A TCD spectral measurement biosensor based on linearly polarized incident light and a testing method

Abstract

The application discloses a TCD spectrum measurement biosensor based on linear polarization incidence and a test method, which comprises a terahertz wave refractive lens and a subwavelength metal sensing structure. The terahertz wave refractive lens is in a semisphere shape. The subwavelength metal sensing structure is a metal plate, and a plurality of gratings are uniformly distributed on the metal plate. The circular section of the terahertz wave refractive lens is oppositely arranged with the gratings of the subwavelength metal sensing structure, and a to-be-measured gap is formed between the terahertz wave refractive lens and the subwavelength metal sensing structure. The sensor has a simple structure, and the test method is convenient to operate. The chiral terahertz electric field can be locally enhanced in the sensing gap, the sample consumption is reduced, the influence of water absorption in the sample is overcome, the enhanced TCD spectrum measurement of trace chiral biological samples (including solution samples) is realized, the limitation that traditional terahertz spectrum technology cannot detect water-containing solution biological samples is broken through, and the application has innovation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biosensing, and particularly relates to a TCD spectrum measurement biosensor based on linearly polarized incident and a test method. BACKGROUND

[0002] Terahertz (1THz = 10 12 Hz) waves refer to electromagnetic waves with a frequency of 0.1 THz-10 THz and a wavelength of 0.03 mm-3 mm, and the frequency spectrum is located between infrared and microwave. Compared with traditional spectral analysis techniques such as infrared spectrum and X-ray, the skeleton vibration, rotational spectrum and weak intermolecular interaction energy level of many biological organic molecules such as proteins, DNA, RNA, amino acids and sugars are in the terahertz wave band, which makes the terahertz spectrum technology have important application prospects in the study of molecular characteristics of biological macromolecules.

[0003] Chirality is a basic property of nature, which refers to the feature that an object and its mirror image cannot coincide. The structure of a chiral molecule itself does not have mirror symmetry, and the mirror projection of the molecule is an enantiomer with opposite chirality. Most physical properties of chiral molecules that are enantiomers are the same, but there are obvious differences in activity in biological bodies. Therefore, qualitative and quantitative detection of chiral molecules has important significance in the fields of analytical science, chemical biology and drugs.

[0004] At present, the commonly used chiral detection methods mainly include two kinds, chromatography and spectroscopy. Chromatography mainly uses the selective adsorption capacity of the chromatographic column to separate, purify and analyze chiral molecules. However, different chromatographic columns and mobile phases need to be selected for different chiral molecules, which leads to low universality, high difficulty in operation and high analysis cost. Chiral spectroscopy such as circular dichroism (CD) analyzes the characteristics of the sample based on the absorption difference of different chiral light fields of the chiral sample, and is a fast and efficient method indispensable for studying molecular chirality.

[0005] Most biological macromolecules, such as proteins, DNA, RNA, etc., will fold into structures with spatial chirality in space, and are truly chiral molecules. The CD spectrum of proteins mainly comes from two aspects of active chromophores and chiral folding structures. The collective vibration mode of chiral biological macromolecules such as proteins and the change of chiral higher-order folding structure play an important role in the life process, but the characteristic frequency is generally low, which is just in the terahertz frequency band. Therefore, terahertz circular dichroism (TCD) technology can provide more sensitive and efficient detection and analysis for the identification of chiral biological macromolecules and the interaction between molecules.

[0006] However, the circular dichroism response of chiral biomolecules in the terahertz wave band is weak, and it is difficult to directly and effectively detect it. Currently, there is no mature TCD measurement scheme. In addition, the traditional CD measurement needs to use left and right circularly polarized light to incident, but the commonly used terahertz emission source obtains linearly polarized terahertz waves, not circularly polarized waves, which cannot meet the requirement of TCD measurement that different chiral circularly polarized terahertz waves are incident. SUMMARY

[0007] The purpose of the present application is to provide a TCD spectral measurement biosensor based on linearly polarized incident and a test method, which uses twice symmetric angle linearly polarized incident to excite the surface plasmon on the sub-wavelength metal sensing layer, generates a chiral switchable enhanced terahertz chiral electric field, increases the circular dichroism response of the sample, and obtains the broadband TCD spectrum detection of the sample by scanning the incident angle.

