Fluorescence laser based

The first half of this section discusses the use of the crossed beams method for the study of reactive scattering, while the second half describes the application of laser-based spectroscopic metliods, including laser-mduced fluorescence and several other laser-based optical detection teclmiques. Furtlier discussion of both non-optical and optical methods for the study of chemical reaction dynamics can be found in articles by Lee [8] and Dagdigian [9]. 

Van Den Beld, C. M. B. and Lingeman, H., Laser-based detection in liquid chromatography with emphasis on laser-induced fluorescence detection, Pract. Spectrosc., 12, 237, 1991. 

In a second experiment, Cy5-labelled antiBSA antibodies were immobilised on a silanised glass slide precoated with metallic nanoislands using a polydimethylsiloxane (PDMS) flow-cell. The antibody solution was left for 1 hour to attach and then the cell was flushed with deionised water. The slide was then dried with N2. For this experiment, a portion of the slide was not coated with metallic nanoislands, in order to act as a reference. Figure 20 shows the image recorded using the fluorescence laser scanner mentioned previously. The enhancement in fluorescence emission between those areas with and without nanoislands (B and A, respectively) is again evident. For both chips, an enhancement factor of approximately 8 was recorded. There is considerable interest in the elucidation and exploitation of plasmonic effects for fluorescence-based biosensors and other applications. 

Vukjovic et al.199 recently proposed a simple, fast, sensitive, and low-cost procedure based on solid phase spectrophotometric (SPS) and multicomponent analysis by multiple linear regression (MA) to determine traces of heavy metals in pharmaceuticals. Other spectroscopic techniques employed for high-throughput pharmaceutical analysis include laser-induced breakdown spectroscopy (LIBS),200 201 fluorescence spectroscopy,202 204 diffusive reflectance spectroscopy,205 laser-based nephelometry,206 automated polarized light microscopy,207 and laser diffraction and image analysis.208... 

Figure 11.15. Schematics of the optical arrangement and temperature probes for the Cr+ fluorescence lifetime-based fiber optic thermometers. F = short-pass optical filter Fa = bandpass or long-pass optical filter LD = laser diode LED = light emitting diode S = the fluorescence material used as sensing element vm = signal to modulate the output intensity of the excitation light source v/= the detected fluorescence response from the sensing element.

The subsequent development of laser diode sources at low cost, and improved electronic detection, coupled with new probe fabrication techniques have now opened up this field to higher-temperature measurement. This has resulted in an alexandrite fluorescence lifetime based fiber optic thermometer system,(38) with a visible laser diode as the excitation source which has achieved a measurement repeatability of l°C over the region from room temperature to 700°C, using the lifetime measurement technique. 

When compared to fluorescence detectors for HPLC, the design of a fluorescence detector for CE presents some technical problems. In order to obtain acceptable sensitivity, it is necessary to focus sufficient excitation light on the capillary lumen. This is difficult to achieve with a conventional light source but is easily accomplished using a laser. The most popular source for laser-induced fluorescence (LIF) detection is the argon ion laser, which is stable and relatively inexpensive. The 488-nm argon ion laser line is close to the desired excitation wavelength for several common fluorophores. The CLOD for a laser-based fluorescence detector can be as low as 10 12 M. 

A quite different group of experiments is concerned with the investigation of dye lasers themselves, or of lasers based on the photodissociation of molecules. Studies of the time behavior, concentration, or pressure and temperature dependence of fluorescence and... 

Photochemical Stability and the Wavelength of Excitation. Cyanines of chain length beyond Cy3 snffer from increasing photochemical instability. This can be a problem when they are nsed in conjunction with solid-state lasers operating around 630-650 nm. To overcome these problems workers at Boehringer Mannheim have developed the so-called pentacyclic fluorescent labels based on either the oxazine or rhodamine ring systems, e.g. Light Cycler Red 640 NHS (3.76). ... 

Li, Q.A., Ruckstuhl, T., and Seeger, S. 2004. Deep-UV laser-based fluorescence lifetime imaging microscopy of single molecules. J. Phys. Chem. B 108 8324. 

