Terahertz metasurface immunosensor modified by single-stranded DNA (Deoxyribose Nucleic Acid) aptamer

Abstract

The invention discloses a terahertz metasurface biosensor which is modified by a single-stranded DNA (deoxyribonucleic acid) nucleic acid aptamer and is used for specifically detecting a tumor necrosis factor-alpha. Under the simulation condition, the surface of the biosensor is covered with a layer of analyte with the thickness of 20 microns, and when the refractive index of the analyte is changed from n = 1 to n = 2, the theoretical sensitivity of the metasurface biosensor can reach 124.71 GHz / RIU. In an experiment, the metasurface is prepared on a copper-plated polyethylene glycol terephthalate sheet by using photoetching and chemical corrosion processes. Then, according to the characteristic that the nucleic acid aptamer is specifically combined with the tumor necrosis factor-alpha, the nucleic acid aptamer is modified on the surface of the sensor, so that the super-surface biological immunosensor is prepared, the concentration detection of the tumor necrosis factor-alpha is realized, the detection limit reaches 0.1 ng / ml, and the detection sensitivity can reach 13.9 GHz / 1g (ng / ml). Besides, ovalbumin and whey protein with the same concentration are compared and detected, and the result shows that only the tumor necrosis factor-alpha can be obviously distinguished, so that the sensor has a specific detection function. The terahertz metasurface immunosensor provided by the invention realizes the specific detection of the tumor necrosis factor-alpha. The work can be used for biomarker detection and early diagnosis of diseases.

Description

Technical Field

[0001] The present invention relates to the fields of optics and biomedicine, and particularly to a terahertz metasurface immunosensor modified with single-stranded DNA aptamers. Technical Background

[0002] Tumor necrosis factor alpha (TNF-α) is a cytokine with a wide range of biological functions. Abnormal regulation of TNF-α production is associated with a variety of human diseases, including Alzheimer's disease, cancer, severe depression, psoriasis, and inflammatory bowel disease. In addition to its cytotoxicity to tumor cells themselves, TNF-α can also destroy the vascular tissue around solid tumors and block the blood nutrient supply to tumors through the formation of thrombi, ultimately leading to tumor necrosis. TNF-α at concentrations above a certain level can significantly reduce the pressure in the interstitial tissue around solid tumors, expand the interstitial space of the surrounding epithelial tissue, and change the permeability of the surrounding blood vessels, enabling chemotherapeutic drugs to reach the vicinity of the target tissue. Therefore, as one of the important biological indicators in immunological research, it is of great clinical significance to establish a rapid, sensitive, and accurate method for detecting TNF-α.

[0003] Currently, various methods have been used for TNF-α detection, including enzyme-linked immunosorbent assay, radioimmunoassay, and bioassay. In addition, other quantitative methods for TNF-α determination include chemiluminescence, dissociation-enhanced lanthanide fluorescence immunoassay, time-resolved immunofluorescence assay, enzyme-amplified lanthanide luminescence, matrix-assisted laser desorption / ionization mass spectrometry, and immunological polymerase chain reaction. However, most of these methods have some drawbacks in detecting TNF-α content, such as being harmful to health and time-consuming, requiring professional personnel and complex instruments. Therefore, as an alternative to these methods, it is necessary to develop new biosensors or analytical methods with rapid response, high sensitivity, and convenient operation.

[0004] Aptamers are DNA or RNA molecules isolated by systematic evolution of ligands by exponential enrichment (SELEX), which can bind to other targets such as proteins, metal ions, small molecules, polypeptides, and even whole cells with high affinity and specificity. At the same time, aptamers have a smaller molecular weight, better stability, are easier to modify, are non-immunogenic, and have a short production cycle compared to antibodies. They can be synthesized artificially, eliminating a series of processes such as animal immunization, feeding, protein extraction, and purification. In addition, the essence of most aptamer-antigen interactions is the interaction between nucleotides and proteins, generally one of electrostatic attraction, hydrogen bonding, or van der Waals forces. At the same time, these weak intermolecular interactions can be observed by terahertz spectroscopy.

