Scattering in Biomedical Infrared Spectroscopy

School of Chemical Engineering and Analytical Science, Manchester Interdisciplinary Biocentre (MIB), University of Manchester, 131 Princess Street, Manchester Ml 7DN, UK 

In the diagnostic application of synchrotron radiation Fourier transform IR (SR-FTIR) we are interested in measuring single cell spectra, or high resolution images of cells/tissue. The measured spectra are often distorted by scattering effects such that the biochemical information is rendered unreliable. This 

Infrared spectrum of a cultured isolated single cell from a prostate cancer (PC-3) cell line as measured with a synchrotron source. 

---

This article shows how the evanescent wave can be used with advantage for spectroscopic purposes in the field of biomedical engineering. Three types of spectroscopy can be done with the evanescent wave in the UV-VIS range of the spectrum (a) attenuated total reflection (ATR) spectroscopy, which is well known in the infrared (b) the excitation of Raman scattering with the evanescent wave and (c) the excitation of fluorescence with the evanescent wave. The first two types will be discussed in this article the third is discussed for example by Hirschfeld U) and more recently by Watkins and Robertson (2). But before going into details a historical review may be of some interest. 

For any vibrational mode, the relative intensities of Stokes and anti-Stokes scattering depend only on the temperature. Measurement of this ratio can be used for temperature measurement, although this application is not commonly encountered in pharmaceutical or biomedical applications. Raman scattering based on rotational transitions in the gas phase and low energy (near-infrared) electronic transitions in condensed phases can also be observed. These forms of Raman scattering are sometimes used by physical chemists. However, as a practical matter, to most scientists, Raman spectroscopy means and will continue to mean vibrational Raman spectroscopy. 

---