Light probe

Using a visible light probe NSOM is the eadiest of the probe scopes, at least in conception, and is another apparent exception to the diffraction-liinited resolution rule, in that NSOM illuminates an object with a beam of visible light smaller than the diffraction limit. The resolution then is limited only by the size of that beam. To achieve this, light issuing from a very tiny aperture at the end of a glass capillary scans a very near sample. The tip must be located on the order of X/2 from that surface. Resolution in the range of 10—20 nm has been achieved (31). 

Nye, J. O. and R. S. Brodkey (1967a). Light probe for measurement of turbulent concentration fluctuations. Review of Scientific Instrumentation 38, 26-28. 

Fig. 3. Pump-deplete-probe spectroscopy on lycopene in hexane, a) Experimental setup After excitation and depletion of Car S2 with a delay of r=50fs, a white-light probe pulse at delay tprob<.=2ps measures the transient absorption spectrum, b) Spectra without (solid curve) and with depletion pulse (dotted) and their difference (shaded area). Only the Car Si state is depleted the ground state bleach (S0-S2) and positive absorption feature on its low energy side (hotSo-S2) are unaffected.

Relatively simple optical experimental techniques to study noncohesive particulate flow have also been developed, such as the polarized light probe system by Allersma (42,43). With this technique, the principal stress distribution and displacement of photoelastic granular material flowing in two-dimensional hoppers, with and without obstructions (distribution bars), can be obtained, as shown in Fig. 4.18. 

A flnorescent-labeUed probe, which will emit visible light when Ulnminated with nltraviolet (UV) light. Probes can be made to flnoresce with different colonrs. 

Protein-lipid interactions and particularly peptide-lipid interactions have been studied in supported bilayers by attenuated total reflection (ATR) FTIR spectroscopy. A slightly dated, but still valid comprehensive review on this method applied to supported bilayers has been published (20). Because IR light probes the vibrational properties of different classes of covalent bonds, this method is useful to examine lipids, peptides, and interactions between the two in the same sample. The most common parameter for assessing lipid structure and order is to study the stretching vibrations of the lipid acyl chains, for example as a function of peptide concentration or temperature. Such studies have lead to the conclusion that fusion peptides from viruses increase the lipid chain order of fluid phase bilayers and that... 

It is important that the chosen fluorescent dyes are compatible with the scanner excitation wavelengths. Most scanners excite at 532 nm and 635 nm, making Cy3 and Cy5 (Amersham or NEN) compatible. Either dUTP- or dCTP-labeled nucleotides can be used, with the corresponding unlabeled nucleotide concentration reduced. Fluorescent dyes are photosensitive, so measures should be taken to minimize their exposure to light. Probe-labeling reactions, hybridizations, and so forth should be foil-wrapped or performed in light-proof containers wherever possible. 

Various techniques have been developed in recent years that are sensitive enough to allow a quantitative evaluation of the optical properties of these ultrathin coatings (see Swalen [45]). One group of techniques uses evanescent waves as highly specific sensitive interfacial light probes (see Knoll... 

The light source was a 1 KW Oriel Solar Simulator equipped with AMO filters. Light intensities were measured by a Karl Lambrecht calibrated light probe. The unattenuated power flux delivered by the System was 208 mW/cm. Incident light intensity was varied using neutral density filters. The light source for action spectra measurements consisted of a 150 W Xe lamp and a 14 meter Jarrel Ash monochromator. The action spectra of the cell was measured as described previously (7). 

Watarai and coworkers employed time-resolved spectroscopy to monitor the excited state lifetime of porphyrin species adsorbed at the toluene/water interface [37, 42]. Illumination with a white light probe and monochromatic pulse excitation in TIR revealed that the porphyrin H2TMPyP" exhibits a triplet state lifetime significantly shorter at the interface than in the bulk aqueous phase [42]. On the other hand, Doung et al. reported under similar experimental conditions (only pulse excitation in TIR) that the lifetime of H2TMPyP" only... 

Depth profiling is also a possibility using the ATR technique (a.21) and probed depth (i.e., how deep in the sample the light probes) varies as... 

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