An infrared biological detection system

Abstract

The present invention relates to the technical field of biosensing and detection, and particularly relates to an infrared biological detection system, which includes a femtosecond pulsed light source, a first converging lens, an optical fiber sensing part, a second converging lens, and a photodetector. The femtosecond pulsed light source emits femtosecond pulsed laser, and the femtosecond pulsed laser is coupled into one end of the optical fiber sensing part through the first converging lens. Infrared light is generated and emitted from the other end of the optical fiber sensing part, and the infrared light enters the photodetector after passing through the second converging lens. The optical fiber sensing part includes a first optical fiber, a tapered optical fiber, a second optical fiber, and a thin film layer. The two ends of the tapered optical fiber are respectively connected to the first optical fiber and the second optical fiber, and the thin film layer is disposed on the surface of the tapered optical fiber. In the present invention, a thin film layer is provided outside the tapered optical fiber, and mid-infrared light is transmitted at the interface between the tapered optical fiber and the thin film layer. There are many biological molecules actually participating in the interaction, which have a great influence on the characteristics of light propagation at the interface. Therefore, high-sensitivity detection of biological molecules can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of biosensing and detection, and particularly relates to an infrared biological detection system. Background Art

[0002] The characteristic absorption wavelengths of the molecular vibrations of many biomolecules or organic substances are in the infrared, especially in the mid-infrared band. The spectral technology in the infrared band plays an important role in the qualitative and quantitative analysis of biomolecules. On this basis, the spectral technology in the infrared band can also be extended to biomedical tissue imaging, material detection, mineral detection, environmental monitoring, etc.

[0003] Optical fiber sensors have the characteristics of small volume, high sensitivity, long transmission distance, etc. Utilizing the influence of biomolecules on the sensing characteristics of optical fibers to construct an optical fiber-based biological detection system is of great significance.

[0004] Generally speaking, in an optical fiber sensor, a continuous spectrum light source is used, and the continuous spectrum light source outputs continuous spectrum laser, and the continuous spectrum laser is coupled into the optical fiber sensor. Since the characteristic spectra of biomolecules are in the near-infrared waveguide, the light sources adopted by researchers are also mostly near-infrared light sources. Such a setting can indeed achieve the function of detecting biomolecules, but it also damages the activity of biomolecules and is limited in practical applications.

[0005] CN115096851A discloses a biosensor, which includes an input optical fiber, a sensing optical fiber, and an output optical fiber connected in sequence; the sensing optical fiber has a fully normal dispersion distribution, and the light source is a femtosecond pump pulse; a femtosecond laser is used to remove the core and cladding of the sensing optical fiber to form a microcavity; when sensing biomolecules, the biomolecules to be detected are in the microcavity; the change in the refractive index of the microcavity leads to the change of the interference spectrum, realizing biosensing. In this scheme, although mid-infrared biomolecule detection is achieved, the biomolecules are only arranged in the microcavity, and the microcavity has a small size, and the change in the optical path caused by the microcavity is small, resulting in insufficient sensitivity of this structure for detecting biomolecules. Summary of the Invention

[0006] To solve the above problems, the present invention provides an infrared biological detection system, which includes a femtosecond pulse light source, a first converging lens, an optical fiber sensing unit, a second converging lens, and a photodetector. The femtosecond pulse light source emits femtosecond pulse laser, and the femtosecond pulse laser is coupled into one end of the optical fiber sensing unit through the first converging lens. Infrared light is generated and emitted from the other end of the optical fiber sensing unit, and the infrared light enters the photodetector after passing through the second converging lens. The optical fiber sensing unit includes a first optical fiber, a tapered optical fiber, a second optical fiber, and a thin film layer. The two ends of the tapered optical fiber are respectively connected to the first optical fiber and the second optical fiber, and the thin film layer is disposed on the surface of the tapered optical fiber. In this way, the femtosecond pulse laser is coupled into the open end of the first optical fiber through the first converging lens, and infrared light is emitted from the open end of the second optical fiber. The infrared light enters the photodetector through the second converging lens. The photodetector realizes the spectral detection of the emitted light.