[0008] The scheme adopted by the present application to solve the technical problem is a TCD spectral measurement biosensor based on linearly polarized incident, which comprises a terahertz wave refractive lens and a sub-wavelength metal sensing structure. The terahertz wave refractive lens is in the shape of a hemisphere, and the sub-wavelength metal sensing structure is a metal plate with a plurality of gratings uniformly distributed on the metal plate. The circular section of the terahertz wave refractive lens is oppositely arranged with the gratings of the sub-wavelength metal sensing structure, and a to-be-measured gap is formed between the terahertz wave refractive lens and the sub-wavelength metal sensing structure.

[0009] Further, the material of the terahertz wave refractive lens is a high refractive index material in the terahertz wave band, which is one of high-resistance silicon, high-resistance germanium, and methyl pentene polymer.

[0010] Further, the interval size of the gratings of the sub-wavelength metal sensing structure is in the sub-wavelength range, i.e. less than the wavelength of the terahertz wave, and the size is between 5 microns and 900 microns.

[0011] Further, the sub-wavelength metal sensing structure is a one-dimensional periodic structure or a two-dimensional periodic structure.

[0012] Further, the size of the to-be-measured gap can be adjusted, and the size of the gap is in the sub-wavelength range, i.e. less than the wavelength of the incident terahertz wave, and the size is between 5 microns and 900 microns.

[0013] Preferably, the to-be-measured chiral sample in the biosensor can be but is not limited to a solution sample, a gas sample, and a powder sample, and the to-be-measured chiral sample can be filled in the to-be-measured gap or deposited on the surface of the sub-wavelength metal sensing structure.

[0014] Further, the polarization state of the incident terahertz wave in the biosensor is oblique linear polarization.

[0015] Further, the polarization angle of the two incident terahertz waves in the TCD measurement of the biosensor is symmetrical.

[0016] The application also provides a test method of the biosensor for TCD spectrum measurement based on linear polarization incidence, which comprises the following steps: Step 1: filling the sample into the gap to be measured, using the terahertz wave generator to emit the terahertz wave to the terahertz wave refractive lens of the biosensor, adjusting the terahertz polarizer in the incident light path so that the incident terahertz wave is +45° oblique linear polarization, the incident angle is greater than the critical angle of total reflection of the hemispherical columnar lens material, the incident wave is totally reflected on the bottom surface of the hemispherical columnar lens, and the corresponding evanescent wave coupling excites the surface plasmon resonance on the subwavelength metal sensing structure above the bottom surface, generates an enhanced chiral terahertz electromagnetic field, enhances the interaction between the incident wave and the filled chiral sample, amplifies the selective absorption of the chiral sample to the chiral electromagnetic field, and the terahertz signal after the action is emitted from the other side of the hemispherical columnar lens and is detected. Adjusting the polarizer in the outgoing light path, detecting the components of the outgoing signal in the +45° and -45° orthogonal directions respectively, and obtaining the sizes of the left and right circular polarization components of the outgoing signal through data processing; Step 2: similarly, adjusting the terahertz polarizer in the incident light path so that the incident terahertz wave is symmetrical -45° oblique linear polarization, and then generating an enhanced opposite chiral terahertz electromagnetic field, enhancing the interaction between the incident wave and the filled chiral sample, and detecting the terahertz signal after the action from the other side of the hemispherical columnar lens. Adjusting the polarizer in the outgoing light path, detecting the components of the outgoing signal in the +45° and -45° orthogonal directions respectively, and obtaining the sizes of the left and right circular polarization components of the outgoing signal through data processing; Step 3: performing difference calculation on the outgoing signals under the conditions of +45° and -45° linear polarization incidence, and the difference between the two is the TCD signal of the measured chiral sample. By using the electromagnetic enhancement effect of the surface plasmon, the narrowband enhanced TCD signal near the surface plasmon resonance frequency can be obtained; Step 4: by scanning different incident angles and adjusting the coupling gap, the surface plasmon resonance enhancement effect under different frequencies is excited, the circular dichroism response of the sample under different frequencies is enhanced, the narrowband TCD signals corresponding to different incident angles are integrated to obtain a broadband signal, and the broadband enhanced TCD spectrum sensing analysis of the measured chiral sample is realized.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] 1. The biosensor combines the subwavelength metal sensing structure and the hemispherical columnar lens to form a certain small gap as a sample container, thereby reducing the sample consumption and being applicable to the detection of trace samples.

