Mid infrared microspectroscopic mapping and imaging: a bio-analytical tool for spatially and chemically resolved tissue characterization and evaluation of drug permeation within tissues.

The combination of the two classical biophysical methods, microscopy and infrared spectroscopy, has led to the development of a potent analytical technology termed infrared microspectroscopy. It combines high lateral resolution as obtained by microscopy and the chemical identification of the sample components by infrared spectroscopy. The two approaches mainly utilized in microspectroscopy are the mapping and the imaging techniques, which are introduced and presented. Especially, since the development of so called focal plane array detectors, which are implemented in the imaging methods (microspectroscopic imaging) has become a promising bio-analytical tool for ultrastructural medical diagnostics, due to the fact that the time required for analyzing a sample has been reduced dramatically and the lateral resolution improved to approximately 4 microm. Mid infrared microscopy allows a direct access to spatially resolved molecular and structural information of the analyzed area. The image contrast is generated on the basis of the tissue's intrinsic biochemical composition. The current investigation shows how mid infrared microspectroscopic mapping and imaging is used for the bio-analytical characterization and identification of specific molecular components of a tissue sample at high lateral resolution of a few microns (approaching the mid infrared diffraction limit). Furthermore, the potential of these methods for monitoring the penetration and distribution of drugs within biological tissues are presented. Due to the fact, that mid infrared microspectroscopy is a noninvasive, nondestructive technique for the analyzed sample, requiring no complicated and time consuming staining procedures, it is a convenient method for histological and pathological investigations, allowing the generation of a huge amount of biochemical information not yet available with other nonvibrational techniques. The strength of the presented microscopic technique is the fact that the infrared images are directly comparable to outcomes of classical histological staining procedures and can be interpreted by nonspectroscopists.