[0005] Terahertz waves are located between microwaves and infrared rays in the electromagnetic wave spectrum. The photon energy of its radiation is much lower than that of X-rays, so it will not cause damage to biological tissue structures and avoid the side effect of ionizing biological molecules. Moreover, terahertz waves can effectively stimulate the interactions between biological molecules, including hydrogen bonds, van der Waals forces, vibrations between molecular structures, etc. Therefore, terahertz spectroscopy is widely used in the sensing and detection of proteins, viruses, antibiotics, DNA or RNA, and cells, etc.

[0006] Metasurfaces are two-dimensional artificial structured materials composed of sub-wavelength units, and their properties are determined by the physical structures of the artificially designed units. Therefore, by reasonably selecting materials and designing the unit structures of metasurfaces, unique electromagnetic phenomena can be generated, such as: negative refractive index, electromagnetically induced transparency, artificial chirality, etc. Compared with electrical and chemical sensors, metasurfaces have the advantages of anti-electromagnetic interference and good stability, and are a powerful optical sensing platform.

[0007] However, no matter how the structure of the metasurface is designed, it can only have non-specific interactions with analytes and cannot recognize specific substances. Therefore, the method of combining nucleic acid aptamers with terahertz metasurface biosensors based on the specific recognition and binding reaction between nucleic acid aptamers and antigens can perfectly solve this problem. Summary of the Invention

[0008] The object of the present invention is to provide a terahertz metasurface immunosensor modified with single-stranded DNA nucleic acid aptamers, which can solve one or more of the above technical problems.

[0009] In order to achieve the above object, the technical solution proposed by the present invention is as follows:

[0010] A terahertz metasurface immunosensor modified with single-stranded DNA nucleic acid aptamers, characterized in that the terahertz metasurface immunosensor is composed of an asymmetric metal double split-ring metasurface and a functional layer of composite single-stranded DNA nucleic acid aptamers;

[0011] The asymmetric metal double split-ring metasurface is composed of a metal copper layer and a substrate layer from top to bottom;

[0012] The metal copper layer is composed of asymmetric double split-rings;

[0013] Define the center of the asymmetric metal double split-ring metasurface as the origin, the X-axis is perpendicular to the central axis of the asymmetric double split-ring, the Y-axis is parallel to the central axis of the asymmetric double split-ring, and the Z-axis is perpendicular to the asymmetric metal double split-ring metasurface.

[0014] The functional layer of the composite single-stranded DNA aptamer is the area formed by sequentially adding gold nanospherical particles, reduced graphene oxide, single-stranded DNA aptamer, and bovine serum albumin onto the asymmetric metal split-ring metasurface;

[0015] The asymmetric metal double split-ring metasurface is coupled with terahertz waves that are vertically incident and have an electric field direction along the X-axis, generating a transmission spectrum with a Fano resonance shape. The functional layer of the composite single-stranded DNA aptamer utilizes its characteristic of specifically binding to target molecules to achieve the specific detection of target molecules by the terahertz asymmetric metal split-ring metasurface.

[0016] The unit structure of the asymmetric metal double split-ring metasurface is composed of two materials, copper and polyethylene terephthalate, and the functional layer of the composite single-stranded DNA aptamer is composed of gold nanospherical particles, reduced graphene oxide, single-stranded DNA aptamer, and bovine serum albumin;

[0017] The copper layer is composed of an asymmetric double split-ring structure;

[0018] The inner ring radius of the asymmetric double split-ring structure is 40 μm, the outer ring radius is 70 μm, and the height is 200 nm. Among them, along the opening direction, the central angle of the semi-ring on one side is 180°, and the central angle of the annular structure on the other side is 120°;

[0019] The side length of the substrate layer is 190 μm, and the height is 30 μm;

[0020] The size of the gold nanospherical particles in the functional layer of the composite single-stranded DNA aptamer is 80 nm;

[0021] The concentration of the reduced graphene oxide solution in the functional layer of the composite single-stranded DNA aptamer is 1 mg / ml;

[0022] The concentration of the single-stranded DNA aptamer solution in the functional layer of the composite single-stranded DNA aptamer is 5 μmol / ml.

[0023] The mass fraction of the bovine serum albumin solution in the functional layer of the composite single-stranded DNA aptamer is 1%.

[0024] The technical effects of the present invention are as follows:

[0025] (1) The lithography and etching processes used in the present invention are compatible with the CMOS process, which helps the integrated development of terahertz sensors and detectors.