[0019] 2. The sensor efficiently excites surface plasmon resonance on the metal sensing layer structure by incident terahertz waves, amplifies the circular dichroism response of the measured sample by using the electromagnetic enhancement effect, improves the detection sensitivity, and can obtain the enhanced TCD spectrum of the sample.

[0020] 3. Different frequency points of surface plasmon resonance are excited by scanning the incident angle of terahertz waves, the enhanced TCD spectrum near different frequency points is obtained, and the broadband enhanced TCD spectrum of the sample can be obtained through data integration.

[0021] 4. The sensor generates a local enhanced chiral terahertz electric field by using linear polarization instead of circular polarization, and enhances the circular dichroism signal of the chiral sample in the terahertz wave band. The measurement scheme can break through the limitation of traditional circular dichroism spectrum measurement which requires circularly polarized wave incidence, and has innovation.

[0022] 5. The structure of the sensor is simple, the test method is convenient to operate, the local enhanced chiral terahertz electric field can be obtained in the sensing gap, the sample amount is reduced, the influence of water absorption in the sample is overcome, the enhanced TCD spectrum measurement of trace chiral biological samples (including solution samples) is realized, the limitation of traditional terahertz spectrum technology which cannot detect water-containing solution biological samples is broken through, and the innovation is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The figure is a structural schematic diagram of the sensor of the application.

[0024] Figure 2 The figure is a working schematic diagram of the sensor of the application.

[0025] Figure 3 The figure is a dispersion curve diagram of surface plasmon on the sub-wave metal sensing layer in the sensor of the application.

[0026] Figure 4 The figure is a chiral electric field distribution diagram of the metal sensing layer under +45° and -45° twice symmetric linear polarization incidence.

[0027] Figure 5 The figure is a TCD spectrum diagram of a chiral sample (chiral parameter k>0i) obtained by using the sensor of the application.

[0028] Figure 6 The figure is a TCD spectrum diagram of an opposite chiral sample (chiral parameter k<0i) obtained by using the sensor of the application. DETAILED DESCRIPTION

[0029] The application will be further described below with reference to the drawings.

[0030] As Figure 1As shown in the figure, a TCD spectrum measurement biosensor based on linearly polarized incident includes a terahertz wave refractive lens 1, a sub-wavelength metal sensing structure 2, the terahertz wave refractive lens 1 is a hemispherical shape, the sub-wavelength metal sensing structure 2 is a metal plate 21, and a plurality of gratings 22 are uniformly distributed on one side of the metal plate 21, the circular section of the terahertz wave refractive lens 1 is arranged opposite to the grating surface of the sub-wavelength metal sensing structure 2, and the terahertz wave refractive lens 1 and the sub-wavelength metal sensing structure 2 form a to-be-measured gap 3. The material of the terahertz wave refractive lens 1 is a high-refractive-index material in the terahertz wave band, which is one of high-resistance silicon, high-resistance germanium and methyl pentene polymer. The interval size of the grating of the sub-wavelength metal sensing structure is in the sub-wavelength range, that is, less than the wavelength of the terahertz wave, and the size is between 5 microns and 900 microns. The interval size of the to-be-measured gap can be adjusted, and the interval size is in the sub-wavelength range, that is, less than the wavelength of the incident terahertz wave, and the interval size is between 5 microns and 900 microns. The polarization state of the incident terahertz wave in the biosensor is oblique linear polarization. The polarization angles of the two times of incident terahertz waves in the TCD measurement of the biosensor are symmetrical.

