CN110763659A - A kind of optical fiber SPR biosensor and preparation method thereof - Google Patents

Abstract

The invention provides an optical fiber SPR biosensor and a preparation method thereof. The sensor adopts a sensing structure based on a U-shaped optical fiber with a molybdenum disulfide-gold film interlayer. The middle curved part of the U-shaped optical fiber is a sensing area. The surface of the optical fiber is coated with molybdenum disulfide coating, the surface of the molybdenum disulfide coating is coated with a gold film layer, and the surface of the gold film is immobilized by dopamine. The SPR biosensor proposed in the present invention adopts an optical fiber-molybdenum disulfide-gold film sandwich structure. Molybdenum disulfide has a larger band gap and a higher light absorption efficiency, which can stimulate a stronger SPR effect and enhance the surface electric field of the sensor. It can effectively improve the sensitivity of the sensor. The dopamine-immobilized antibody is used on the surface of the sensor to realize the measurement of antigen with high sensitivity and low detection limit, which makes the sensor have a wider application in biological detection.

Description

A kind of optical fiber SPR biosensor and preparation method thereof

technical field

The invention relates to the technical field of biosensors, in particular to an optical fiber SPR biosensor and a preparation method thereof.

Background technique

In recent years, the application of surface plasmon resonance (SPR) technology in various fields has set off a research boom, such as food safety testing, environmental monitoring, medical diagnosis, bioengineering, etc. In particular, the application of SPR in biosensing technology has attracted extensive attention and research, and various high-performance biosensors have appeared one after another. Among them, fiber-optic biosensors are popular because of their small size, label-free, and high detection speed. of favor. Surface plasmon resonance (SPR) biosensor is one of the most rapidly developed and comprehensive optical sensors, but the SPR biosensor uses metal with negative dielectric constant as the excitation element, which will cause the internal loss of the sensor. increases, thereby affecting the sensitivity and detection limit of the sensor.

After entering the 21st century, materials science has entered a new stage of rapid development. Many new materials have been discovered and aroused great interest. Some advanced and practical two-dimensional materials such as graphene, transition metal compounds (TMDCs), Black phosphorus, etc., are used to improve the performance of biosensors, so as to make up for the limitations of low sensitivity and high detection limit in SPR biosensors. Accordingly, the present invention provides a U-shaped fiber-based molybdenum disulfide- Gold film sandwich optical fiber SPR biosensor and preparation method thereof.

SUMMARY OF THE INVENTION

In order to solve the problems of low sensitivity and high detection limit of the existing optical fiber SPR biosensor, the present invention proposes an optical fiber SPR biosensor and a preparation method thereof. The sensor is based on a U-shaped optical fiber molybdenum disulfide-gold film sandwich sensing structure , its sensitivity has been significantly improved, and the detection limit has been significantly reduced.

One aspect of the present invention provides an optical fiber SPR biosensor. The sensor adopts a sensing structure based on a U-shaped optical fiber with a molybdenum disulfide-gold film sandwich. A molybdenum disulfide coating is applied, the surface of the molybdenum disulfide coating is plated with a gold film, and the surface of the gold film is immobilized by dopamine.

Further, the molybdenum disulfide coating is coated on the surface of the optical fiber by an electrostatic self-assembly method.

Further, the length of the sensor fiber is 30-40 cm, and the length of the sensing area is 20-30 mm.

Further, the thickness of the molybdenum disulfide coating is 0.65-13 nm.

Further, the thickness of the gold film layer is 40-55 nm.

Preferably, the total thickness of the molybdenum disulfide-gold film interlayer is 60 nm.

Further preferably, the thickness of the molybdenum disulfide coating is 10 nm, and the thickness of the gold film layer is 50 nm.