[0026] (2) The polyethylene terephthalate material used in the present invention has advantages such as good physical properties, strong chemical stability, and low price, and it has a wide range of applications.

[0027] (3) The terahertz metasurface immunosensor proposed in the present invention has the advantages of a wide detection range and no need for labeling. Therefore, this sensor has the potential for biomarker detection and early disease diagnosis.

[0028] (4) In the present invention, based on the functional layer of composite single-stranded DNA aptamer, by utilizing its characteristic of specifically binding to target molecules, specific detection of target molecules by the terahertz asymmetric metal split-ring metasurface is realized. This provides an idea for the development of bio-immunosenors. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0030] In the drawings:

[0031] Figure 1 is a schematic diagram of the terahertz metasurface sensor.

[0032] Figure 2 is a schematic diagram of the unit cell of the terahertz metasurface sensor.

[0033] Figure 3 is the surface current density of the metasurface unit structure and the corresponding equivalent circuit diagram at 0.5824 THz.

[0034] Among them, in Figure 3 the abscissa of the left figure is the frequency (THz) of the incident terahertz wave, and the ordinate is the transmittance.

[0035] Figure 4 is the simulated transmission spectrum of the metasurface.

[0036] Among them, in Figure 4 the abscissa is the frequency (THz) of the incident terahertz wave, and the ordinate is the transmittance.

[0037] Figure 5 is the influence of structural parameters on the transmission spectrum of the metasurface.

[0038] Among them, in Figure 5 the abscissa is the frequency (THz) of the incident terahertz wave, the ordinate is the structural parameter (μm), and the color depth represents the transmittance.

[0039] Figure 6 is the relationship between the transmission spectrum of the metasurface and the tilt angle. The right figure is a partial enlarged view of the transmission spectrum.

[0040] Among them, in Figure 6In it, the abscissa is the frequency (THz) of the incident terahertz wave, the ordinate is the transmittance, and different line shapes represent different incident angles of the terahertz wave.

[0041] Figure 7 It is the refractive index and thickness simulation of the surface-covered analyte by the metasurface sensor and the corresponding frequency shift amount diagrams respectively.

[0042] Among them, in Figure 7 In it, the abscissa of the first column is the frequency (THz) of the incident terahertz wave, and the ordinate is the transmittance. The abscissa of the second column in the first row is the refractive index of the analyte, and the abscissa of the second column in the second row is the thickness (μm) of the analyte. The ordinate of the second column is the frequency shift amount (GHz) of the resonance peak.

[0043] Figure 8 It is the scanning electron microscope image of the metasurface sensor.

[0044] Figure 9 It is the scanning electron microscope image of the gold nanospherical particles.

[0045] Figure 10 It is the scanning electron microscope image of the functionalized gold nanoparticles binding with tumor necrosis factor-α.

[0046] Figure 11 It is the experimental transmission spectrum of the metasurface.

[0047] Among them, in Figure 11 In it, the abscissa is the frequency (THz) of the incident terahertz wave, and the ordinate is the transmittance.

[0048] Figure 12 It is the schematic diagram of the surface modification of the metasurface sensor.

[0049] Among them, in Figure 12 In it, AuNPs / 4℃ / 3hours means that after adding gold nanoparticles to the sensor surface, the sensor is left standing at 4℃ for 3 hours. RGO / 25℃ / 20mins means that after adding reduced graphene oxide to the sensor surface, the sensor is left standing at 25℃ for 20 minutes. Aptamer / 25℃ / 1hour means that after adding nucleic acid aptamer to the sensor surface, the sensor is left standing at 25℃ for 1 hour. BSA / 25℃ / 20mins means that after adding bovine serum albumin to the sensor surface, the sensor is left standing at 25℃ for 20 minutes. Antigen / 25℃ / 1hour means that after adding antigen to the sensor surface, the sensor is left standing at 25℃ for 1 hour.

[0050] Figure 13 It is the transmission spectrum diagram of different concentrations of TNF-α.

[0051] Among them, in Figure 13In it, the abscissa is the frequency (THz) of the incident terahertz wave, the ordinate is the transmittance, and the inset is the partial enlarged view of the resonance peak corresponding to different concentrations of TNF-α.