[0031] Surface plasmon is a surface wave highly localized on the metal surface, which is very sensitive to the dielectric environment of the metal surface and can be used as a biosensor. The electromagnetic field of the surface plasmon has the characteristics of great electromagnetic enhancement on the sensing metal surface, which can enhance the interaction between the incident wave and the surface matter and amplify the circular dichroism response of the surface matter. The present application is realized by using the designed sensor structure, combining the symmetrical angle oblique linear polarization incidence with the rich physical properties of the evanescent wave of the total reflection prism surface, generating a chiral switchable enhanced terahertz chiral electric field participating in the sample action, and realizing the TCD analysis of the chiral sample. Scanning the incident angle to excite different frequency surface plasmon resonance, using the electromagnetic enhancement effect to obtain the broadband enhanced TCD spectrum of the sample, and realizing the TCD spectrum sensing analysis of the trace chiral sample. Figure 2 As shown in the figure, a TCD spectrum test method based on the above biosensor, specifically: a polarizer P1 is placed in front of the sensor as a polarizer to standardize the linear polarization characteristics of the terahertz incident electric field, and P2 is adjusted to adjust the linear polarization angle of the incident wave (for example, +45° with the horizontal direction), the TM and TE components of the incident wave form parallel overlapping electric and magnetic fields and their phase difference in the sensing layer, and the local enhanced chiral electric field is formed in the sensing gap, and the electromagnetic enhancement effect of the surface plasmon is used to amplify the interaction between the chiral sample and the surface plasmon; adjust P2 so that the polarization of the incident wave is symmetrical angle (for example, -45° with the horizontal direction), realize the chiral switching of the local electric field, and use the opposite chiral field to act on the chiral sample; the difference in the reflection spectrum intensity obtained by two times of symmetrical angle oblique linear polarization incidence is used as the circular dichroism signal of the sample, so as to realize the TCD measurement of the sample.

[0032] As Figure 3 shown in the figure, the dotted line is the wave vector in vacuum, the dash-dot line is the horizontal wave vector of the incident wave in the columnar lens under total reflection incidence, and the curve is the wave vector curve of the plasmonic unit on the surface of the sub-wavelength metal grating structure sensing layer. It can be seen from the figure that the wave vector of the incident wave in the columnar prism and the wave vector curve of the plasmonic unit on the surface of the sensing layer have intersection points, which correspond to the coupling excitation of the surface plasmonic resonance of the incident wave. Under oblique linear polarization incidence, the characteristics of TM and TE polarizations are used to form enhanced chiral electric fields near the surface plasmonic resonance frequency, and the circular dichroism signal of the chiral sample to be measured is enhanced. Changing the incident angle can change the frequency point of the excited surface plasmonic resonance. By scanning the incident angle, the surface plasmonic resonance can be excited in a wide band range, and the wide-band enhanced TCD spectrum detection of the chiral sample can be realized.

[0033] As Figure 4 shown in the figure, under +45° and -45° symmetric linear polarization incidence, the sensing layer of the sensor forms an enhanced chiral terahertz electric field with equal intensity and opposite chirality. Figure 4 (a) is the equal electric field intensity distribution, and (b) and (c) are the corresponding opposite optical chirality distributions. Compared with the circularly polarized wave of the same amplitude, the optical chirality obtained by using the sensor of the application is enhanced by more than 15 times.

[0034] Figure 5 is the reflection spectrum and the corresponding TCD spectrum obtained by using the sensor of the application under two symmetric linear polarization incidences for a chiral sample (k=0.01i). The dash-dot line and the dotted line in the figure correspond to the reflection spectrum under +45° and -45° linear polarization incidence. It can be seen that due to the introduction of the chiral sample, the opposite chiral electric fields generated by the two symmetric incidences have different effects on the sample, resulting in slight differences in the obtained reflection spectrum. The solid line in the figure is the difference curve between the two, which is the TCD spectrum of the chiral sample to be measured.

[0035] Figure 6 is the reflection spectrum and the corresponding TCD spectrum obtained by using the sensor of the application under two symmetric linear polarization incidences for a chiral sample (k=0.01i). The dash-dot line and the dotted line in the figure correspond to the reflection spectrum under +45° and -45° linear polarization incidence. It can be seen that due to the introduction of the chiral sample, the opposite chiral electric fields generated by the two symmetric incidences have different effects on the sample, resulting in slight differences in the obtained reflection spectrum. The solid line in the figure is the difference curve between the two, which is the TCD spectrum of the chiral sample to be measured. Figure 4 is exactly symmetrical, which verifies the TCD spectrum measurement capability of the sensor of the application. By scanning different incident angles to change the excitation frequency of the surface plasmon, the wide-band enhanced TCD spectrum information of the sample to be measured can be obtained.

[0036] The above is the preferred embodiment of the application, and any changes made according to the technical solutions of the application, as long as the generated function does not exceed the scope of the technical solutions of the application, belong to the protection scope of the application.

