Extinction coefficient fluorophores

The amount of fluorescence emitted by a fluorophore is determined by the efficiencies of absorption and emission of photons, processes that are described by the extinction coefficient and the quantum yield. The extinction coefficient (e/M-1 cm-1) is a measure of the probability for a fluorophore to absorb light. It is unique for every molecule under certain environmental conditions, and depends, among other factors, on the molecule cross section. In general, the bigger the 7c-system of the fluorophore, the greater is the probability that the photon hitting the fluorophore is absorbed. Common extinction coefficient values of fluorophores range from 25,000 to 200,000 M 1 cm-1 [4],... 

Measure the absorbance of the derivative at 495 nm. Determine the level of fluorophore incorporation by using its molar extinction coefficient. 

The spectral properties of this fluorophore are similar to those of other coumarin derivatives. The excitation maximum occurs at about 382nm and its emission peak at 472nm, producing light in the blue region of the spectrum. The extinction coefficient of DCIA at its wavelength of maximum absorbance, 382nm, is 33,000 M em-1 (in methanol). 

This fluorophore has an excitation maximum at 502 nm and an emission maximum at 510nm. The small Stoke s shift of only 8nm creates some difficulty in discrete excitation without contaminating the emission measurement with scattered or overlapping light. The extinction coefficient of the molecule in methanol is about 77,000M 1cm 1 at 502nm. 

The excitation maximum for the molecule occurs at 535 nm and its emission at 552 nm. Its Stoke s shift is slightly greater than some of the other BODIPY fluorophores, producing a 17nm separation between excitation and emission peaks. BODIPY 530/550 C3 has an extinction coefficient in methanol of about 62,000 M 1 cm-1 at 535 nm. 

These fluorophores have excitation maxima at 377-378 nm and at 398-399nm and emission maxima at 422-423 nm. The extinction coefficients of the molecules in water are about 27,000 M 1cm 1. The Cascade Blue derivatives can be used along with Lucifer Yellow... 

The spectral characteristics of Lucifer Yellow iodoacetamide produce luminescence at somewhat higher wavelengths than the green luminescence of fluorescein, thus the yellow designation in its name. The excitation maximum for the probe occurs at 426 nm and its emission at 530 nm. The rather large Stoke s shift makes sensitive measurements of emission intensity possible without interference by scattered excitation light. The 2-mercaptoethanol derivative of the fluorophore has an extinction coefficient at pH 7 of about 13,000 M cm-1 at 426nm. 

In choosing a fluorescent tag, the most important factors to consider are good adsorption (high extinction coefficient), stable excitation without photobleaching, and efficient, high quantum yield of fluorescence. Some fluorophores, such as fluorescein, exhibit rapid fluorescent quenching which lowers the quantum yield over time. Up to 50 percent of the fluorescent intensity observed on a fluorescein-stained slide can be lost within 1 month in storage. AMCA and... 

The photophysical properties (extinction coefficient, shifts in absorption and emission spectra, quantum yield, and lifetime) of a variety of probes are modified by pH changes, complexation by metal ions, or redox reactions. The resulting changes in photophysical parameters can be used to determine concentration of H+ and metal cations with suitably designed fluorophores. Most of these resulting sensors involve an equilibrium between the analyte, A, and the free probe (unprotonated or noncom-plexed by metal ion), Pf. If the stoichiometry of this reaction is 1 1, the reaction may be represented by... 

This fluorophore has an excitation maximum at 400 nm, and an emission maximum at 420 nm. The extinction coefficient of the molecule in aqueous solution at pH 7 is about 31,000 M em1. Cascade Blue hydrazide and Lucifer Yellow derivatives can be simultaneously excited by light of less than 400 nm, resulting in two-color detection at 420 and 530 nm. 

Squarylium dyes such as (83) [75] have probably received less attention than cyanine dyes due to the fact that the majority of syntheses furnish symmetrical species which are difficult to monofunctionalize in reactions such as the formation of peptide conjugates. The unsymmetrical types have been reported but seem to suffer from about 50% decrease in extinction coefficient. Squaiyliums are also more difficult to handle due to their low solubility. Very few water-soluble systems have been reported. These compounds are also used exclusively as fluorophores, but quantum yields are highly dependent on substituents and environment. 

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