[0052] Figure 14 It is the linear fitting of the frequency shift amount and the concentration of tumor necrosis factor-α, and the linear fitting of the minimum value of the transmission spectrum and the concentration of tumor necrosis factor-α.

[0053] Among them, in Figure 14 the abscissa is the logarithm (lgC TNF-α (ng / ml)) of different concentrations of tumor necrosis factor-α, the left ordinate is the frequency shift amount (GHz) of the resonance peak, and the right ordinate is the minimum value (GHz) of the transmission spectrum.

[0054] Figure 15 It is the transmission spectrum of different proteins.

[0055] Among them, in Figure 15 the abscissa is the frequency (THz) of the incident terahertz wave, the ordinate is the transmittance, OVA represents ovalbumin, and WP represents whey protein.

[0056] Figure 16 It is the frequency shift amount of different proteins.

[0057] Among them, in Figure 16 the abscissa is different types of proteins, and the coordinate in the right Z-axis direction is the frequency shift amount (GHz) of the resonance peak. OVA represents ovalbumin, and WP represents whey protein. Specific embodiments

[0058] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with embodiments and the accompanying drawings. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and do not limit the present invention.

[0059] Figure 1 It is a schematic diagram of the metasurface sensor. The terahertz wave is vertically incident on the sensor surface, and the transmission spectrum is measured by a terahertz frequency-domain spectrometer to study the optical induction behavior of the metasurface immunosensor with different concentrations of target molecules added.

[0060] Define the center of the asymmetric metal double split-ring metasurface as the origin, the X-axis is perpendicular to the central axis of the asymmetric double split-ring, the Y-axis is parallel to the central axis of the asymmetric double split-ring, and the Z-axis is perpendicular to the asymmetric metal double split-ring metasurface.

[0061] Figure 2 It is a schematic diagram of the unit cell of the terahertz metasurface sensor.

[0062] The asymmetric metal double split-ring metasurface unit structure is composed of two materials, namely copper and polyethylene terephthalate.

[0063] The copper layer is composed of an asymmetric double split-ring structure. The inner ring radius of the asymmetric double split-ring structure is 40 μm, the outer ring radius is 70 μm, and the height is 200 nm. Among them, along the opening direction, the central angle of the semi-ring on one side is 180°, and the central angle of the other annular structure is 120°. The side length of the substrate layer is 190 μm and the height is 30 μm.

[0064] Figure 3 The surface current density of the metasurface unit structure and the corresponding equivalent circuit diagram at 0.5824 THz. The surface current of the metal structure forms a loop along the gap, forming a strong magnetic response.

[0065] Figure 4 This is the simulated transmission spectrum of the metasurface. Among them, the minimum value of the transmission spectrum is located at 0.5824 THz.

[0066] Figure 5 This is the influence of structural parameters on the transmission spectrum of the metasurface. When the outer semi-ring R or the inner semi-ring radius r increases, the resonance frequency shows an obvious red shift, indicating that the resonance frequency is very sensitive to the change of the structural line width. In addition, the changes of the period p and the substrate thickness greater than 20 μm have no obvious influence on the resonance frequency.

[0067] Figure 6 This is the relationship between the transmission spectrum of the metasurface and the tilt angle. The right figure is the local enlarged view of the transmission spectrum. Considering that there may be a certain angle when the electromagnetic wave is incident on the metasurface during the experimental test. Therefore, the angle of the incident electromagnetic wave is changed in the simulation to analyze the change of the transmission spectrum. When the tilt angle changes from 0° to 60°, the resonance peak will produce a frequency shift with the increase of the tilt angle.

[0068] Figure 7 This is the simulation of the refractive index and thickness of the analyte covered on the surface of the metasurface sensor and the corresponding frequency shift diagrams respectively. Among them, a 20-μm-thick analyte is covered on the surface of the biosensor. When the refractive index of the analyte changes from n = 1 to n = 2, the sensitivity S = Δf / Δn (Δf represents the change in the resonance frequency, and Δn represents the change in the refractive index) can be calculated by the sensitivity calculation formula of the sensor, and the sensitivity S = 124.71 GHz / RIU.

[0069] Figure 8 This is the scanning electron microscope image of the metasurface sensor. The structure is clear and complete, and the etching process is well controlled, so that the errors and defects in manufacturing are within the controllable range.

