ABSTRACT
Raman and infrared spectroscopy have provided molecular characterizations of complex assemblies spanning the chemical, physical, and biological sciences. Over the past forty years, the development of powerful vibrational microscopy techniques has evolved into the ability to reconstruct a sample’s image to allow the visualization of the spatial distribution of chemical components across a specific sample area. Images can be reconstructed from two basic instrumental approaches: in the first configuration, the image, employing a single detector, is assembled from specific, small spatial areas that are relatively coarsely spaced across the sample from which spectral information is acquired. These methods are typically termed point spectroscopic mapping. In the second configuration, spectroscopic information using multiple detectors is acquired over a portion of the observed region of interest defined by an optical image. These techniques are closer to conventional optical, bright-field imaging methods and involve either line scanning or the more recent wide-field, global imaging processes. Since the visualization is accompanied by appropriate magnification for examining a specimen’s microscopic structure, these spectroscopic image reconstruction techniques are also variously termed vibrational microscopy, vibrational imaging, or microspectroscopic imaging techniques.1 Since current instrumentation has advanced to the point where it is nearly as efficient to collect a spectroscopic imaging data set as it is to collect spectra at only several points within a sample of interest,2 we emphasize in this discussion an examination of the technology and applications of vibrational spectroscopic imaging involving spatially resolved spectral measurements across large sections of the optical field of view. The chapter is divided into two main sections, discussing in detail approaches in which spatially resolved Raman and infrared spectroscopic data sets are acquired.
