Fluorescence direct

AFS quantifies the discrete radiation emitted by excited state atoms that have been excited by radiation from a spectral source. There are a number of mechanisms that are responsible for the atomic fluorescence signal resonance fluorescence, step-wise fluorescence, direct-line fluorescence, and sensitized fluorescence. Generally, the lowest resonance transition (l->0) is used for AFS. If a line source is used for excitation and if the atomic vapor is dilute, then the radiant power of the atomic... 

When an analyte is fluorescent, direct fluorometric detection is possible by means of a spectrofluorometer operating at appropriate excitation and observation wavelengths. This is the case for aromatic hydrocarbons (e.g. in crude oils), proteins (e.g. in blood serum, in cow milk), some drugs (e.g. morphine), chlorophylls, etc. Numerous fields of applications have been reported analysis of air and water pollutants, oils, foods, drugs monitoring of industrial processes monitoring of species of clinical relevance criminology etc. 

Most microscopes are designed so that some or all of the fight may be directed to either the binocular eyepieces for observation or to the camera for photography. To maximize the emitted fluorescence directed to the camera, a 0-100% reflector prism or mirror is a necessity. This arrangement allows one to direct 100% of the light to the camera when taking a picture. 

Diaminopyrimidines are used for antibacterial purposes. Although many of these compounds have some fluorescence, direct analysis is not useful because of the lack of sensitivity. The enhancement of the fluorescence of 2,4-diaminopyrimidines has been accomplished by treatment of the separated components with a solution of ammonium bisulfate [133], A fluorimetric method has also been developed for trimethoprim [2.4-diamino-5-(3,4, 5 -trimethoxybenzyl)pyrimidine] and its metabolites [134] which involves leaving the developed plates to stand for several days and then examining the increase in fluorescence. Amounts of ca. 10 ng could be detected after this time. 

This phenomenon may be considered as sensitized fluorescence. Direct contact is necessary for this phenomenon to take place. Siloxenes and similar compounds have many very remarkable properties. Not all observed effects can be explained and some explanations are presently tentative or speculative. 

Maretin CN-hydroxynaphthalimide diethyl phosphate) Cl) possesses enough natural fluorescence to be determined directly on tic. Mallet et a l C 1 2 ) proposed a method for its quantitative determination in water and milk by measuring the native fluorescence directly on a silica-gel tic. 

Fig. 16.9 (a) Concept of higher photon confinement at the tip apex by a nonlinear optical process. Efficiency of a first-order process such as spontaneous Raman or fluorescence directly reflects the field distribution at the tip apex while the efficiency of a second-order process such as SHG or SFG and a third-order process such as CARS shows further confinement due to the nonlinear response of the material, (b) Energy diagram of CARS process... 

Elements with low intensity fluorescence lines (e.g. Eu, Tm and Y) have been determined in aqueous solutions by depositing and drying nanoliter amounts of sample on the Ni cathode of a miniature GD source used as the atom reservoir [665], The atomic cloud thus formed was extited by a Cu-vapor laser-pumped dye laser to detect fluorescence directly. Absolute detection limits of 2 fg for Eu, 0.08 fg for Tm and 1.2 pg for Y were achieved and the total time for analysis from sample probing to data acquisition did not exceed 5 min. 

In general, the idealized molecular situation just discussed for fluorescence does not exist. That is, most polymers do not have a well defined absorption and emission ellipsoid. One exception to this case would be a polyene as has been described by Shindo, Read and Stein (59). As a result of this severe limitation, the technique cannot be directly applied to a polymer system. Instead, one generally mixes a very small amount of a fluorescent organic dye with the polymer ( 10 6 g/g polymer). It is the fluorescence from the dye that is measured and not fluorescence directly from the polymer molecule as would be desired. It is generally assumed that the axis of the dye molecule and the polymer... 

Laser-scanning microscopes can be classified by the way they excite and detect fluorescence in the sample. One-photon microscopes use a NUV or visible CW laser to excite the sample. Two-photon, or Multiphoton , microscopes use a femtosecond laser of high repetition rate. The fluorescence light can be detected by feeding it back through the scanner and through a confocal pinhole. The principle is termed confocal or descanned detection. A second detection method is to divert the fluorescence directly behind the microscope objective. The principle is termed direct or nondescaimed detection. 

In direct-line fluorescence, an atom is excited (usually from the ground state) by a radiation source, and then undergoes a direct radiational transition to a metastable level above the ground state. An example is absorption at the 283.31 nm line by ground-state lead atoms, with subsequent emission at 405.78 nm. Xs with resonance fluorescence, direct-line fluorescence may be excited by absorption of a nonresonance line (e.g., tin fluorescence at 333.06 nm). 

A fifth group of procedures includes the use of an array format. The usual 96-well plate for immunoassay measures the fluorescence in liquid phase either by determining the unbound fraction or by dissolving the bound reporter molecules to overcome problems related to autofluorescence, scattering, and back-reflection, although the selection of an appropriate solid support allows for the measurement of the fluorescence directly on the solid surface. For example, a heterogeneous fluoroimmunoassay using fluorescein-labeled antibodies for total thyroxin in serum uses this procedure. 

Photoluminescence can be used to detect an analyte in three ways (1) the analyte itself is intrinsically fluorescent (direct sensing) (2) the analyte can be tagged with a fluorophore label or (3) the analyte interacts with a luminescent probe. Direct sensing and fluorophore-tags are widely used in biomedical applications to probe cell environments. Many proteins are intrinsic fluorophores due to the presence of the aromatic amino acids tryptophan, phenylalanine and tyrosine. Analytes such as pH, CO2, NH3, O2 and various cations and anions can be measured indirectly using luminescence probes. 

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