Infrared Microspectroscopy of Human Tissue

Infrared spectroscopy is a convenient tool for determining the molecular conformations of proteins, lipids, and nucleic acids, as well as for identifying unknown chemical compounds. Previously, we have shown that infrared spectroscopy may be used to characterize the conformation of an abnormal protein found in pathologic specimens of medullary carcinoma of the thyroid. The technique described in that paper is of limited general utility, however, because it requires that the abnormal protein deposit constitute the vast majority of the tissue specimen examined by infrared spectroscopy. In addition, it requires that the specimen be mounted on a relatively expensive CaF2 crystal. Since it is customary in diagnostic pathology to retain such mounted specimens in perpetuity, a new crystal would be required for each specimen, resulting in relatively high sample preparation costs. The recent availability of high-optical-quality infrared microscopes eliminates the requirement that the abnormal material of interest constitute most of the specimen to be examined. In this note we describe a method for preparing samples which drastically reduces the cost of preparing a permanent specimen while, at the same time, making it somewhat easier to acquire optimal spectra.