Another aspect of the present invention provides a method for preparing the above-mentioned optical fiber SPR biosensor, the method comprising the following steps:

(a) Optical fiber pretreatment: take 30cm～40cm multimode optical fiber, remove the coating layer with a length of 20～30mm in the middle of the optical fiber, remove the impurities attached to the surface of the optical fiber in the sensing area, form the sensing area, bend the optical fiber to form a U shape, Use the outer flame of the alcohol lamp to heat the curved part to fix the shape;

(b) Preparation of molybdenum disulfide coating: soak the bent part of the U-shaped optical fiber in piranha solution for 0.5-1.5 hours, take it out and soak it in 10mg/ml-1g/ml PDDA aqueous solution for 0.5-1.5 hours, and then soak it in 0.1 Molybdenum disulfide nanosheets are soaked in water or ethanol dispersion of mg/ml～200mg/ml for 3～12 hours; PDDA solution is used as the connection medium between optical fiber and molybdenum disulfide, PDDA is positively charged, and molybdenum disulfide nanosheets Negatively charged, molybdenum disulfide is fixed on the surface of the fiber by electrostatic adsorption;

(c) deposition of gold film layer: the gold film is deposited by a magnetron sputtering apparatus, the discharge time is 1.5 to 5 min, the current is 0 to 10 mA, and the thickness of the gold film is controlled by adjusting the discharge time and current;

(d) Antibody immobilization: Immerse the bent part of the U-shaped optical fiber in a dopamine solution of 1 mg/ml to 100 mg/ml for half an hour. Dopamine polymerizes in water to form polydopamine on the surface of the gold film in the sensing area. Dry in an incubator for half an hour, and then immerse the sensor sensing area in 0.01mg/ml ~ 1mg/ml antibody solution for 12 hours; polydopamine is used as the connecting medium between the gold film and the immobilized antibody, and the antibody is immobilized on the surface of the gold film.

The principle of the present invention is:

Transition metal dichalcogenides (TMDC), similar to graphene, belong to two-dimensional nanomaterials, molybdenum disulfide and tungsten disulfide belong to TMDC, compared with graphene, molybdenum disulfide has a larger band gap and higher light absorption efficiency, and they also have high specific surface area and good biocompatibility, which makes it possible to introduce transition metal dichalcogenides into SPR sensors, which can better improve the sensitivity of the sensors.

The molybdenum disulfide-gold film sandwich optical fiber SPR biosensor based on the U-shaped optical fiber proposed by the present invention, the gold film SPR sensor has high sensitivity, and the molybdenum disulfide has a large band gap and a higher light absorption efficiency, which can further Enhance the surface electric field to improve the sensitivity; the specific binding between the antibody and the antigen causes the resonance wavelength shift, according to the ratio of the biological analyte concentration and the resonance wavelength shift to realize the high sensitivity measurement of the antigen, which is realized by the calculation of the limit test performance index LOD The measurement of the lowest detection limit makes the sensor have a better application in the field of biological detection.

The sensor coated with molybdenum disulfide nanosheets between the gold film and the optical fiber has better sensitivity performance than the sensor coated with molybdenum disulfide nanosheets on the surface of the gold film, due to the bending of the fiber, the light conducted in the core leaks to the In the cladding, the light conducted in the cladding does not satisfy the condition of total reflection, so most of the light in the cladding mode disappears in the surrounding medium. In a U-shaped fiber SPR sensing system, part of the light energy generated by the disappearance of the cladding mode is used to excite the SPR phenomenon, while the remaining loss is in the surrounding medium. When only the gold film exists on the surface of the fiber, the light energy absorbed by the gold film is not enough to support the strong excitation of the SPR phenomenon. When molybdenum disulfide nanosheets were added between the fibers and the gold film, due to the high light absorption rate of molybdenum disulfide (~ ₅ %), the presence of MoS2 could effectively increase the absorption of light energy, thereby promoting stronger stimulated by the SPR phenomenon. Meanwhile, since the monolayer _MoS2 is a direct bandgap semiconductor, the absorbed energy is used for electron transfer, and the energy loss during the transfer process is small. More electrons are transferred from the molybdenum disulfide to the gold film, thereby increasing the surface electric field strength of the sensor. Coating a layer of molybdenum disulfide on the surface of the gold film of the sensor will only increase the utilization of light energy absorbed by the sensor system. However, on the basis of the presence of a molybdenum disulfide coating between the gold film and the optical fiber, the utilization rate of the absorbed light energy is improved, and the absorption rate of the light energy is improved.

