Luminescence spectroscopy advantage

Table 5.12 shows the main features of luminescence spectroscopy. The much higher sensitivity and specificity of luminescence techniques compared to absorption techniques is an obvious advantage for excitation spectra. In solution studies, pg ml. 1 levels can often be determined, as compared to p,gmL-1 levels in absorption spectroscopy. The greater sensitivity of luminescence techniques stems from the fact that the... 

The Introduction chapter contains the basic definitions of the main scientific terms, such as 5pectro5copy, luminescence spectroscopy, luminescent mineral, luminescent center, luminescence lifetime, luminescence spectrum and excitation spectrum. The state of the art in the steady-state luminescence of minerals field is presented. The main advantages of the laser-induced time resolved technique in comparison with the steady-state one are shortly described. 

Luminescence spectroscopy, whenever applicable, has the advantage that the low-temperature spectrum consists of only one electronic transition, whereas in absorption the transitions to the four spin-orbit components of g are superimposed. As a result the absorption spectrum is not as well resolved. 

A limitation of the application of luminescence spectroscopy to the analysis of real samples is its lack of specificity owing to similarities in spectral bandshapes and spectral positions of the luminescence spectra of many compounds. An obvious solution to this problem is the separation of the analytical sample s interfering constituents from each other before quantitation by fluorescence. High-performance liquid chromatography (HPLC) and related separation methods can be coupled to fluorescence spectroscopy to take advantage of the sensitivity of the spectroscopic method and the specificity of the separation method. 

Luminescence spectroscopy may be divided into two major areas fluorescence spectroscopy and phosphorescence spectroscopy. The differences between the two are based mostly on the time frames on which the phenomena of fluorescence and phosphorescence occur, phosphorescence decaying much more slowly (often taking several seconds) than fluorescence subsequent to excitation. Slight differences between the instrumentation used to observe fluorescence and that to observe phosphorescence take advantage of the temporal distinction between the two luminescence phenomena. Chemiluminescence is a form of fluorescence differing only in the fact that a chemical reaction as opposed to incident light generates the excited state. 

An advantage of luminescence spectroscopy, as with all emission systems, is flexibility of geometry of the sample that permits front surface viewing. That is, opaque or geometrically irregular specimens may be sampled directly (28). 

The problem seems to call for a new approach to the measurement of the small currents. We have carried out research on a scheme designed to take advantage of well-developed methods for the precise measurement of fast transients in luminescence spectroscopy. By transducing the electrochemical cell current to a photon flux, instead of a voltage, one transforms an electrochemical measurement with a difficult electronic solution into an optoelectronic problem with several known solutions. 

A big advantage of the solid-solid technique is the possibility of obtaining complexes that are not obtainable from solution. It must, however, be shown that uniform complexes rather than microcrystalline mixtures occur. Apart from X-ray powder diffraction (which does not properly account for very small crystallites), proof is obtained by solid-state spectroscopy (IR, UV, luminescence) or, in the case of stable radicals, by magnetic susceptibility measurements. The 1 1 and 2 1 complexes 68-72 were prepared by stoichiometric milling and relevant physical properties are collected in Table 3 [20]. 

In absorption spectrometry, <7i is usually fairly constant, and x1 fitting has no advantages. Typical examples of data with nonconstant and known standard deviations are encountered in emission spectroscopy, particularly if photon counting techniques are employed, which are used for the analysis of very fast luminescence decays [27], In such cases, measurement errors follow a Poisson distribution instead... 

Because of the complex and often overlapping principles behind kinase and phosphatase assays, I will review the principles of the various fluorescent and luminescent technologies. A textbook by Joseph R. Lakowitz (1999) titled Principles of Fluorescence Spectroscopy is recommended for detailed information on the biophysics of fluorescence. Olive (2004) and Von Ahsen and Boemer (2005) wrote good reviews on the advantages and disadvantages of various luminescent (including fluorescent) technologies for kinase assays. 

Analytical absorption spectroscopy in the ultraviolet and visible regions of the elechomagnetic spectrum has been widely used in pharmaceutical and biomedical analysis for quantitative purposes and, with certain limitations, for the characterisation of drugs, impurities, metabolites, and related substances. By contrast, luminescence methods, and fluorescence spectroscopy in particular, have been less widely exploited, despite the undoubted advantages of greater specificity and sensitivity commonly observed for fluorescent species. However, the wider availability of spectrofluorimeters capable of presenting corrected excitation and emission spectra, coupled with the fact that reliable fluorogenic reactions now permit non-fluorescent species to be examined fluorimetrically, has led to a renaissance of interest in fluorimetric methods in biomedical analysis. 

Figure 13.2 Principles of (a) time-resolved spectroscopy, (h) heterogeneous immunoassays, and (c) homogeneous immunoassays [1]. (Reproduced from J.C.G Bunzli and C. Piguet, Taking advantage of luminescent lanthanide ions, Chemical Society Reviews, 34, 1048—1077, 2005, by permission of The Royal Society of Chemistry.)...

In the last two decades the coordination chemistry of these elements has benefited greatly from advances in time-resolved laser fluorescence (TRLIFS) and synchrotron-based X-ray absorbance spectroscopies (XANES and XAFS). The advantageous luminescence properties of Am and... 

To extend the pressure range and also because of the advantages of precise pressure calibration by the ruby-luminescence technique, gasketed DACs have also found wide application for high-pressure Mossbauer spectroscopy... 

Most optical detection methods for biosensors are based on ultra-violet (UV) absorption spectrometry, emission spectroscopic measurement of fluorescence and luminescence, and Raman spectroscopy. However, surface plasmon resonance (SPR) has quickly been widely adopted as a nonlabeling technique that provides attractive advantages. Fueled by numerous new nanomateiials, their unique, SPR-based or related detection techniques are increasingly being investigated [28-31]. 

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