Detection And Analysis Of Small Bio-molecules On Terahertz Time Domain Spectroscopy

Terahertz(THz) radiation lies in the frequency gap between the infrared and microwaves, which typically referred to as the frequencies from 100 GHz to 10 THz. It many unique properties and at present it is regarded as an important inter-discipline subject. THz waves have gained immense importance due to their applications in non-intrusive package inspection, medical diagnosis, ultra-high speed telecommunications as well as understanding the characteristics of molecules and biological systems. The bands in the THz region may be related to various modes.Hydrogen bonds, van der Waar force, rotation of dipole, low-frequency vibrations of lattices and other modes may be related to the bands in the THz region. Many biomolecules show spectral signatures in the THz range. In general, THz radiation is harmless to biomolecules, and the special functions of THz signals on water,biomolecules and nonpolar compounds present an opportunity to use terahertz detection technology in the area of biomedicine and pharmacy.The THz absorption spectra were recorded on the THz time domain device Teraview TPS 3000 in our lab, based on photoconductive switches for generation and detection. In this paper, the absorption spectra of THz range of two kinds of phenylthiourea derivatives(4-methylthiocarbanilide and 1-(2-hydroxyethyl)-1-methyl-3-phenylthiourea) and four kinds of para-substitued anilines(p-chloroaniline, p-toluidine,p-nitroaniline, p-methoxyaniline) are researched by using terahertz time-domain spectroscopy(THz-TDS).The results show that the biomolecules have fingerprints in the region of 0.1–3 THz(3-100 cm-1). According to the quantum chemistry calculation results by GAUSSIAN09, the bands in THz region mainly consist of movement of whole molecular skeleton. According to the crystal files in CCDC, we could observe the crystal position and category of different short contacts directly. These different fingerprints are attributed to molecular conformation, so absorption spectra of THz range could distinguish these samples.In the paper, we have tried to optimize the isolate molecule model and utilizing the two molecules model to simulate vibrational modes. The results are more consistent to experimental data and have the similar variation tendency, which are significant for simulations and experiments. In addition, in order to simplify the processes of THz-TDScalculations, we have design a Graphical User Interface(GUI) in MATLAB. It could be more convenient and effective to handle the data processing and comparison and benefit for further works.