Single Molecule Spectroscopy Studies to Characterize Nanomaterials
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The optical detection of single molecules in the condensed phase was first demonstrated just over a decade ago by Moerner and Kador, Orrit and Bernard, and Shera et al. Since that time, single molecule spectroscopy has developed into a valuable tool for probing nanoscale heterogeneity in a wide variety of materials. For such studies, carefully selected dye molecules are doped into samples of interest at low concentrations. The individual molecules are then located and probed one at a time. Their signals are isolated from each other by spectral selection at cryogenic temperatures, and/or by spatial selection in an optical microscope. Detailed information on the time dependence, wavelength dependence, and polarization dependence of the excitation and emission processes can be obtained. Numerous spectroscopic parameters associated with the excitation and emission events in dye molecules are highly sensitive to the local environment in which each molecule resides. Therefore single molecule spectroscopy can be used as a direct means to assess the chemical and physical properties of the local environments found in almost any sample. The methods associated with the collection and interpretation of optical single molecule spectroscopic data for the purposes of understanding the environmental properties of nanostructured materials is the primary focus of this article.