marker. However, it should be kept in mind that overlaps occur. 

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