The beneficial effects of the present invention compared with the prior art are:

1. The molybdenum disulfide-gold film sandwich optical fiber SPR biosensor based on the U-shaped optical fiber proposed by the present invention has a higher sensitivity through the molybdenum disulfide-gold film sandwich structure;

2. The functionalized sensor that uses dopamine-immobilized antibody to detect human IgG on the sensor surface has excellent biosensing properties, which can better reduce the detection limit; different types of antigens can be immobilized with dopamine to realize the detection of different antibodies;

3. Using a sandwich mechanism, the internal molybdenum disulfide will not fall off while enhancing the sensitivity, which enhances the stability of the sensing structure;

To sum up, the present invention solves the problems of low sensitivity and high detection limit of the existing optical fiber SPR biosensor, and provides a new solution for the detection of low-concentration biological analytes.

Description of drawings

1 is a schematic structural diagram of a U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor in Example 1 of the present invention;

2 is a schematic structural diagram of a U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor system in Example 1 of the present invention;

3 is a schematic structural diagram of a U-shaped optical fiber-based gold-film optical fiber SPR biosensor in Embodiment 1 of the present invention;

4 is a schematic structural diagram of an optical fiber SPR biosensor based on U-shaped optical fiber gold film molybdenum disulfide in Example 1 of the present invention;

FIG. 5 is a transmission spectrum diagram of the U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor in ethanol solutions of different refractive indices in Example 1 of the present invention;

Fig. 6 is the refractive index sensitivity fitting curve of the U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor in Example 1 of the present invention;

Fig. 7 in Example 1 of the present invention, the resonant wavelength of the U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor in different concentrations of igG solution changes with time;

Fig. 8 The change of the resonance wavelength shift amount of the U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor with the concentration of igG solution in Example 1 of the present invention;

9 is a linear fitting curve of the resonant wavelength shift of the U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor in Example 1 of the present invention in the range of igG concentration of 5-20 μg/ml;

Reference number:

1. Multimode fiber core; 2. Fiber cladding; 3. Molybdenum disulfide coating; 4. Gold film; 5. Antibody-goat anti-human immunoglobulin;

A. Molybdenum disulfide-gold film sandwich fiber SPR biosensor with U-shaped fiber; B, broadband light source; C, spectrometer; D, multimode fiber optical path; E, computer; F, beaker;

Detailed ways

It should be noted that the embodiments of the present invention and the features of the embodiments may be combined with each other under the condition of no conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is only a part of the embodiments of the present invention, but not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the invention unless specifically stated otherwise. Meanwhile, it should be understood that, for convenience of description, the dimensions of various parts shown in the accompanying drawings are not drawn in an actual proportional relationship. Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the authorized specification. In all examples shown and discussed herein, any specific values should be construed as illustrative only and not limiting. Accordingly, other examples of exemplary embodiments may have different values. It should be noted that like numerals and letters refer to like items in the following figures, so once an item is defined in one figure, it does not require further discussion in subsequent figures.

In the description of the present invention, it should be understood that the orientations indicated by orientation words such as "front, rear, top, bottom, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" etc. Or the positional relationship is usually based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and these orientation words do not indicate or imply the indicated device or element unless otherwise stated. It must have a specific orientation or be constructed and operated in a specific orientation, so it should not be construed as a limitation on the scope of protection of the present invention: the orientation words "inside and outside" refer to the inside and outside relative to the contour of each component itself.

For ease of description, spatially relative terms, such as "on", "over", "on the surface", "above", etc., may be used herein to describe what is shown in the figures. The spatial positional relationship of one device or feature shown to other devices or features. It should be understood that spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or features would then be oriented "below" or "over" the other devices or features under its device or structure". Thus, the exemplary term "above" can encompass both an orientation of "above" and "below." The device may also be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptions used herein interpreted accordingly.

