Research On Biomolecules Identification And Their Interactions Based On Terahertz Time-Domain Spectroscopy Technology

Terahertz(THz)radiation is in the frequency range of 0.1-10 THz of the electromagnetic spectrum,sandwiched between microwave and infrared,bridging the transition area of traditional electronics and photonics,As an important approach of spectral measurement technology,the terahertz time-domain spectroscopy(THz-TDS)technology exhibits a number of unique advantages,enabling direct extraction of absorption coefficient,refractive index,and complex dielectric permittivity in the terahertz band.THz photons have energies corresponding to excitations of vibrations,rotations,configurational and conformational changes of organic and biomolecules(such as DNA,RNA,protein,etc.),making THz spectroscopy a very effective tool for studying biomolecules and organic matter.THz-TDS provides a new perspective on further understanding of the structural properties of matter,especially biological matter(tissues,cells,and biomolecules).Based on the analysis and reference to previous research on THz-TDS,we attempted using THz-TDS technology to detect the three phases of matter,i.e.,solid-phase,liquid-phase,and liquid-phase combined with the metamaterials,and the measurement results are discussed,and argued in favor of the feasibility of terahertz technology in the accurate detection of such matter.This paper is supported by National 973 Program of China(Project No.2015CB755401),the Chinese Ministry of Science and Technology(Project No.2012BAK04B03),the Chongqing Science and Technology Commission(Project No.cstc2013yykfC00007).The main research contents are as:1)A detailed review and summary of the research status of the application of terahertz spectroscopy in study of biomolecules;Focuses on the research results associated with the use of THz-TDS technology for the detection of solid-phase samples,liquid-phase samples and the metamaterials combined with liquid-phase samples;In the following sections,the sample making process and experimental equipment used in the experiment are described.On this basis,the main research ideas and contents of this paper are put forward.2)The production process and cautions of different biomolecular samples are described in detail;The principle and system structure of terahertz time domain spectroscopy are introduced,and the theoretical basis and method of extracting material parameters are discussed;The principle and system structure of the transmissive THz-TDS technology and the theoretical basis and method of extracting material parameters are discussed in detail.3)Considering that some biomolecules have no distinctive absorption peaks,we used principal component analysis(PCA)to extract the main components of the spectral data of different biomolecule samples.Then,the support vector machine(GA-SVM)of the genetic algorithm and the grid search-SVM are compared and analyzed.The results show that GA-SVM is an efficient,parallel and integrated search algorithm that automatically controls the search process to determine the optimal solution adaptively.The algorithm produces accurate recognition results and converges well,even if the training samples are limited.The combination of THz-TDS technology and pattern recognition has the potential to identify different types of solid-phase biomolecules.4)Considering the problem that the traditional biomedical method will interfere with the fluorescent agent when detecting the interaction of liquid biomolecules,a method for label-free detection of biomolecular interaction using THz-TDS is proposed;THz spectroscopy was employed to detect the binding reaction of AER-? with the AER-?-specific antigen ERP-?.Compared with classical methods(ELISA and IHC),THz spectroscopy is fast,convenient and label-free,which can potentially avoid the interference of the fluorescent agent in the binding reaction,and better reflect the true physiological state of the antigen-antibody binding.The measurement results showed that the hydration shell was constantly present in the AER-?,and AER-? /ERP-? solutions,and played an important role in the THz absorption of these solutions.Specifically,the binding interaction of AER-? and ERP-? effectively caused the hydration shell to diminish gradually until it disappeared.This hitherto unreported phenomenon shows that THz spectroscopy can be used to detect the configurational change of protein caused by occupation and population of antibody/antigen binding sites.Finally,compared with traditional biomedical methods,it is proved that THz-TDS technology is feasible and reliable in detecting liquid biomolecular interactions.5)Some liquid-phase biomolecules that are not sensitive to the terahertz field response under normal conditions,a split-ring resonator(SRR)structure is proposed to enhance the local electromagnetic response of the terahertz field,thereby enhancing the terahertz spectrum.A solution for the detection sensitivity of liquid biomolecules.To achieve the detection of different liquid biomolecules.The SRR structure was designed and manufactured,and the actually manufactured SRR structure parameters agree well with the theoretical simulation.Four different fatty acids were distinguished from the real and imaginary parts of the transmission spectrum by using SRR combined with THz-TDS for four different fatty acids: oleic acid,linoleic acid,?-linolenic acid and ?-linolenic acid.We also used THz-TDS combined with SRR structure to measure the transmission mode of different concentrations of protein solution.From the experimental results,we could effectively differentiate the protein solution;and the frequency shift of the resnance peak was fitted with the protein concentration.The minimum detection concentration was 0.001 mg/ml.Then the Rabbit IgG proteins with different concentrations were fitted to the frequency offset,and the reasons for the different frequency shifts at different concentrations of protein were analyzed from the perspective of hydration kinetics.The terahertz transmission spectra of Rabbit IgG + anti-Rabbit IgG solution combination and Rabbit IgG + BSA solution combination based on the SRR structure were measured.By comparing the difference in the resonance frequency shift of resonance peaks,twe obtained that the SRR structure based on THz-TDS was able to determine the reaction of the two proteins.