Biomedical applications of X-ray absorption and vibrational spectroscopic microscopies in obtaining structural information from complex systems

Vibrational spectroscopic mapping and imaging of tissues and cells

“…A number of recent reviews (Bailo and Deckert 2008;Bhargava 2007;Boskey and Mendelsohn 2005;Chan et alhave highlighted various aspects of vibrational spectroscopic mapping and the imaging of cells and tissues, as well as the use of complementary microscopic imaging/ mapping (Aitken et al 2009;Eichert et al 2007;Miller et al 2007). This review will discuss the techniques used in obtaining vibrational spectroscopic images and maps of cells and tissues, and the types of biochemical information that are available through the use of these techniques.…”

“…The energy of mid-IR light provides a molecule with sufficient energy to vibrate but not enough energy to result in ionization or to break bonds and, consequently, there is no photodamage to the sample; local heating has been found to occur when using a synchrotron source, but it was reported to be too small (0.5°C) to be a significant problem (Martin et al 2001). This enables other mapping/imaging spectroscopies to be performed on the same sample after IR imaging or mapping (Aitken et al 2009). Signal (band) intensities vary with the concentration and the nature of functional groups in the molecule (primary structure) and with its conformation (secondary structure).…”

“…The conventional source in benchtop instruments is a globar source, which produces an intense IR radiation over the entire mid-IR range. A synchrotron source relies on collecting the IR radiation component of synchrotron radiation that is emitted when the trajectory of an intense beam of electrons traveling close to the speed of light is changed by a bending magnet in the synchrotron ring (Aitken et al 2009;Carr et al 1995;Miller et al 2007). Both sources produce a comparable number of IR photons per unit of time, but radiation from the globar source is widely dispersed, while the synchrotron source is highly focused.…”

“…This arises from the small synchrotron IR spot size, which means that only the inner detectors of the array have sufficient responses to be used in imaging. As discussed previously (Aitken et al 2009), specialist array detectors have been designed that achieve an effective geometric pixel size of 0.54×0.54 μm 2 , compared to the 6.25×6.25 μm 2 pixels that are the best case scenario for a globar. Such oversampling of the IR bandwidth results in an improvement in the deconvolution algorithms and, hence, the quality of the diffraction-limited images (Nasse et al 2007), leading to rapid measurements of highresolution maps of cells and tissues.…”

“…For example, Raman microprobe fibre optics have been combined with many other techniques (Aitken et al 2009;Williams et al 2003) including AFM (Biju et al 2007;Eronen et al 2009), microdiffraction (Davies et al 2009) and scanning electron microscopy (SEM), which is interfaced with the Raman spectrometer via a structural chemical analyzer allowing elemental and chemical information to be obtained from the same area of the same sample (Williams et al 2003).…”