Research On Terahertz Polarization Sensing Technology For Biochemical Substances Based On Metasurface

With the breakthrough of Terahertz（THz）radiation source and detection technology,and the maturity of various THz functional devices,THz technology has achieved rapid development in recent years,showing its great superiority and broad application prospects in the research fields of wireless communication,medical imaging,security inspection,and biological detection.In particular,due to its fingerprint spectral specificity,high signal-to-noise ratio and low radiation energy,THz wave has unique advantages of real-time,no label,non-contact and non-ionization in the sensing of biochemical substances.However,the existing THz sensing and detection methods mainly obtain the amplitude and phase information of THz wave after interaction with the sample.The polarization,chirality and other information have not been fully utilized,and many biochemical material structure information related to polarization and chirality cannot be obtained.In addition,the traditional THz refractive index sensing method based on the shift of the THz metasurface resonant frequency due to the refractive index change of the sample also faces the difficulties of strong water absorption and lack of specificity.Therefore,it is urgent to develop new THz biochemical sensing methods and systems in order to break through the development bottleneck of the existing THz biochemical sensing technology.In this thesis,the basic theory,research status and development trends of THz spectroscopy and sensing technology are summarized systematically.In view of the key scientific and technical problems existing in THz biochemical sensing technology,a THz polarization sensing technology based on reflective THz time-domain polarization spectroscopy system and polarization sensitive matasurface is proposed,which reduces the influence of water absorption,improves the integrity and detection specificity of information acquisition,and the detection accuracy and sensitivity of the sensing system are also improved.According to the requirements of different sample and detection environment,different polarization sensitive metasurface sensors are designed.The polarization sensing detection of chiral amino acid solution,protein and their structural changes,and number changes of cancer cells under the action of proliferation inhibitory drug are studied.The main research results and innovations are as follows:1.Research on the chiral sensing of amino acid solutions.A novel sensing method based on THz reflective time domain polarization spectroscopy（RTDPS）system and single-layer spiral metasurface sensor was proposed,and three amino acid aqueous solution and their chiral enantiomers（DL-proline,DL-alanine and DL-tyrosine）were tested.Compared with the traditional THz refractive index sensing method,the sensitivity and detection accuracy of chiral sensing have been significantly improved.The sensing accuracy of different amino acid samples reaches the order of 10^-5～10^-4 g/m L.In addition,the D-and L-chiral enantiomers of the same concentration can be distinguished by the significant difference in the polarization states at the characteristic frequencies,and the minimum concentration that can distinguish the difference between the chiral enantiomers can reach 10^-5 g/m L.The sensing system and the characterization method are not only applicable to amino acids,but also applicable to other biochemical solution samples with chiral molecular structures.2.Research on the polarization sensing of protein solution thermal denaturation process.A flexible twisted dual-layer metasurface sensor was designed and prepared,and the reflective THz time-domain polarization spectroscopy was used to study the temperature-dependent denaturation process of three protein（bovine serum albumin,whey protein and ovalbumin）aqueous solutions.The experimental results show that if the degree of protein denaturation is described as percentage,the sensing sensitivity of the sensing system can reach 6.30 d B/%,and the detection accuracy can reach0.77%.For the concentration sensing of protein solution,the sensing sensitivity and detection accuracy reached 52.9 d B·m L/g and 3.6·10^-5 g/m L,respectively.In addition,the difference between circular polarization spectra can be used to distinguish different protein types.3.Research on the polarization sensing of protein solution proteolysis process.The strong polarization response of the curved chiral double-layer metasurface sensor was used to realize the high-sensitivity sensing of bovine serum proteolysis under the action of papain.The experimental results show that under the action of different doses of papain,the THz polarization characteristic spectra of bovine serum albumin solutions are significantly different,and the sensitivity of frequency shift,peak intensity and polarization angle change reache 10⁶ GHz·m L/mol and 10⁶ d B·m L/mol,10⁶°·m L/mol,respectively.According to the sensing result of the hydrolysate,the concentration sensing of papain can be realized,and the detection accuracy can reach the order of nmol/ml.4.Research on the polarization sensing of cancer cell proliferation process.The silicon dielectric metagrating was used as a sensor,by generating and detecting the THz chiral polarization state,the circular dichroism sensing spectra was used to realize the quantitative detection and qualitative identification of the number and types of living cells in the culture medium.Three kinds of hepatocellular carcinoma cells（Hep G2,Huh7 and H7402）under the proliferation inhibition effect of aspirin were tested.The experimental results show that the detection sensitivities of spectral peak intensity changes and frequency shifts reached 3.44 d B·m L/10⁶ cells and 5.88GHz·m L/10⁶ cells,respectively.And the THz detection accuracy of cell number in culture medium environment was improved to the order of 10⁴ cells/ml.