Research On Measurement Technology Of Bio-molecules Based On Terahertz Time-domain Spectroscopy

Being situated between infrared light and microwave radiation, terahertz wave is loosely defined by the frequency range of 0.1 to 20 THz. It is a special region that occupyies the transitional zone from electronics to phtonics, and theoretically it is a crossing area of macro classic and micro quantum. Therefore, terahertz radiation has high value both in academic and application. Terahertz time domain spectroscopy (THz-TDS) is a new technique that applied to spectroscopic measurement based on ultrafast femtosecond laser. THz-TDS can analyse the components and the tiny change in the structure of the materials based on the distinct absorbtance of THz radiation. So, it is widely used to the study the optical characteristics of chemical and biological molecules in the terahertz region in recent years. Aided by quantum chemical calculation, THz-TDS technology has been used to measure and analyse the THz spectra of some typical saccharides and amino acids found in nature. The results show that the far-infrared absorption features of biomolecules are highly sensitive to the structure and spatial arrangement of molecules, and then THz-TDS can be used for discrimination of compounds which have minor differences.The major contributions in this dissertation are as follows:(1) THz time domain spectroscopy has been used to study the far-infrared spectroscopic characteristics of 14 typical saccharide biomolecules in the Nitrogen surroundings at room temperature. Frequency domain spectra and well-resolved absorption spectra were obtained between 0.2-2.6THz. The experimental results shows that the THz absorption spectra of 14 saccharide biomolecules have distinct characteristics in THz region, which can be used as the fingerprint spectra and discriminate the saccharide biomolecules which have minor differences. This study provide experimental results for the construction of fingerprint spectra database of the saccharide biomolecules and for deeply understanding of the conformation and configuration of the the saccharide biomolecules.(2) In order to interpret the problem of accordance and difference among the THz absorption spectra, a research method combined by the experiments of crystalline and amorphous glucose and quantum chemical simulations is proposed. The results show that the identical resonance in 2.09THz is originated from the collective vibrational modes triggered by the torsional vibrations of the pyran ringsin hexoses; and the other characteristic resonances of the hexoses is originated from the intermolecular collective modes mediated by hydrogen bonding network of the crystalline structure.(3) A comparative experiment of disaccharides and the hexoses which are the components of the disaccharides is proposed. The experimental results show that the spectra of disaccharide have more characteristic resonances in the same THz region. According to the differences of the structures between monosaccharide and disaccharide, the relations between the characteristic spectra of disaccharides and their collective vibrational modes originated from the inter- and intra-molecules are discussed.(4) A novel measurement method of chiral medicine based on THz time domain spectroscopy is proposed and the theoretical mechanism of the method is deeply analysed. Taking glutamic acid and phenylalanine as examples, the THz-TDS is used to measure the enantiomers and their racemic compounds of the two amino acids. The results show that the spectra between the enantiomers and their racemic compounds have distinct differences. The differences come from the different crystal lattice vibrational modes and the different intermolecular interactions originated from the crystalline structure. Intra-molecular vibrational mods have few contributions to the spectra due to the tiny differences of molecular structure. This research provided a fast, efficient, uncontact and nondestructive measurement method for inspection of the food safety and chiral medicine safety.(5) A combined method of THz time domain spectroscopy , fourier transform infrared spectroscopy and the quantum chemical simulation is proposed. The vibrational modes of β -D-pyrangalactose are discussed in the wider frequency region. Aided by Gauss View3.0 software and the theoretical results, the vibrational modes between 1.5 and 19.5THz have been assigned. The results show that the theoretical calculations are in good agreement with the experimental data, and the observed resonances in the high frquency above 6THz are originating from distinct intra-molecular vibrational modes while observed resonances in the low frequency below 6THz are dominated by vibrations of hydrogen bonds between the molecules or phonon modes.