In addition, it should be noted that the use of words such as "first" and "second" to define components is only for the convenience of distinguishing corresponding components. Unless otherwise stated, the above words have no special meaning and therefore cannot be understood to limit the scope of protection of the present invention.

Example 1

In this example, a U-type optical fiber-based molybdenum disulfide-gold film sandwich optical fiber SPR biosensor for detecting human immunoglobulin IgG is prepared, that is, the antigen to be detected is human immunoglobulin IgG, and the detected antibody is goat antibody Human immunoglobulin.

As shown in Figure 1, an optical fiber SPR biosensor, the sensor adopts a sensing structure based on U-shaped optical fiber molybdenum disulfide-gold film sandwich, including 30-40 cm U-shaped multimode fiber, U-shaped multimode fiber The middle curved part is the sensing area, the length of the sensing area is 20~30mm, the surface of the optical fiber in the sensing area is fixed with the molybdenum disulfide coating 3 by electrostatic self-assembly, and the thickness of the molybdenum disulfide coating is 0.65~13nm. The surface of the molybdenum sulfide coating is plated with gold film 4, and the thickness of the gold film layer is 40-55 nm. The surface of the gold film is solidified with an antibody-goat anti-human immunoglobulin 5 film through dopamine. The antigen to be detected is human immunoglobulin. During the detection process, the antibody- The goat anti-human immunoglobulin is combined with the antigen-human immunoglobulin 6, so that the surface of the antigen-human immunoglobulin is immobilized on the antibody-goat anti-human immunoglobulin film.

The sensing system formed by the above-mentioned U-shaped optical fiber-based molybdenum disulfide-gold film sandwich optical fiber SPR biosensor is shown in Figure 2, including the optical fiber SPR biosensor A, and the system takes the multimode optical fiber as the optical path, that is, the multimode optical fiber is the optical path D. The input end of the optical fiber SPR biosensor A is connected to a broadband light source B whose spectrum is in the visible light band, and the output end is connected to a broadband spectrometer C. The broadband spectrometer C is connected to the computer E through a data interface, and the optical fiber SPR biosensor A is placed in the container to be detected. In this embodiment, the container to be detected is a beaker F, and the optical fiber SPR biosensor A is placed in the solution to be detected.

To prepare the above-mentioned optical fiber SPR biosensor method, the steps are as follows:

(a) Optical fiber pretreatment: take a 35cm multimode optical fiber, remove the 25mm long coating layer in the middle of the optical fiber, remove the impurities attached to the surface of the optical fiber in the sensing area, form the sensing area, bend the optical fiber to form a U shape, and use the alcohol lamp outside The flame heats the bent part to make the shape fixed, and the curvature radius of the U-shaped fiber is checked by controlling the bending degree;

(b) Preparation of molybdenum disulfide coating: The bent part of the U-shaped optical fiber was immersed in a piranha solution (a mixed solution of 95-98% concentrated sulfuric acid with a mass fraction of 7:3 and a mass fraction of 30% hydrogen peroxide) ) for 1 hour, take out and soak in 100mg/ml PDDA aqueous solution for 1 hour, and then soak in 0.1mg/ml molybdenum disulfide nanosheet absolute ethanol dispersion for 3 hours; take PDDA solution as the connection between the optical fiber and molybdenum disulfide The connecting medium, PDDA is positively charged, and molybdenum disulfide nanosheets are negatively charged. The molybdenum disulfide is fixed on the surface of the optical fiber by electrostatic adsorption, and the thickness of the molybdenum disulfide coating is 10 nm;

(c) deposition of gold film layer: the gold film was deposited by a magnetron sputtering apparatus, and the thickness of the gold film was controlled to be 50 nm by adjusting the discharge time to be 3 minutes and the current magnitude to be 7 mA;