Detect the fluorescent-labeled protein using a laser-based fluorescent scanner. An experimental example is shown in Fig. 3 see Note 23). 

Fig. 3. Detection of a synthesized protein by fluorescent labeling. Cell-free protein synthesis was carried out with or without the use of mRNA transcribed from a linearized expression done containing the p-gaiactosidase gene, and the synthesized protein was labeled by FluoroTect. The translational reaction mixtures were resolved by 12.5% SDS-PAGE. Detection of labeled protein was performed using a laser-based fluorescent scanner (FX pro, Bio-Rad, Hercules, CA). Lanes 1 and 2 represent negative control (absence of mRNA) and p-galactosidase, respectively.

Fluorescent probes for microscopic evaluation of free intracellular Mg(II) should fulfil requirements such as adequate photochemical properties (excitation with laser-based instrumentation, high extinction coefficient and quantum yield, reduced interference from autofluorescence), low toxicity and low photochemical damage. Several Mg(II) microflu-orescent probes are in the market, for example, Mag-fura-2 (34a), Mag-indo-1 (35) and... 

Chemical Conversion Methods. Laser-Induced and Resonance Fluorescence of HO. Considerable effort has been applied to the measurement of HO in the stratosphere and troposphere. Ultraviolet fluorescence techniques based on lasers or resonance lamps have received a great deal of attention and study. Because HO concentrations are typically factors of one-tenth to one-hundredth those of H02 in the atmosphere, the difficulties associated with making HO measurements by using fluorescence [low signal-to-noise ratio, laser-generated HO, background fluorescence, etc. see the... 

The use of laser-induced fluorescence (LIF) for tropospheric HO and H02 measurements was reported by Hard and co-workers (108-110), who developed a fluorescence technique based on pumping the air sample into a low-pressure cell (FAGE) and exciting it with a copper vapor laser-pumped dye laser with a high repetition rate. Their H02 measurements were not made in conjunction with enough other supporting measurements to allow an accurate test of photochemical models from the results. 

The innovative thermostated separation system published by de Bokx et al. [17] represents an interesting example and comprises a capillary cross intersection for sample injection and a 100 pi fluorescence detector cell based on fiber optics. This apparatus shows basically all features that are required to perform automated fast and efficient electrophoretic separations and has been used to separate a mixture of laser dyes in 35 seconds with moderate efficiency. However, in order to keep all dead volumes at the junctions sufficiently small, the connections had to be done by tedious laser-based drilling of holes through the capillary walls. A similar approach to interconnect capillaries was described for a postcolumn derivatization reactor for CE [18], and many more inventive capillary coupling devices have been designed. 

The quantity and volume of samples required for impurity determination by CZE are very small probably less than 5 uL of volume is required for a well-designed injector, and only a few nanoliters (i.e., a few nanograms) are actually injected. However, it is experimentally simpler if that sample is present in a relatively concentrated solution, 0.05-2 mg/mL, when UV detection is being used. Our focus was not to achieve ultra-low detection limits such as might be required for trace level contaminants or for quantitation of trace levels of natural products. For those applications, the most common approach has been the use of a laser-based detector, preferably combined with a fluorescent label on the analyte. With this combination, extremely low limits of detection can be achieved (9, 22-25). 

In addition to the IR, Raman and LIBS methods previously discussed, a number of other laser-based methods for explosives detection have been developed over the years. The following section briefly describes the ultraviolet and visible (UV/vis) absorption spectra of EM and discusses the techniques of laser desorption (LD), PF with detection through resonance-enhanced multiphoton ionization (REMPI) or laser-induced fluorescence (LIF), photoacoustic spectroscopy (PAS), variations on the light ranging and detecting (LIDAR) method, and photoluminescence. Table 2 summarizes the LODs of several explosive-related compounds (ERC) and EM obtained by the techniques described in this section. 

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. 

The idea behind a spintronic biochip or biosensor is to replace traditionally used fluorescent markers by magnetic labels. Instead of detecting biomolecular recognition using expensive optical or laser-based... 

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