CN111060481A

CN111060481A - Nanometer microscopic imaging device based on coaxial double-waveguide optical fiber SPR (surface plasmon resonance)

Info

Publication number: CN111060481A
Application number: CN201911303389.6A
Authority: CN
Inventors: 苑立波; 纪竞凯
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2019-12-17
Filing date: 2019-12-17
Publication date: 2020-04-24

Abstract

The invention provides a coaxial double-waveguide fiber SPR (surface plasmon resonance) -based nano-micro imaging device. The method is characterized in that: the coaxial double-waveguide optical fiber laser comprises a coaxial double-waveguide optical fiber 1, a coaxial double-waveguide optical fiber connector 2, a camera 3, a computer 4, a light source 5 and an optical fiber 6. The surface plasmon resonance can be effectively restrained on the surface of a metal layer of the end face of the cone frustum of the optical fiber and is very sensitive to environmental changes, the annular core 1-1 of the coaxial double-waveguide optical fiber 1 is utilized to enable laser excited surface plasmons to interact with a sample, trailing brought by the surface plasmons after acting on the sample is eliminated, meanwhile, the middle core of the coaxial double-waveguide optical fiber 1 is used for collecting scattered light, and microscopic imaging with high signal-to-noise ratio and high resolution ratio is realized through processing of the computer 4. The invention uses special optical fiber, can effectively reduce cost, optimize structure, and realize portable high signal-to-noise ratio and high resolution micro-nano microscopic imaging.

Description

Nanometer microscopic imaging device based on coaxial double-waveguide optical fiber SPR (surface plasmon resonance)

(I) technical field

The invention relates to a coaxial double-waveguide fiber SPR (surface plasmon resonance) based nano microscopic imaging device, belonging to the field of optical fiber microscopic imaging.

(II) background of the invention

Microscopic imaging is the most common and effective tool in optical detection for scientific research. With conventional microscopes, the minimum distance between two objects that can be clearly resolved depends on the limits of the microscope. In order to better visualize the microscopic world, researchers have endeavored to develop various methods of improving resolution. The super-resolution imaging technology has also made a breakthrough, and typically represents Confocal Microscopy (Confocal Microscopy), stimulated emission Depletion Microscopy (STED), Photo-activated localization Microscopy (PALM), and so on. It should be noted that in all super-resolution imaging techniques herein, the optical path used is a far-field leakage radiation imaging system.

Fluorescence detection is an important tool in the field of biological science. Surface-tethered technologies are often used in clinical diagnostics and DNA analysis to capture antibodies, DNA oligomers or target molecules, etc. The resolution of a common fluorescence microscope is 200nm, and an ultrahigh-resolution fluorescence microscope can realize imaging of a structure smaller than 10nm, but all the imaging needs to perform fluorescence calibration on a sample, so that the properties of the sample such as activity and the like can be changed and the authenticity of the sample cannot be reflected. It is therefore important for optical microscopes to increase their resolution and achieve the elimination of fluorescent labels. Evanescent waves can be used as a source of microscope illumination, for example, evanescent waves generated by Total Internal Reflection (TIR) as proposed by In single-molecule imaging with objective detection using organic total temporal feedback contrast optics and by eye attenuation In total temporal feedback contrast using 1-space light can be used for light field surface imaging. The measurement by the TIR method is that the incident light is required to be more than the critical angle, an evanescent field is excited, the longitudinal penetration depth of the evanescent field is about 100nm, and the evanescent field is a local electromagnetic field. This localized electromagnetic field allows selective observation of biomolecules on the surface of the sample, a technique that is critical to the optical field of cell and molecular biology. TIR illumination can be used to selectively image the sample surface, minimizing the reduction of the bulk background signal and increasing the signal-to-noise ratio.