[0070] Figure 9It is a scanning electron microscope image of gold nanospherical particles, showing good uniformity in shape and size.

[0071] Figure 10 It is a scanning electron microscope image of functionalized gold nanoparticles binding to tumor necrosis factor-α.

[0072] Figure 11 It is the experimental transmission spectrum of the metasurface. Among them, the minimum value of the transmission spectrum is located at 0.5986 THz, which is close to the simulation effect.

[0073] The functional layer of the composite single-stranded DNA aptamer is composed of gold nanospherical particles, reduced graphene oxide, single-stranded DNA aptamer, and bovine serum albumin.

[0074] Figure 12 It is a schematic diagram of the surface modification of the metasurface sensor.

[0075] Among them, in Figure 12 First step: First, wash and dry the sensor. Then add gold nanoparticles with a diameter of 80 nm to the surface of the sensor and incubate at 4 °C for 3 hours. In this step, the gold nanoparticles are used to amplify the signal and provide a suitable microenvironment for aptamer immobilization. Second step: Drop the reduced graphene oxide (RGO) solution onto the surface and incubate at 25 °C for 20 minutes. In this step, the reduced graphene oxide is used for signal amplification and the immobilization of gold nanoparticles, thus providing a binding site for the nucleic acid aptamer. Third step: Add the nucleic acid aptamer solution to the surface of the sensor and incubate at 25 °C for 1 hour. After that, wash several times with phosphate buffer solution (0.01 mol / L, pH = 7.4) to remove the excess aptamer. In this step, the nucleic acid aptamer can specifically recognize and bind to the target molecule, which is used to improve the detection sensitivity of TNF-α. Fourth step: Add a 1% bovine serum albumin solution to the surface of the sensor, and then let the sensor stand at 25 °C for 30 minutes. After that, wash with phosphate buffer solution (0.01 mol / L, pH = 7.4). The purpose of this step is to use bovine serum albumin to occupy the sites that may exist where the aptamer and gold nanoparticles are not bound, to avoid the direct attachment of the analyte to this site and thus produce non-specific adsorption.

[0076] Figure 13 It is the transmission spectrum obtained by experimental measurement after dropping different concentrations of tumor necrosis factor-α onto the surface of the metasurface immunosensor. Compared with the case without analyte, the resonance peak redshifts and this redshift is concentration-dependent.

[0077] Figure 14It is the linear fitting of the frequency shift amount and the concentration of tumor necrosis factor-α, and the linear fitting of the minimum value of the transmission spectrum and the concentration of tumor necrosis factor-α. When the concentration of tumor necrosis factor-α increases from 0.1 ng / ml to 100 ng / ml, the resonance frequency shifts from 0.5986 THz to 0.5334 THz, and the total frequency shift amount is as high as 65.1 GHz. The fitting relationship between the concentration of tumor necrosis factor-α and the frequency shift is Δf = 13.9 lgC TNF-α (ng / ml) + 26.1. The fitting result shows that in the range of 0.1 ng / ml to 100 ng / ml, the frequency shift has a linear relationship with different concentrations of tumor necrosis factor-α. According to the linear fitting function S = (Δf - A) / C, the sensitivity of the sensor for detecting antigens can be obtained, where S is the sensitivity, Δf is the frequency shift amount, A is the calculation constant, and C is the analyte concentration. Therefore, the detection sensitivity of the nucleic acid aptamer-modified sensor for TNF-α is S = 13.9 GHz / lg(ng / ml).

[0078] Figure 15 It is the transmission spectra of different proteins. Three proteins were experimentally measured: tumor necrosis factor-α (TNF-α), ovalbumin (OVA), and whey protein (WP). Among them, ovalbumin and whey protein do not specifically bind to the TNF-α nucleic acid aptamer, so their comparison with TNF-α can be used to verify the specific recognition of the sensor. In each experiment, the sensor was modified with the same volume and the same concentration of TNF-α nucleic acid aptamer. Once the surface modification was completed, the same volume and the same concentration of various proteins were immediately dropped onto the sensor, and then left standing at 25 °C for 1 hour. Then, it was washed repeatedly 3 or 4 times with phosphate buffer (PBS, pH = 7.4). Therefore, the experimental results will not be affected by other unbound proteins.

