| Chiral recognition is of great significance in the study of the origin of life,drug detection,disease diagnosis and environmental protection.The traditional method for chiral recognition is mainly in the optical band,which has some shortcomings such as long detection time,expensive instrument,dependence on chemical synthesis and reaction technology,and not suitable for the detection of active chiral molecules.Terahertz(THz)waves refer to electromagnetic waves with frequency ranging from 0.1 to 10 THz.Compared with the optical band,the radiation photon energy of terahertz radiation is very low,which will not cause biological ionization when performing biological detection.On the other hand,the terahertz electromagnetic spectrum corresponds to the rotational and vibrational energy levels of organics and biomolecules.The identification of chiral biomolecules in the terahertz band is expected to become an effective method to understand the activity of biomolecules and the interaction between molecules.However,in the terahertz band,many chiral biomolecules are difficult to be directly identified by using terahertz time domain spectroscopy technology without obvious characteristic spectra.Metasurface is a kind of artificially periodic structure that can enhance the local electromagnetic resonance response,realize sub-wavelength resolution,and greatly improve the resolution and sensitivity of sensors through reasonable design.The existing research on terahertz band metasurface sensors is usually aimed at detecting different types of biomolecules or different concentrations of the same biomolecule,and the identification of chiral biomolecules and enantiomers is very rare.Therefore,two methods are used to detect chiral biomolecules in this paper.One is based on the developed terahertz metasurface sensor to explore the physical mechanism of the interaction between chiral media and sensors,and to achieve the identification of different chiral biomolecules.The other is to establish a terahertz spectrum library,and combine three artificial intelligence algorithms to realize the identification of terahertz chiral biomolecules.This paper is based on the National Natural Science Foundation project "Research on terahertz metasurface sensors and their interaction mechanisms for chiral molecule detection"(Number:62175016),which belongs to the interdisciplinary field of terahertz technology and biological sciences,and meets the significant application requirements in the field of national life sciences and chiral drug detection.The main work and innovations of the paper are as follows:1.Extraction and experimental verification of chiral parameters in the terahertz band.The physical model of chiral biomolecules is established,and the chiral parameters corresponding to the circular polarized waves are extracted based on Maxwell equation.The circular polarized transmission spectra of the solid chiral ibuprofen and the liquid lactic acid are obtained through the experiment,and the chiral parameters κ of(R)-(-)-ibuprofen,(S)-(+)-ibuprofen,L-lactic acid and D-lactic acid are extracted based on the parameter extraction formula.Then the chiral parameters are used to study the mutual coupling between the chiral mediums and the terahertz metasurface sensors in COMSOL software.The simulation results are basically consistent with the experimental results,which verify the reliability of chiral parameter extraction.2.Terahertz metasurface sensor for the detection of glucose enantiomers and their specificity.A metasurface sensor with an adjacent opening electromagnetically induced transparent structure is developed,which can realize the quantitative detection of D-glucose according to the frequency shift.The sensitivity of the sensor can reach 0.9 THz/(mol/L)with the detection limit of 18mg/dL,which achieves the lowest detection limit in the terahertz band.A "cross" shaped terahertz metasurface sensor is developed to detect the chirality of glucose for the first time.The sensitivity of the sensor to D-glucose and L-glucose are 0.7 THz/(mol/L)and 0.4 THz/(mol/L),respectively.In addition,the sensor combined with principal component analysis to realize the specificity of D-lactose,Dfructose and D-glucose detection.3.Terahertz polarization-sensitive metasurface sensor for the detection of chiral ibuprofen in solid and liquid phases.A THz metasurface sensor is developed to achieve qualitative and quantitative detection of ibuprofen in solid and liquid phases by using different responses to polarization waves.For solid samples,the detection of chiral ibuprofen samples can be achieved in TM mode with the sensitivity for(R)-(-)ibuprofen and(S)-(+)-ibuprofen are 23.75 THz/RIU and 28.57 THz/RIU,respectively.For liquid phase samples,the sensitivity of ibuprofen enantiomers is different under different polarization modes.The sensitivity of(R)-(-)-ibuprofen in the TM and TE polarization modes is 1.5 THz/(mg/mL)and 2.1 THz/(mg/mL),respectively,and for(S)-(+)ibuprofen,is 1.7 THz/(mg/L)and 1.8THz/(mg/L),respectively.Based on the chiral parameters extracted of the chiral ibuprofen from circularly polarized wave transmission coefficient,the working principle of sensor recognition of chiral ibuprofen is verified by theoretical analysis combined with experiments.4.Achiral and chiral terahertz metasurface sensors for the detection of chiral lactic acid.The frequency shift of the transmission spectrum of the achiral metasurface sensor is used to realize the quantitative detection of different concentrations of the same chiral lactic acid and the qualitative recognition of different chiral lactic acid with same concentrations.The detection limit can reach 0.01μg/mL,and the sensing sensitivity of L-lactic acid,D-lactic acid and DL-lactic acid are 0.28 THz/(mg/mL),0.07 THz/(mg/mL)and 0.13 THz/(mg/mL),respectively.The frequency shift of the circular dichroic spectrum of the chiral metasurface sensor is used for the qualitative and quantitative detection of lactic acid.The sensitivity of the sensor for L-lactic acid,D-lactic acid and DL-lactic acid are 1.1 GHz/(mg/mL),0.9 GHz/(mg/mL)and 1 GHz/(mg/mL),respectively.Based on the extracted chiral parameters of lactic acid,theoretical analysis and experiment are combined to verify the working principle of chiral and achiral sensors to recognize the chiral lactic acids.5.Terahertz intelligent recognition of chiral amino acids based on multiple modes.The terahertz characteristic spectrum library of 20 amino acid enantiomers was established through experimental tests,and the multi-modal artificial intelligence algorithms(principal component analysis-random forest algorithm,particle swarm optimization-support vector machine algorithm and principal component analysis-particle swarm optimization-support vector machine algorithm)are used to identify the chiral amino acids from multiple dimensions.The advantages and disadvantages of three artificial intelligence algorithms in recognition accuracy and computational efficiency are compared.Principal component analysis-particle swarm optimization-support vector machine algorithm can effectively improve the computational efficiency on the premise of guaranteeing the recognition accuracy.The recognition accuracy and efficiency of the identification of amino acid enantiomers by the two methods of classifying first and then identifying chirality and direct identification of chirality are compared,and the identification rate of the direct identification method is higher with the recognition rate can reach more than 99%.In addition,a universal visual terahertz intelligent recognition system for amino acid enantiomers is developed,which can intuitively give recognition and analysis results. |
PDF Full Text Request