Fluorescers fluorescein

Instruments of this type may also be used quite effectively to evaluate kinetics of time-dependent changes in foods, be they enzymatic or reactive changes of other types. The computerized data-acquisition capabilities of these instruments allow precise measurement of absorbance or fluorescence changes, often over very brief time periods ( milliseconds). This is particularly useful for analysis of fluorescence decay rates, and in measurement of enzymatic activity in situ. A number of enzyme substrates is available commercially which, although non-fluorescent initially, release fluorescent reaction products after hydrolysis by appropriate enzymes. This kinetic approach is a relatively underused capability of computerized microspectrophotometers, but one which has considerable capability for comparing activities in individual cells or cellular components. Fluorescein diacetate, for example, is a non-fluorescent compound which releases intensely fluorescent fluorescein on hydrolysis. This product is readily quantified in individual cells which have high levels of esterase [50]. Changes in surface or internal color of foods may also be evaluated over time by these methods. 

Yellow Dyes with Blue/Green Fluorescence. Fluorescein, C.I. Solvent Yellow 94, 45350 1 [518-45-6] (2), is perhaps the best known example, but equally important are coumarins, such as C.I. Basic Yellow40 [12221-86-2], and especially naphtha-limides such as C.I. Solvent Yellow44, 56200 [2478-20-8] (3). 

This assay is used to measure cell viability. It is a two-color fluorescence assay that simultaneously determines live (viable) and dead (nonviable) cells Live cells have intracellular esterases that convert nonfluorescent, cell-permeable fluorescein di-O-acetate to the intensely fluorescent fluorescein (green). Cleaved fluorescein is retained within cells. Dead cells have damaged membranes propidium iodide enters damaged cells and is fluorescent when bound to nucleic acids. It produces a bright red fluorescence in damaged or dead cells. 

Polyphenylene ether water loss regulator Carboxymethyl hydroxyethyl cellulose water marker, fluorescent Fluorescein water pipe, hot/cold Polyvinyl chloride, chlorinated water pumping equip. 

Boc- and Fmoc-terminated fluorescent fluorescein PNA monomer units were synthesized by means of solid-phase synthesis, and the products had photophysical properties comparable to nonmodifled fluorescein conjugates. 2-Aminopurine (2-ap) was the first fluorophore incorporated into a PNA strand for the purpose of examining PNA-DNA complexation via fluctuation in fluorescence emission. A more sophisticated sensing design was introduced by Seitz et al. that utilized the intercalator dye thiazole orange, termed a forced intercalation probe (FIT probe), for the determination of base pair mismatches within a duplex. ... 

One of the most widely used photo-chemicals for pH measmement is fluorescein [6], which displays complex optical properties dependent upon its ionic form (See Chap. 4, compound 4.3). In particular only the two anionic forms present at high pH are fluorescent. Fluorescein can be used a wavelength ratiometric probe... 

In a series of experiments it has been shown that it is possible to prepare giant POPC vesicles by the electroformation method in the presence of (non-fluorescent) fluorescein diphosphate, a substrate for alkaline phosphatase. The vesicles thus formed contained in the interior aqueous space substrate molecules which, after... 

Base catalysed oxidation of simple aryl carboxylic acid esters has been studied [31, 32[ and light is emitted in the presence of fluorescers [33]. The quantum yield is low (0CL = 10 ) and an electron transfer chemiluminescence seems likely in view of the order of efficacy of the fluorescers, fluorescein > 9,10-diphenyl anthracene 9,10-dibromoanthracene. 

I. Fluorescein test. Fuse together carefully in a dry test-tube for about 1 minute a few crystals of resorcinol and an equal quantity of succinic acid or a succinate, moistened with 2 drops of cone. H2SO4. Cool, dissolve in water and add NaOH solution in excess. A red solution is produced which exhibits an intense green fluorescence.-f-... 

Fluorescein reaction. Repeat Test i, using however resorcinol instead of phenol. A reddish solution having an intense green fluorescence is produced. 

Fluorescein reaction. Fuse together in a dry test-tube o-i g. of succinimide, O l g. of resorcinol and 2 drops of cone. HjSOi, Cool, add water and then NaOH solution in excess. A green fluorescent solution is obtained. 

EIA was originally developed as a histological technique to localize specific ceUular sites using the specificity of an immunological reaction (23). The resulting fluorescent antibodies can be detected in animal tissues at levels as low as 1 /tg/mL of body fluid. Eluorophore-labeled antibodies have also been used widely for flow cytometry appHcations using fluorescein antibodies to cell surface markers to detect and quantify specific cells (24). 

C is the concentration of limiting reactant in mol/L, c is the chemiluminescence quantum yield in ein/mol, and P is a photopic factor that is determined by the sensitivity of the human eye to the spectral distribution of the light. Because the human eye is most responsive to yellow light, where the photopic factor for a yellow fluorescer such as fluorescein can be as high as 0.85, blue or red formulations have inherently lower light capacities. 

Utilization of resonance effects can facilitate unenhanced Raman measurement of surfaces and make the technique more versatile. For instance, a fluorescein derivative and another dye were used as resonantly Raman scattering labels for hydroxyl and carbonyl groups on glassy carbon surfaces. The labels were covalently bonded to the surface, their fluorescence was quenched by the carbon surface, and their resonance Raman spectra could be observed at surface coverages of approximately 1%. These labels enabled assess to changes in surface coverage by C-OH and C=0 with acidic or alkaline pretreatment [4.293]. 

Note The full fluorescence intensity usually only develops about 30 min after the dipping process it then remains stable for several days if the chromatograms are stored in the dark (1, 5]. Fluorescein sodium can be employed in the reagent in place of 2, 7 -dichlorofluorescein [5]. The detection limits lie in the lower nanogram to picogram range [1, 5]. 

Discussion. This method is based upon the formation of a fluorescent chelate between calcium ions and calcein [fluorescein bis(methyliminodiacetic acid)] in alkaline solution.29 The procedure described below30 has been employed for the determination of calcium in biological materials.31 ... 

Fluorescent materials are very important in medical research. Dyes such as fluorescein (21) can be attached to protein molecules, and the protein can be traced in a biological system by exciting the fluorescein and looking for its emissions. The use of a fluorescent material allows the detection of much smaller concentrations than would otherwise be possible. Because fluorescent materials can be activated by radioactivity, they are also used in scintillation counters to measure radiation (see Box 17.2). 

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