[0007] The core concept of the present invention is that the femtosecond pulse laser irradiates the tapered optical fiber, and the tapered optical fiber generates a nonlinear optical effect, and mid-infrared light propagates along the tapered optical fiber in the tapered optical fiber. Due to the small diameter of the tapered optical fiber, the mid-infrared light is easily leaked from the inside of the tapered optical fiber or coupled into the interface between the thin film layer and the tapered optical fiber and transmitted along the interface. In this way, there are two transmission paths: one is transmitted along the fiber core, and the other is transmitted along the above interface. The superposition between the two transmission paths forms an output spectrum that depends on the interface environment. In application, biological molecules are arranged on the thin film layer, the light propagation characteristics of the above interface are affected by the refractive index of the biological molecules on the thin film layer, and the biological molecules can cover the thin film layer in a large area, and the biological molecules have a great influence on the light propagation characteristics of the above interface. Therefore, the present invention can realize the detection of biological molecules with high sensitivity.

[0008] Furthermore, the diameter of the tapered optical fiber is less than 5 microns, so that more mid-infrared light of the tapered optical fiber can be coupled into the interface between the tapered optical fiber and the thin film layer, that is, a stronger light path is formed on the above interface, and the contrast when the light in the two light paths is superposed is increased.

[0009] Furthermore, the thickness of the thin film layer is less than 200 nanometers. Furthermore, the thickness of the thin film layer is less than 100 nanometers, so that the biological molecules outside the thin film layer can more affect the light transmission characteristics of the interface formed by the tapered optical fiber and the thin film layer, thereby realizing the detection of biological molecules with higher sensitivity.

[0010] Furthermore, the first optical fiber and the second optical fiber are single-mode optical fibers, and the femtosecond pulse laser is transmitted along the first optical fiber, and mid-infrared light is excited in the tapered optical fiber. The first optical fiber is a single-mode optical fiber, and the energy is more concentrated in the core region of the first optical fiber, and stronger mid-infrared light can be generated in the tapered optical fiber.

[0011] Furthermore, the thin film layer coats the tapered optical fiber. That is to say, not only is the thin film layer disposed on the upper surface of the tapered optical fiber, but the entire thin film layer covers the tapered optical fiber. In this way, the light coupled into the interface between the tapered optical fiber and the thin film layer is stronger, improving the detection resolution.

[0012] Furthermore, the thin film layer is located in the middle of the tapered optical fiber, and both ends of the thin film layer do not contact the first optical fiber and the second optical fiber. In particular, the thin film layer does not contact the first optical fiber. The distance between the thin film layer and the first optical fiber is greater than 4 microns.

[0013] Furthermore, the tapered optical fiber is made by tapering a sulfide optical fiber or a fluoride optical fiber.

[0014] Furthermore, the material of the thin film layer is a metal or a semiconductor.

[0015] Furthermore, the metal is a noble metal or aluminum.

[0016] Furthermore, the semiconductor is silicon.

[0017] Advantages of the present invention:

[0018] (1) The present invention applies a tapered optical fiber, and a thin film layer is disposed outside the tapered optical fiber, and mid-infrared light is transmitted at the interface between the tapered optical fiber and the thin film layer. There are many biomolecules actually participating in the action, which have a great influence on the optical propagation characteristics of the interface and a great influence on the final transmission spectrum. Therefore, highly sensitive biomolecule detection can be achieved.

[0019] (2) The present invention disposes the thin film layer in the middle of the tapered optical fiber, and both ends of the thin film layer do not contact the first optical fiber. The input femtosecond pulsed laser will not be coupled into the interface between the tapered optical fiber and the thin film layer. In this way, only the generated mid-infrared light acts on the biomolecules, avoiding damage to the biomolecules.