[0079] Figure 16 The frequency shift of TNF-α is much larger than that of the other two proteins. This is attributed to the fact that when TNF-α molecules are dropped onto the surface of the immunosensor, the TNF-α nucleic acid aptamer can quickly recognize TNF-α molecules and react with them, forming an aptamer-TNF-α immune complex precipitate and adsorbing on the surface of the sensor. At the same time, the formation of the immune complex may play a role as a mass transfer and electron transfer blocking layer. Therefore, it blocks the electron transfer channel and hinders the transfer of electrons to the electrode surface, resulting in a change in the dielectric constant. However, the other two proteins do not react with the TNF-α nucleic acid aptamer, and only a small amount adheres to the surface of the sensor.

[0080] In the present invention, a terahertz metasurface immunosensor modified with single-stranded DNA aptamer is designed, and the concentration detection of tumor necrosis factor-α is realized. The detection limit reaches 0.1 ng / ml, and the detection sensitivity can reach 13.9 GHz / lg(ng / ml). In addition, by comparing the detection of ovalbumin and whey protein at the same concentration, the results show that only tumor necrosis factor-α can be significantly distinguished, thus verifying the function of specific detection of this sensor.

[0081] We completed the preparation of the metasurface on a copper-plated polyethylene terephthalate sheet using photolithography and chemical etching processes. Subsequently, according to the specific binding characteristics of the aptamer and tumor necrosis factor-α, the aptamer was modified on the sensor surface, thus preparing the metasurface bio-immunosensor. This work can be used for biomarker detection and early disease diagnosis.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A terahertz metasurface immunosensor modified with a single-stranded DNA aptamer, characterized in that, The above-mentioned metasurface immunosensor is composed of an asymmetric metal double split-ring metasurface and a functional layer of composite single-stranded DNA aptamer; The above-mentioned asymmetric metal double split-ring metasurface is composed of a copper layer and a substrate layer from top to bottom; The copper layer is composed of asymmetric double split-rings; Define the center of the above-mentioned asymmetric metal double split-ring metasurface as the origin, the X-axis is perpendicular to the central axis of the asymmetric double split-ring, the Y-axis is parallel to the central axis of the asymmetric double split-ring, and the Z-axis is perpendicular to the asymmetric metal double split-ring metasurface. The functional layer of the composite single-stranded DNA aptamer is the area formed after gold nanospherical particles, reduced graphene oxide, single-stranded DNA aptamer and bovine serum albumin are successively added onto the asymmetric metal split-ring metasurface; The above-mentioned asymmetric metal double split-ring metasurface is coupled with a terahertz wave that is vertically incident and the electric field direction is along the X-axis, generating a transmission spectrum with a Fano resonance shape. The functional layer of the composite single-stranded DNA aptamer realizes the specific detection of target molecules by the terahertz asymmetric metal split-ring metasurface by virtue of its characteristic of specifically binding to target molecules.

2. The terahertz metasurface immunosensor modified by a single-stranded DNA aptamer according to claim 1, wherein The unit structure of the above-mentioned asymmetric metal double split-ring metasurface is composed of two materials, copper and polyethylene terephthalate, and the functional layer of the composite single-stranded DNA aptamer is composed of gold nanospherical particles, reduced graphene oxide, single-stranded DNA aptamer and bovine serum albumin; The above-mentioned copper layer is composed of an asymmetric double split-ring structure; The inner ring radius of the above-mentioned asymmetric double split-ring structure is 40 microns, the outer ring radius is 70 microns, and the height is 200 nanometers. Among them, along the opening direction, the central angle of the semi-ring on one side is 180°, and the central angle of the annular structure on the other side is 120°; The side length of the above-mentioned substrate layer is 190 microns and the height is 30 microns; The size of the gold nanospherical particles in the functional layer of the composite single-stranded DNA aptamer is 80 nanometers; The concentration of the reduced graphene oxide solution in the functional layer of the composite single-stranded DNA aptamer is 1 mg / ml; The concentration of the single-stranded DNA aptamer solution in the functional layer of the composite single-stranded DNA aptamer is 5 μmol / ml. The mass fraction of the bovine serum albumin solution in the functional layer of the composite single-stranded DNA aptamer is 1%.

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