Terahertz Fourier transform characterization of biological materials in solid and liquid phases

Significant progress has been achieved during the last several years relating to experimental and theoretical aspects of Terahertz (or Sub-millimeter wave) Fourier transform spectroscopy of biological macromolecules. Multiple resonance due to low frequency vibrational modes within biological macromolecules have been unambiguously demonstrated. However till now only solid films of bio-materials have been used for experimental characterization in this spectral range since it was common opinion that high water absorption will prevent from receiving the information on bio-molecules in a liquid phase. At the same time, all biological function of DNA and proteins take place in water solutions. In this work spectra of DNA samples and proteins have been measured in liquid phase (gel) in a spectral range 10-25 cm-1 and compared with spectra obtained from solid films. The results demonstrate that there is almost no interference between spectral features of material in test and water background except for the band around 18.6 cm-1. Much higher level of sensitivity and higher sharpness of vibrational modes in liquid environment in comparison with solid phase is observed with the width of spectral lines 0.3-0.5 cm-1. Gel samples demonstrate effects of polarization. The ability of THz spectroscopy to characterize samples in liquid phase could be very important since it permits to look at DNA interactions, protein-protein interactions in real (wet) samples. One demonstrated example of practical importance is the ability to discriminate between spectral patterns for native and denaturated DNA.