Synchrotron FTIR microspectroscopy

Confocal Raman microspectroscopy is now yielding spectra at micrometer spatial (lateral) resolution, and can be carried out in situ (Figure 6). Diffusion profiles can also be mapped. The potential for FTIR microspectroscopy is also apparent, and results have been obtained that are superior to those from OTTLE cells, with simpler cell design, thanks to the use of microelectrodes. But the discrimination against solvent absorption is poor for in situ work it is hoped that higher intensity sources, such as synchrotron sources, in conjunction with PM-IR-RAS, can overcome this problem. 

E. Gazi, J. Dwyer, N. P. Lockyer, P. Gardner, J. Miyan, C. A. Hart, M. D. Brown and N. W. Clarke, Fixation Protocols for subcellular imaging using synchrotron based FTIR-microspectroscopy, Biopolymers, 2005, 77, 18 30. 

In general, the goal for synchrotron-based FTIR microspectroscopy is to deliver images at the diffraction limit. This usually means setting one (or both) of the microscope s apertures to define a region somewhat smaller than the diffraction limit for the respective objective. For convenience, we use d= XjNA to define this diffraction-limited dimension. This is consistent with the calculated Full Width at Half Maximum (FWHM) of the Schwarzschild diffraction pattern and is also confirmed by experimental resolution studies on test specimens (to be shown later in this section). 

Figure 11.4 Infrared spectrum of hamster peripheral nervous tissue in the spectral range from 4000-900 cm measured at a synchrotron source by FTIR microspectroscopy through a lOxlOpm aperture.

One of the strengths of FTIR spectroscopy is its diverse range of sampling techniques. Examples include attenuated total reflectance (ATR), diffuse reflectance (DRIFT), photoacoustic (PA), grazing angle, microspectroscopy and more specialised techniques such as synchrotron-radiation-based FTIR (SR-FTIR) microspectroscopy 11-12). The following section outlines ATR and SR-FTIR microspectroscopy in more detail and then provides specific applications of their use for the analysis of C. neoformans, S. favosa and L crassa. 

Synchrotron-Radiation-Based Infrared (SR-FTIR) Microspectroscopy... 

Using synchrotron transmission FTIR microspectroscopy as a rapid, direct and nondestructive analytical technique to reveal molecular microstructural-chemical features within tissue in grain barley. /. Agric. Food Chem., 52 (6),... 

The optical requirements for an IR microscope include (i) exact positioning of the sample (ii) spatial isolation of the sample from a larger matrix in the IR beam and (Hi) capability to function in both the visible and the infrared spectral regions. For infrared microspectrometry, a thermal emission source is generally used. Fourier transform spectrometers use interferometers as an effective means to resolve photon energies. Mercury cadmium telluride (MCT) detectors have the sensitivity and speed needed for FTIR spectrometers. The use of synchrotron radiation dramatically improves infrared microspectroscopy and has the power to analyse and map samples at high resolution. SR sources have transformed the IR microspectrometer into a true IR microprobe, providing IR spectra at the diffraction limit. Optics and performance of a /uF llR interfaced with SR were described [423]. Some 15 synchrotron beam lines are equipped with IR microscopes. 

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