(d) Antibody immobilization: Immerse the bent part of the U-shaped optical fiber in 5 mg/ml dopamine solution (solvent is 2% tris buffer) for half an hour. Dopamine polymerizes in water to form polydopamine on the surface of the gold film in the sensing area. After taking it out, it was dried in an incubator at 60 °C for half an hour, and then the sensor sensing area was immersed in 0.1 mg/ml antibody solution for 12 hours; polydopamine was used as the connecting medium between the gold membrane and the immobilized antibody, and the antibody was immobilized on the gold membrane. surface;

(f) Detection of antigens

At a temperature of 25 °C, the U-shaped optical fiber-molybdenum disulfide-gold film sandwich structure SPR biosensor was immersed in IgG solution, and the resonance wavelength was shifted according to the specific binding between the antibody and the antigen to realize the detection of the antigen. The amount of wavelength shift is obtained by the amount of wavelength shift caused by the specific adsorption between the actual antigen-antibody.

The invention prepared above is based on the refraction of the U-shaped fiber-molybdenum disulfide-gold film sandwich structure SPR biosensor, the U-shaped fiber-based gold film fiber SPR biosensor and the U-shaped fiber-based gold film molybdenum disulfide fiber SPR biosensor Rate sensing characteristic test:

Among them, the gold-coated fiber SPR biosensor of U-shaped fiber is shown in Figure 3. Multimode fiber is used, and the U-shaped multimode fiber core 1 is coated with a gold film 4 with a thickness of 50nm on the surface of the outer layer 2; U-shaped fiber- The optical fiber SPR biosensor of gold film-molybdenum disulfide is shown in Figure 4, using multimode fiber, U-shaped multimode fiber core 1 outer layer 2 surface is sequentially coated with gold film 4 and molybdenum disulfide coating 3 from the inside to the outside.

In order to study the refractive index sensing performance of the sensor after the molybdenum disulfide coating and the gold-plated film are sequentially fixed on the surface of the multimode optical fiber from the inside to the outside, the above sensor is connected to the sensing system with the multimode optical fiber as the optical path, The input end uses a deuterium-halogen lamp with a wavelength range of 215nm to 2500nm as a light source, and an ocean optical spectrometer is used to detect the resonance spectrum, and then the sensor is immersed in an ethanol solution with a refractive index variation range of 1.3314-1.3623. The resonance spectrum is shown in Figure 5 As shown, the resonance wavelength shifts to the right as the refractive index increases. The sensitivity of the sensor can be expressed as the ratio of the shift Δλ _p of the resonance peak to the change _Δna of the refractive index of the sample to be measured, namely:

After testing, the refractive index sensitivity of the U-shaped optical fiber gold film optical fiber SPR biosensor is 3887.6nm/RIU; the refractive index sensitivity of the U-shaped optical fiber-gold film-molybdenum disulfide optical fiber SPR biosensor is 4946.8 nm/RIU; the present invention The optical fiber SPR biosensor is based on the U-shaped optical fiber-molybdenum disulfide-gold film sandwich structure, and its refractive index sensitivity fitting curve is shown in Figure 6. According to the slope of the fitting curve, the optical fiber SPR of the present invention can be obtained. The refractive index sensitivity of the biosensor is 6184.4 nm/RIU.

The optical fiber SPR biosensor of the present invention is based on a U-shaped optical fiber-molybdenum disulfide-gold film sandwich structure, and its resonance wavelength changes with time in IgG solutions with different concentrations as shown in Figure 7, and the resonance wavelength shifts with the IgG solution. The change of concentration is shown in Fig. 8, and the linear fitting curve of the amount of resonance wavelength shift in the range of IgG concentration of 5-20 μg/ml is shown in Fig. 9 .

It is obvious that the U-shaped fiber-based molybdenum disulfide-gold film sandwich fiber SPR biosensor of the present invention has higher sensitivity than general sensors.

