Research On Terahertz Spectroscopy Of The Basic Units Of Life

Terahertz(THz)wave is an electromagnetic wave with its frequencies from 0.1-10 THz that lies between infrared and microwave.With the gradual maturity of THz wave generation and detection technology,it has been widely used in communications,materials,national defense security,biomedicine and other fields.For biological macromolecules,low frequency stretching and bending vibrations between and within molecules,phonon vibrations of lattices and stretching and torsion vibrations of hydrogen bonds pertain to the primary reasons of generating high-level structure and motion.Hydrogen bonds,van der Waals forces,and skeletal vibrations between or within nucleic acids,proteins,sugars and lipids that reflect the biological functions of biological molecules fall in the THz range.Therefore,the THz spectroscopy of biomolecules has drawn great attention in recent years.THz time-domain spectroscopy(THz-TDS)is an effective coherent detection technique for deeply understanding the structures and functions of biomolecules.However,generally not full information in the whole THz range can be obtained due to the limited detection bandwidth(usually less than 5 THz)of the traditional THz TDS systems.The lack of THz spectral information in the high frequency band restricts the further development of THz technology in the biological field.In order to obtain more comprehensive spectral information of biomolecules in the THz range,the main research work includes following aspects:Firstly,the installation,debugging and optimization of the broadband THz time-domain spectral system(ZAP)were performed on the basis of the current equipments at the laboratory according to the generation and detection principle of broadband THz radiation.The ZAP system was tested and analyzed after optimized.The stable THz radiation with a high signal-to-noise ratio in the frequency range of 0.5-10 THz was obtained,providing broadband THz detection ability and stable,effective experimental facility for subsequent experiments.This broadband THz-TDS system breaks through the limitation of narrow detection range of traditional THz-TDS ones.Secondly,according to the method of optical parameters of samples extracted from THz time-domain spectrum and the output mode of data of ZAP,a program coded by Matlab was used to calculate the optical parameters of sample,including frequency spectrum,phase,refractive index and absorption coefficient etc.These parameters then was used to calculated the absorption spectra for biological molecules.Thirdly,THz time-domain spectra for base-pairs,Adenine(A),Guanine(G),Cytosine(C),Thymine(T)and Uracil(U),the conponents of genetic material DNA and RNA,were investigated systematically using the optimized ZAP system.Their THz absorption spectra in the 0.5-10 THz band were calculated with our Matlab code.Some new characteristic absorption peaks of these biomolecules are found firstly in the high frequency range of 5-10 THz.This work fill the gap for the lack of high frequency band information in previous research reports.The results indicate that these biomolecules have resonance responses in the whole THz spectrum,being the premise and basis for further research on biological effects of broadband THz waves.Finally,the results of the published reports on the THz spectrum of AGCTU using THz-TDS technology are summarized and compared with our work.The accuracy of the results are discussed.Our results would be helpful for the improvement for the THz “fingerprint” spectrum database of the biomolecules.