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Research in Biomedical Optics

Raman Spectroscopy

Raman effect occurs when some of the energy from the incident light is transferred to the interacting sample, raising the molecules from their ground state to an excited vibrational (or rotational) state.  The strength of this coupling is proportional to the polarizability of the molecules, and the inelastically scattered light emerges with less energy than with which it entered.  Since each type of molecule has a unique bonding structure, the Raman scattered light exhibits a unique pattern of energy shifts in the spectrum for each type of molecule.  Hence, by analyzing the spectrum of the Raman scattered light, information about the chemical composition of the target material can be extracted.  This technique is used in biomedical Raman spectroscopy to non-invasively estimate the biochemical composition of the target tissue.
In order to estimate the tissue composition, the major Raman scatterers are first identified for the target tissue of interest.  Separately obtained individual Raman spectra of these basic components form the tissue model basis spectra (Figure 1(A)), which are linearly combined to fit with the Raman spectrum of the target tissue (Figure 1(B, C)).  Tissue compositional information obtained in such a manner helps to identify pathological tissues for disease diagnosis.[1]  With accurate calibration with samples of known concentrations, similar methods can also be used in quantitatively measuring blood analyte concentrations.[2] 

Figure 1. Characterization of arterial tissue composition by Raman spectroscopy

Recent Publications

  1. H. P. Buschman, G. Deinum, J. T. Motz, M. Fitzmaurice, J. R. Kramer, A. van der Laarse, A. V. Bruschke, and M. S. Feld, “Raman microspectroscopy of human coronary atherosclerosis: Biochemical assessment of cellular and extracellular morphologic structures in situ,” Cardiovascular Pathology 10(2): 69–82 (2001).
  2. A. M. K. Enejder, T.-W. Koo, J. Oh, M. Hunter, S. Sasic, G. L. Horowitz, M. S. Feld, “Blood analysis by Raman spectroscopy” Optics Letters 27, 2004-2006 ( 2002).