Pathology by infrared and raman spectroscopy

The term pathology comes from the Greek words pathos (suffering, disease) and logos (reason) and refers to the study of the nature and cause of disease. While clear and concise, this straightforward definition belies the complexity of the discipline of pathology. A complete understanding of the nature and cause of disease requires an understanding of the nature and cause of disease requires an understanding of biochemistry at all levels of biological hierarchy, from basic structure at the molecular level to interactions between tissues and organs in the intact organism. Between these two extremes knowledge of the properties of macromolecular assemblies and of the biochemistry of cellular organelles, cells and tissues is required. Techniques currently employed in pathology range from those that have been used for hundreds of years by physiologists, anatomists and pathologists to study cell/tissue architecture and biochemistry (such as light microscopy) to more recent developments which probe structure and composition at the molecular and supramolecular level (electron microscopy, molecular biology techniques such as polymerase chain reaction). However, few of these techniques can be applied at each of the levels of organization mentioned above. Thus a detailed understanding of pathological processes can only be achieved by applying a wide variety of techniques to these highly complex systems. Biophysical, specifically spectroscopic, methods may hold the key to extracting information concerning biochemistry at a variety of levels. Spectroscopic techniques, i.e. techniques based upon the interaction of light with matter, have long been used to study biochemistry, both in vivo and ex vivo. Indeed the earliest diagnostic tool, physical examination may be thought of as a form of visible spectroscopy. More familiar applications of light in medicine include the use of UV-visible spectroscopy for determination of clinically important analytes, X-rays for examination of hard tissues and angiography and the use of radio waves in magnetic resonance imaging. While not yet accepted as a clinical tool, vibrational spectroscopy holds significant promise for analysis of pathological samples. Vibrational techniques can provide information on isolated biological materials, single cells, biological fluids or complex tissues. This information may pertain to nuclear material, membrane dynamics or connective tissue, to give only a few examples. Importantly, such varied information may be obtained in a single measurement from microscopic samples. Furthermore, spatial variations in tissues may also be assessed. Clearly, then, vibrational techniques hold promise in the study of the nature disease. Two vibrational techniques may be applied to pathological samples: infrared (IR) spectroscopy and Raman spectroscopy. Although these techniques are closely related, historical development of the two techniques, the type of information they provide when applied to tissues and cells and the instrumentation required is significantly different. While not intended to be a comprehensive overview of these differences, they will be discussed to allow the reader to place the discussion of current and future applications of the two techniques in context.Peer reviewed: YesNRC publication: Ye