[0020] Combining the above effects, the present invention has good application prospects in the field of biological detection.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings. Description of the Drawings

[0022] Figure 1 is a schematic diagram of an infrared biological detection system.

[0023] Figure 2 is a schematic diagram of an optical fiber sensing part.

[0024] Figure 3 is a schematic diagram of the optical transmission of mid-infrared light in the optical fiber sensing part

[0025] In the figure: 1. Femtosecond pulse light source; 2. First converging lens; 3. Optical fiber sensing part; 4. Second converging lens; 5. Photodetector; 31. First optical fiber; 32. Tapered optical fiber; 33. Second optical fiber; 34. Thin film layer. Specific implementation mode

[0026] To make the objectives, technical solutions and advantages of the present application clearer and more understandable, the following takes examples with reference to the attached drawings and further elaborates on the present application in detail.

[0027] The present invention provides an infrared biological detection system, as Figure 1 shown, including a femtosecond pulse light source 1, a first converging lens 2, an optical fiber sensing part 3, a second converging lens, and a photodetector. The femtosecond pulse light source emits femtosecond pulse laser, and the femtosecond pulse laser is coupled into one end of the optical fiber sensing part through the first converging lens. Infrared light is generated and emitted from the other end of the optical fiber sensing part, and the infrared light enters the photodetector after passing through the second converging lens. As Figure 2 shown, the optical fiber sensing part 3 includes a first optical fiber 31, a tapered optical fiber 32, a second optical fiber 33, and a thin film layer 34. The two ends of the tapered optical fiber 32 are respectively connected to the first optical fiber 31 and the second optical fiber 33, and the thin film layer 34 is placed on the surface of the tapered optical fiber 32. The material of the tapered optical fiber 32 has a fully normal dispersion distribution. The tapered optical fiber 32 is made by tapering a sulfide optical fiber or a fluoride optical fiber, and the structure adopts a step-index optical fiber or a graded-index optical fiber to achieve self-phase modulation. In this way, the femtosecond pulse laser is coupled into the open end of the first optical fiber 31 through the first converging lens 2, and mid-infrared light is emitted from the open end of the second optical fiber 33. The mid-infrared light enters the photodetector 5 through the second converging lens 4. The photodetector 5 realizes the spectral detection of the emitted light.

[0028] The central wavelength of the femtosecond pulse laser emitted by the femtosecond pulse light source 1 is 4 micrometers - 6 micrometers, the frequency range is dozens of hertz, and the pulse width is 100 femtoseconds - 200 femtoseconds. The central wavelength of the femtosecond pulse laser is set in the nonlinear region of the tapered optical fiber 32. The femtosecond pulse laser is transmitted through the first optical fiber 31 and irradiates the tapered optical fiber 32, and mid-infrared light is excited in the tapered optical fiber 32. Due to the small diameter of the tapered optical fiber 32, the mid-infrared light easily leaks from the inside of the tapered optical fiber 32 or is coupled into the interface between the thin film layer 34 and the tapered optical fiber 32 and is transmitted along the interface. As Figure 3As shown, there are two transmission paths: one is along the core of the tapered fiber 32 (the first path), and the other is along the above-mentioned interface (the second path). The mid-infrared light is superimposed after passing through these two transmission paths to form an output spectrum that depends on the interface environment. In application, the biomolecules are arranged on the thin film layer 34, and the light propagation characteristics of the above-mentioned interface are affected by the refractive index of the biomolecules on the thin film layer 34. In the present invention, the biomolecules can cover the thin film layer 34 in a large area, and the influence of the biomolecules on the light propagation characteristics of the above-mentioned interface is great. Therefore, the present invention can detect biomolecules with high sensitivity.

