High-resolution laser-induced fluorescence

New to the fourth edition are the topics of laser detection and ranging (LIDAR), cavity ring-down spectroscopy, femtosecond lasers and femtosecond spectroscopy, and the use of laser-induced fluorescence excitation for stmctural investigations of much larger molecules than had been possible previously. This latter technique takes advantage of two experimental quantum leaps the development of very high resolution lasers in the visible and ultraviolet regions and of the supersonic molecular beam. 

Lada, M.W., Vickroy, T.W., Kennedy, R.T. (1997). High temporal resolution monitoring of glutamate with aspartate in vivo using microdialysis on-line with capillary electrophoresis with laser-induced fluorescence detection. Anal. Chem. 69, 4560 1565. 

The high sample demands and low-throughput of LC-MS methods have led to the creation of a capillary electrophoresis (CE) platform for ABPP [48]. Proteomes are labeled with a fluorescent probe, digested with trypsin, and enriched with antifluorophore antibody resins. Use of CE coupled with laser-induced fluorescence (LIF) detection to analyze the enriched peptides resulted in far superior resolution to ID SDS-PAGE, particularly for enzymes that share similar molecular masses. Sensitivity limits of 0.05-0.1 pmol/mg proteome, negligible sample requirements (—0.01—0.1 pg proteome), and the ability to perform rapid CE runs in parallel with 96-channel instruments, make CE-based ABPP a potentially powerful technique. One drawback is that the identities of the probe-labeled proteins are not immediately apparent, and correlated LC-MS experiments must be performed to assign protein identities to the peaks on the CE readout. 

Laser-based spectroscopic probes promise a wealth of detailed data--concentrations and temperatures of specific individual molecules under high spatial resolution--necessary to understand the chemistry of combustion. Of the probe techniques, the methods of spontaneous and coherent Raman scattering for major species, and laser-induced fluorescence for minor species, form attractive complements. Computational developments now permit realistic and detailed simulation models of combustion systems advances in combustion will result from a combination of these laser probes and computer models. Finally, the close coupling between current research in other areas of physical chemistry and the development of laser diagnostics is illustrated by recent LIF experiments on OH in flames. 

By contrast, laser scattering methods now permit temperature composition and flow measurements that are both nonintrusive and give very high spatial resolution. These light scattering methods include laser Raman spectroscopy, laser-induced fluorescence, coherent Raman spectroscopy as well as laser velocimetry... 

The recent availability of tunable dye lasers has markedly enhanced our ability to inquire into the chemistry and physics of combustion systems. The high sensitivity, spectral and spatial resolution, and non-perturbing nature of laser induced fluorescence makes this technique well suited to the study of trace chemistry in complex combustion media. A barrier to the quantitative application of fluorescence to species analysis in flames has been the need to take into account or bypass the effects of quenching. The use of saturated fluorescence eliminates quenching as a problem and has the further advantage that fluorescence intensity is insensitive to variations in laser power (1, 2 ). However, the generation of high concentrations of excited states under saturated excitation in an active flame environment opens up the possibilities for laser induced chemistry effects that also must be taken into account or avoided (3,4,5). 

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