The invention mainly utilizes the molybdenum disulfide-gold film sandwich structure to enhance the surface electric field strength to improve the detection sensitivity of the sensor. The molybdenum disulfide coating is immobilized on the surface of the multimode fiber by electrostatic self-assembly. Molybdenum disulfide is used to promote the absorption of light energy, and the surface electric field is enhanced to improve the sensitivity. Using dopamine-immobilized antibodies to detect antigens can better reduce the detection limit. , the specific binding between antibody and antigen causes resonance wavelength shift, according to the ratio of biological analyte concentration and resonance wavelength shift to achieve high-sensitivity measurement of antigen, through the calculation of the limit test performance index LOD to achieve the lowest detection limit measurement.

The above technical solutions illustrate the technical ideas of the present invention, and cannot limit the protection scope of the present invention. Any changes and modifications made to the above technical solutions according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention belong to the scope of the present invention. The protection scope of the technical solution of the present invention.

Claims (8)

1. The optical fiber SPR biosensor is characterized in that a sensing structure of a molybdenum disulfide-gold film interlayer based on a U-shaped optical fiber is adopted, the middle bending part of the U-shaped optical fiber is a sensing area, a molybdenum disulfide coating is coated on the surface of the sensing area optical fiber, a gold film layer is plated on the surface of the molybdenum disulfide coating, and an antibody is fixed on the surface of the gold film through dopamine.

2. The fiber SPR biosensor of claim 1, wherein said molybdenum disulfide coating is applied to the surface of said optical fiber by electrostatic self-assembly.

3. The optical fiber SPR biosensor of claim 1, wherein the length of said sensor optical fiber is 30-40 cm, and the length of said sensing area is 20-30 mm.

4. The optical fiber SPR biosensor of claim 1, wherein said molybdenum disulfide coating has a thickness of 0.65 to 13 nm.

5. The optical fiber SPR biosensor of claim 1, wherein the thickness of said gold film layer is 40-55 nm.

6. The fiber SPR biosensor of claim 1, wherein said molybdenum disulfide-gold film sandwich layer has a total thickness of 60 nm.

7. The fiber SPR biosensor of claim 1, wherein said molybdenum disulfide coating is 10nm and said gold film layer is 50nm thick.

8. The method of claim 1, wherein the method comprises the steps of:

(a) optical fiber pretreatment: taking a multimode optical fiber of 30-40 cm, taking down a coating layer of 20-30 mm in length in the middle of the optical fiber, removing impurities attached to the surface of the optical fiber in a sensing area to form the sensing area, bending the optical fiber to form a U shape, and heating the bent part by utilizing the outer flame of an alcohol lamp to fix the shape;

(b) preparing a molybdenum disulfide coating: soaking the bent part of the U-shaped optical fiber in a piranha solution for 0.5-1.5 hours, taking out the bent part of the U-shaped optical fiber, soaking the bent part of the U-shaped optical fiber in a PDDA aqueous solution of 10mg/ml-1g/ml for 0.5-1.5 hours, and then soaking the bent part of the U-shaped optical fiber in molybdenum disulfide nanosheet water or ethanol dispersion of 0.1 mg/ml-200 mg/ml for 3-12 hours; the method comprises the following steps of (1) taking a PDDA solution as a connecting medium between an optical fiber and molybdenum disulfide, enabling the PDDA to be positively charged and the molybdenum disulfide nanosheet to be negatively charged, and fixing the molybdenum disulfide on the surface of the optical fiber by an electrostatic adsorption method;

(c) and (3) deposition of a gold film layer: depositing a gold film by adopting a magnetron sputtering instrument, wherein the discharge time is 1.5-5 min, the current is 0-10 mA, and the thickness of the gold film is controlled by adjusting the discharge time and the current;

(d) and (3) fixing the antibody: immersing the bent part of the U-shaped optical fiber in 1 mg/ml-100 mg/ml dopamine solution for half an hour, carrying out polymerization reaction on dopamine in water to form polydopamine on the surface of a gold film in a sensing area, taking out the polydopamine, drying the polydopamine in a constant temperature box at 60 ℃ for half an hour, and then immersing the sensing area of the sensor in 0.01 mg/ml-1 mg/ml antibody solution for 12 hours; and poly-dopamine is used as a connecting medium for the gold film and the immobilized antibody, and the antibody is immobilized on the surface of the gold film.

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