[0029] Preferably, in the tapered region, the diameter of the tapered fiber 32 is less than 5 μm; more preferably, in the tapered region, the diameter of the tapered fiber 32 is less than 2 μm, so as to facilitate more mid-infrared light of the tapered fiber 32 to be coupled into the interface between the tapered fiber 32 and the thin film layer 34, that is, to form an optical path with a stronger light field on the above-mentioned interface, increase the contrast when the light in the two optical paths is superimposed, improve the resolution between the spectra, and finally improve the sensitivity of biomolecule detection.

[0030] Preferably, the thickness of the thin film layer 34 is less than 200 nm. Further, the thickness of the thin film layer 34 is less than 100 nm, so as to facilitate the biomolecules outside the thin film layer 34 to more affect the light transmission characteristics of the interface formed by the tapered fiber 32 and the thin film layer 34, thereby realizing higher-sensitivity biomolecule detection.

[0031] Preferably, the length of the thin film layer 34 is greater than 10 μm. When the light propagates along the two paths in Figure 3 the change in the refractive index of the biomolecules can more cause the optical path of the light transmitted at the interface, thereby more increasing the optical path difference between the two paths of light propagation and improving the sensitivity of biomolecule detection.

[0032] Preferably, the first optical fiber 31 and the second optical fiber 33 are single-mode optical fibers. The femtosecond pulsed laser is transmitted along the first optical fiber 31, and mid-infrared light is excited in the tapered fiber 32. The first optical fiber 31 is a single-mode optical fiber, and the energy is more concentrated in the core region of the first optical fiber 31, and stronger mid-infrared light can be generated in the tapered fiber 32. Preferably, the core diameters of the first optical fiber 31 and the second optical fiber 33 are both less than 9 μm.

[0033] Preferably, the thin film layer 34 covers the tapered fiber 32. That is to say, not only is the thin film layer 34 provided on the upper surface of the tapered fiber 32, but the entire thin film layer 34 covers the tapered fiber 32. In this way, the light coupled into the interface between the tapered fiber 32 and the thin film layer 34 is stronger, and the detection resolution is improved.

[0034] Preferably, the thin film layer 34 is located in the middle of the tapered fiber 32, and both ends of the thin film layer 34 do not contact the first optical fiber 31 and the second optical fiber 33. In particular, the thin film layer 34 does not contact the first optical fiber 31. The distance between the thin film layer 34 and the first optical fiber 31 is greater than 4 micrometers, so as to prevent the femtosecond pulsed laser transmitted in the first optical fiber 31 from coupling into the interface between the tapered fiber 32 and the thin film layer 34, causing damage to biomolecules.

[0035] In the present invention, the tapered fiber 32 is made by tapering a sulfide optical fiber or a fluoride optical fiber. The optical fiber sensing part 3 is prepared by the following method: First, the first optical fiber 31, the nonlinear optical fiber, and the second optical fiber 33 are fused; then, the nonlinear optical fiber region is burned with a hydrogen-oxygen flame and drawn into a taper. In addition, the optical fiber sensing part 3 can also be prepared by first burning the nonlinear optical fiber with a hydrogen-oxygen flame and drawing to form the tapered fiber 32, and then fusing the first optical fiber 31 and the second optical fiber 33 at both ends of the tapered fiber 32.

[0036] In the present invention, the material of the thin film layer 34 is a metal, such as a noble metal material or aluminum. Mid-infrared light is confined to propagate between the tapered fiber 33 and the metal, and the metal has a good confinement effect on mid-infrared light. Metal thin films, such as noble metal thin films and aluminum thin films, can be prepared by electron beam evaporation coating. Electron beam evaporation has a high energy density and can evaporate noble metals and aluminum. During preparation, the optical fiber sensing part 3 is fixed on the substrate in the electron beam evaporation chamber, and aluminum foil paper is used to cover the first optical fiber 31 and the second optical fiber 33, and the area where the first optical fiber 31, the second optical fiber 33 are fused with the tapered fiber 32. Then, the metal in the crucible is melted by applying an electron beam, and the surface of the tapered fiber 32 is coated. After one coating is completed, the optical fiber sensing part 3 is turned over, and the same method is used to coat again, so as to make the metal film cover the tapered fiber 32 more.

