PROBING THE METROLOGICAL USES OF RAMAN SPECTROSCOPY FOR STRUCTURE AND CONCENTRATION DETERMINATION

 

Rachel M. Stephenson1, Ashwinkumar Bhirde2, Xiaoyuan Chen2, Yihua Liu3, Liang Yueh Ou Yang3, Thomas P. Moffat3, Angela R. Hight Walker1

 

1National Institute for Standards and Technology, Optical Technology Division, Gaithersburg, MD 20899

2National Institute for Biomedical Imaging and Bioengineering, Laboratory of Molecular Imaging and Nanomedicine, Bethesda, MD 20892

3National Institute for Standards and Technology, Metallurgy Division, Gaithersburg, MD 20899

 

Raman spectroscopy is a powerful technique that reports on the vibrational modes of a sample, which in turn can be used to identify the sample.  Advantages of Raman spectroscopy include that it is a sensitive, non-destructive technique, and that the samples can vary over a wide range of conditions, including phase and temperature.  A desirable output from Raman spectroscopy is the translation of the spectroscopic signatures into absolute information such as molecular structure or concentration, however the method for doing this is often sample dependent.  Here, we present Raman spectroscopic data for three distinct systems, each which showcases a different aspect of the versatility of the spectroscopy, as well as different challenges towards absolute characteristics.  First, the effect of sample condition on structural conformation is investigated in trialanine, used here as a simple protein-mimetic system.  The visible Raman spectroscopic signatures of trialanine as a crystal, a solid pellet, and in solution (highly ordered to disordered) are compared.  In the second study, the uptake of DNA wrapped single-wall carbon nanotubes (SWCNTs), intended for use as drug delivery vehicles, is studied as a function of tube length and dosage.  A concentration calibration curve was created to determine the amount in the tissue samples.  Finally, surface-enhanced Raman spectroscopy (SERS) is used to study the potential dependent binding of small molecules to a copper surface.  As the potential is changed, different molecular signatures can be identified, highlighting the different surface chemistries.