Chromogenic indicators

When analyzing an immunostained specimen, deposits of the colored chromogen indicate the presence of the antigen and represent specific positive staining. The pattern of staining in the cells can be cytoplasmic, nuclear, membranous, or surface focal or diffuse. This section addresses some of the most common problems encountered in immunoperoxidase procedures and the appropriate solutions to correct them (see Chapters 23-25). (See Note 4 for additional troubleshooting resources.)... 

Oximes and hydroxamic acids are frequently used as titrants, for masking, as metal-lochromic or chromogenic indicators as well as for spectrophotometric determinations. 

The chromogenic indicator should be selective for particular metal ions to reduce chemical interference. 

Cuprous iodomercurate [13876-85-2] Cu2Hgl4, is a bright red water-insoluble compound prepared by precipitation from a solution of K Hgl with cuprous chloride. It is used in temperature-indicating paints because it reversibly changes color to brown at 70°C (see Chromogenic materials). 

Chemical indicators for dry-heat steriliza tion are available either in the form of pellets enclosed in glass ampuls, or in the form of paper strips containing a heat-sensitive ink. The former displays its end point by melting, the latter by a color change (see Chromogenic materials). 

The simple spectrophotometric thiobarbituric acid (TBA) test has been frequently used for many years as an indicator of the peroxidation of PUFAs present in biological matrices. This test involves the reaction of aldehydes in the sample with TBA at c. 100°C under acidic conditions (Equation 1.13) to produce a pink-coloured chromogen, which absorbs light strongly at a wavelength of 532 nm (Nair and Turner, 1984). 

Is there any other approach or concept that can directly measure protein amount in the tissue section Ten years ago, Roth et al.38 documented a novel method, named the Midwestern assay. This method is based on using two chromogens, soluble and insoluble, for the IHC staining process, to produce sequential production of soluble and insoluble reaction products. The soluble IHC product is used to measure the amount of antigen (protein) by spectrophotometry, while insoluble product indicates the localization of protein in the tissue section. Their experimental results demonstrated that soluble reac-... 

Generally, sensors based on chromogenic or fluorogenic indicators are advantageous over sensors based on PSDs or ion-exchange/co-extraction. A... 

These slides are permanent and should not fade with time. If the presence of endogenons pigment is a problem with a particular specimen, or a color other than brown is desired as an indicator, different chromogenic compounds can be... 

The substance to be assayed—e.g., the hormone thyroxine in a serum sample—is pipetted into a microtiter plate (1), the walls of which are coated with antibodies that specifically bind the hormone. At the same time, a small amount of thyroxine is added to the incubation to which an enzyme known as the "tracer" (1) has been chemically coupled. The tracer and the hormone being assayed compete for the small number of antibody binding sites available. After binding has taken place (2), all of the unbound molecules are rinsed out. The addition of a substrate solution for the enzyme (a chromogenic solution) then triggers an indicator reaction (3), the products of which can be assessed using photometry (4). 

Residues of methylene blue in edible animal tissues are of public health concern because tliis dye and its metabolites are mutagenic (74). Metabolism studies in cattle have indicated that methylene blue can be eliminated in urine partly unchanged, partly metabolized to leucomethylene blue, or demethylated to N-methyl homologues of thionin, the completely demethylated metabolite of methylene blue, or reduced in vivo and subsequently eliminated in its leuco-form or in one or more chromogenic substances (75). 

The study indicated that the ground state of the molecule should be regarded as a resonance hybrid of (1) and (118) and that the basic chromogen is the H- chromophore... 

Screening. Primary screening is necessary to eliminate nonspecific hybridomas as soon as possible. Screening is also used to test the hybridoma culture supernatant for antibody reactivity and specificity. As an example, an Epstein-Barr virus associated protein is coated onto plastic ELISA plates. After incubation of hybridoma culture supernatant, secondary enzyme-labeled conjugate and chromogenic substrate, a colored product indicates a positive hybridoma. Alternatively, immunocytochemical screening can be used. It is preferable to test hybridomas when at least three-quarters of them are confluent. 

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