[0037] In addition, the material of the thin film layer 34 can also be a semiconductor material, such as silicon. The silicon thin film can also be prepared by electron beam evaporation. Through electron beam evaporation, an amorphous silicon thin film is deposited on the surface of the tapered fiber 32. In addition, the silicon thin film can also be prepared by chemical vapor deposition.

[0038] Furthermore, holes are provided in the thin film layer 34, and the holes penetrate through the thin film layer 34. For example, the holes penetrate through a noble metal thin film, an aluminum thin film, or a silicon thin film. The holes can be circular or other shapes. The shape of the holes is not limited. When the holes are circular, the diameter of the holes is less than 400 nanometers. When the holes are other shapes, they have similar dimensions. In application, biomolecules are not only placed on the surface of the thin film layer 34 but also disposed in the holes. The mid-infrared light at the interface between the tapered optical fiber 32 and the thin film layer 34 is coupled into the holes and propagates to the surface of the thin film layer 34, increasing the length of the interface path (the second path). Moreover, in the holes, the electromagnetic field is further confined, and its effective refractive index depends more severely on the refractive index of the biomolecules. When the concentration of the biomolecules changes, the optical path of the interface path (the second path) changes more, causing a greater change in the transmission spectrum, that is, a greater shift of the transmission peak. Therefore, highly sensitive detection of biomolecules can be achieved. It should be emphasized here that the role of the holes here is to increase the optical path of the interface path (the second path), rather than forming resonance of mid-infrared light in the holes.

[0039] In summary, the present invention provides a novel infrared biological detection system. A thin film layer 34 is provided outside the tapered optical fiber 32, and mid-infrared light is transmitted at the interface between the tapered optical fiber 32 and the thin film layer 34. A large number of biomolecules actually participate in the action, greatly affecting the optical propagation characteristics of the interface and the final transmission spectrum. Therefore, highly sensitive detection of biomolecules can be achieved.

[0040] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. An infrared biological detection system, comprising a femtosecond pulse light source, a first converging lens, an optical fiber sensing part, a second converging lens, and a photodetector. The femtosecond pulse light source emits femtosecond pulse laser, the femtosecond pulse laser is coupled into one end of the optical fiber sensing part through the first converging lens, infrared light is generated and emitted from the other end of the optical fiber sensing part, and the infrared light enters the photodetector after passing through the second converging lens. It is characterized in that, The optical fiber sensing part includes a first optical fiber, a tapered optical fiber, a second optical fiber, and a thin film layer. The tapered optical fiber is made by tapering a sulfide optical fiber or a fluoride optical fiber. The tapered optical fiber generates a nonlinear optical effect. The two ends of the tapered optical fiber are respectively connected to the first optical fiber and the second optical fiber. The thin film layer is disposed on the surface of the tapered optical fiber, and the thin film layer covers the tapered optical fiber. There are holes in the thin film layer, and the holes penetrate through the thin film layer. In application, biomolecules are not only disposed on the surface of the thin film layer but also in the holes.

2. The infrared biological detection system according to claim 1, characterized in that: The diameter of the tapered optical fiber is less than 5 microns.

3. The infrared biological detection system according to claim 1, characterized in that: The thickness of the thin film layer is less than 200 nanometers.

4. The infrared biological detection system according to claim 1, wherein: The first optical fiber and the second optical fiber are single-mode optical fibers.

5. The infrared biological detection system according to claim 1, wherein: The thin film layer is located in the middle of the tapered optical fiber, and the two ends of the thin film layer do not contact the first optical fiber and the second optical fiber.

6. The infrared biological detection system according to any one of claims 1-5, characterized in that: The material of the thin film layer is metal or semiconductor.

7. The infrared biological detection system according to claim 6, wherein: The metal is a noble metal or aluminum.

8. The infrared biological detection system according to claim 6, wherein: The semiconductor is silicon.

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