Page 123 - Vibrational Spectroscopic Imaging for Biomedical Applications

CHAPTER 4

Evanescent Wave Imaging

Heather J. Gulley-Stahl, André J. Sommer
Molecular Microspectroscopy Laboratory
Department of Chemistry and Biochemistry
Miami University
Oxford, Ohio, USA

Andrew P. Evan

Department of Anatomy
Indiana University School of Medicine
Indianapolis, Indiana, USA

4.1 Introduction
Optical microscopy has been employed for well over 344 years to study
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tissue specimens at the cellular level. The optical microscope aids the
pathologist in this task by permitting the analysis of spatial domains as
small as 300 nm (0.3 μm). In diagnosing a disease, the pathologist looks
for structural changes in the cells or tissue. Alternatively, one can look for
chemical agents that enhance the contrast for a given structure or signal
the presence of a disease. This latter method of detection has been
employed for well over 298 years by using dyes or stains that are specific
2
for a disease state or chemical variant associated with the disease. Sev-
eral problems associated with histopathology stem from the fact that
there may not be a stain specific for the disease. In addition, the staining
procedure usually involves multiple steps during which the material of
interest may be lost or destroyed. In an effort to circumvent these prob-
lems, infrared methods of detection have been employed to gain similar
information. Here the chemical which signals a disease is detected directly
and all that is required is the preparation of a thin tissue section.However,
infrared wavelengths are an order of magnitude longer than visible wave-
lengths so the spatial domains accessible using this method are typically
an order of magnitude larger (~3 μm). To address this short-coming, infra-
red microspectroscopists have employed immersion methods commonly

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