Claims

1. A method of testing a TCD spectroscopic biosensor based on linearly polarized incident light, characterized by: The sensor comprises a terahertz wave refractive lens and a sub-wavelength metal sensing structure, the terahertz wave refractive lens is in the shape of a hemisphere, the sub-wavelength metal sensing structure is a metal plate, a plurality of gratings are uniformly distributed on the metal plate, a circular section of the terahertz wave refractive lens is arranged opposite to the gratings of the sub-wavelength metal sensing structure, and a to-be-measured gap is formed between the terahertz wave refractive lens and the sub-wavelength metal sensing structure; the test method comprises the following steps: step one: a to-be-measured article is filled in the to-be-measured gap, a terahertz wave generator is used to shoot terahertz waves into the terahertz wave refractive lens of the biosensor, a terahertz polarizer in an incident light path is adjusted, so that the incident terahertz waves are +45° inclined linearly polarized, the incident angle is greater than the critical angle of total reflection of the hemispherical column lens material, total reflection of the incident waves is generated on the bottom surface of the hemispherical column lens, corresponding evanescent wave coupling excitation of surface plasmon resonance on the sub-wavelength metal sensing structure is formed above the bottom surface, an enhanced chiral terahertz electromagnetic field is generated, the interaction between the incident waves and the filled chiral sample is enhanced, the selective absorption of the chiral sample to the chiral electromagnetic field is amplified, and the terahertz signal after the action is shot out from the other side of the hemispherical column lens and is detected; a polarizer in an outgoing light path is adjusted, components of the outgoing signal in +45° and -45° orthogonal directions are detected respectively, and the sizes of left and right circular polarization components of the outgoing signal are obtained through data processing; step two: similarly, the terahertz polarizer in the incident light path is adjusted, so that the incident terahertz waves are symmetrical -45° inclined linearly polarized, and then an enhanced opposite chiral terahertz electromagnetic field is generated, the interaction between the incident waves and the filled chiral sample is enhanced, the terahertz signal after the action is shot out from the other side of the hemispherical column lens and is detected, the polarizer in the outgoing light path is adjusted, the components of the outgoing signal in +45° and -45° orthogonal directions are detected respectively, and the sizes of left and right circular polarization components of the outgoing signal are obtained through data processing; step three: the outgoing signals under the two incident conditions of +45° and -45° linear polarization are subtracted, and the difference between the two is the TCD signal of the measured chiral sample; the electromagnetic enhancement effect of surface plasmon is used, and a narrow-band enhanced TCD signal near the surface plasmon resonance frequency can be obtained; step four: different frequencies of surface plasmon resonance enhancement effects are excited by scanning different incident angles and adjusting the coupling gap, the circular dichroism response of the sample at different frequencies is enhanced, the narrow-band TCD signals corresponding to different incident angles are integrated to obtain a wide-band signal, and wide-band enhanced TCD spectrum sensing analysis of the measured chiral sample is realized.

2. The method according to claim 1, wherein the method is a method for testing a TCD biosensor based on linearly polarized incident light. The material of the terahertz wave refractive lens is a high-refractive-index material in a terahertz wave band, and is one of high-resistance silicon, high-resistance germanium and methyl pentene polymer.

3. The method of claim 1, wherein the method is based on linearly polarized incident light. The interval size of the gratings of the sub-wavelength metal sensing structure is in a sub-wavelength range, that is, less than the wavelength of terahertz waves, and is between 5 microns and 900 microns.

4. The method of claim 1, wherein the method is based on linearly polarized incident light. The sub-wavelength metal sensing structure is a one-dimensional periodic structure or a two-dimensional periodic structure.

5. The method of claim 1, wherein the method is based on linearly polarized incident light. The interval size of the to-be-tested gap can be adjusted, the interval size is in a sub-wavelength range, that is, less than the wavelength of the incident terahertz wave, and the interval size is between 5 microns and 900 microns.

6. The method of claim 1, wherein the method is based on linearly polarized incident light. The to-be-tested chiral sample in the biosensor can be a solution sample, a gas sample or a powder sample, and the to-be-tested chiral sample can be filled in the to-be-tested gap or deposited on the surface of the sub-wavelength metal sensing structure.

7. The method of claim 1, wherein the method is based on linearly polarized incident light. The polarization state of the incident terahertz wave in the biosensor is oblique linear polarization.

8. The method of claim 1, wherein the method is based on linearly polarized incident light. The polarization angles of the two incident terahertz waves during TCD measurement in the biosensor are symmetrical.

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