Fingerprint-Region and Low-Frequency Raman Spectroscopy of Biomolecules

Abstract

Raman micro-spectroscopy is a powerful tool for biological studies. Low frequency (LF) Raman spectroscopy is useful for investigating the structure of molecular crystals. Intermolecular interactions and phonon resonances determine the LF-Raman modes. One possible application is to use LF-Raman mapping to differentiate facets of amino acid crystals. By changing the polarization of the incident photons, the stretching direction of hydrogen bonds can be studied and provide useful information of its crystal structure. In addition, Raman spectra of amino-acid solutions help to interpret spectra of other complex biomolecules, such as proteins. Principal component analysis (PCA) is a method that allows to deal with a large set of Raman data (both LF and fingerprint-region) and sort spectra by their subtle similarities and differences. In studying amino acids and proteins, a PCA loading plot is useful in evaluating correlations between the Raman spectra of crystals and aqueous solutions. Furthermore, by combining Raman spectroscopy with PCA we achieve efficient separation of distinct categories of biological samples, such as for example bacterial biofilms.