Many methods based on surface signal detection cannot collect fluorescence signals weakly bound to the surface. However, for many types of biological imaging experiments, detection of the sample bulk radiation signal can also provide a useful signal, thus requiring measurement of both the tightly bound molecular fluorescence signal and the bulk target molecular signal. In these cases, it is useful to selectively excite surface or bulk target molecules. The surface bound fluorescence signal measurement allows the bulk signal to be maximally not collected, thus eliminating the step of washing unbound fluorophores. TIR, however, has difficulty in obtaining electromagnetic fields with long evanescent depths and thus in detecting bulk phase signals. Fluorescence microscopy is a typical means of wide field illumination or volumetric imaging away from the surface of a glass substrate. Surface or bulk sample imaging can be achieved using Total Internal Reflection Fluorescence Microscopy (TIRFM) and fluorescence microscopy, respectively, however, simultaneous concurrent bursts of both imaging are difficult to achieve. The simultaneous switching between the two imaging techniques requires precise mechanical alignment, which is difficult to perform in practice.

The surface wave microscope solves the problems, and the surface wave microscope uses surface waves, mainly surface plasmon resonance of metal and air cross section, as an illumination light source, and realizes high-sensitivity imaging of a sample close to the surface of a metal film layer by using the characteristics of strong locality of surface propagation and very sensitivity to disturbance at an interface. Chinese patent CN 103837499A proposes a micro-area spectrum measuring device based on broadband surface plasma waves, which mainly uses a high numerical aperture microscope objective and broadband radial polarized light or radial polarized white light to build up a spectrum measuring device. High spatial resolution can be achieved on the basis of this arrangement. Chinese patent CN 105628655 a proposes an optical microscope based on surface plasmon resonance with high resolution and without fluorescent label, which excites plasmon surface resonance at a plasmon resonance sensing chip, thereby obtaining high spatial resolution. The above-mentioned main microscopic techniques have great limitations in practical applications, and have the following problems:

1. the signal-to-noise ratio is poor. When evanescent wave microscopic imaging is carried out, because evanescent waves of an excitation field and surface waves scattered by a sample interfere with each other, strong tailing is formed on one side of the sample along the excitation direction, the tailing length is equal to the attenuation length of the evanescent waves along the surface, tailing signals and sample scattering signals are leaked down and collected by an imaging system, and the imaging signal-to-noise ratio is remarkably reduced.

2. The spatial resolution is poor. Also due to the smear, when an evanescent wave imaging system images an actual sample with a boundary, a fringe-like smear is generated at the boundary, and the resolution of the evanescent wave imaging system is remarkably reduced.

3. The time resolution is poor. In order to improve the resolution of an evanescent wave imaging system developed in recent years, multiple multi-angle acquisition of images is often required, and the imaging trailing is eliminated by using an algorithm to improve the resolution. The problems that each microscopic image needs a lot of time and the time resolution is poor, and real-time observation cannot be carried out are brought.

Chinese patent CN 109239020 a proposes a surface wave imaging system based on rotation illumination, which eliminates the tail caused by the surface wave acting on the sample by the galvanometer scanning system, and improves the signal-to-noise ratio and resolution of the surface wave microscopic imaging, but the used devices are of many kinds and have large volume, resulting in heavy weight and inconvenience.

The single optical fiber imaging technology adopts a single multimode optical fiber for imaging, the optical fiber is an imaging device and an image transmission device, a scene in a section of view field range of the optical fiber can be transmitted to the other end at one time without adding a scanning device and an imaging lens, and the single optical fiber imaging technology belongs to a wide-field optical fiber imaging technology. Through the development of the last 10 years, the single fiber imaging technology has made great progress in the aspects of imaging mechanism, imaging quality, application research and the like, but has many defects in the aspects of imaging speed and resolution.

The invention discloses a coaxial double-waveguide fiber SPR (surface plasmon resonance) based nano-micro imaging device. The defects of low signal-to-noise ratio, poor time and space resolution and high cost of the traditional surface wave imaging microscope are overcome. The coaxial double-waveguide optical fiber is adopted, surface plasma resonance waves are used for obtaining scattering signals with high resolution and high signal-to-noise ratio, and meanwhile, an optical fiber imaging mode is adopted for obtaining images; the excitation of SPR and the acquisition of image signals are finished by using the same optical fiber, so that a high-quality image can be obtained, and portable microscopic detection imaging can be realized.

Disclosure of the invention

The invention aims to provide a surface enhanced nano-micro imaging device which has simple and compact structure, good stability, low manufacturing cost and easy assembly, can realize the real-time observation of a non-fixed surface sample and obtain the coaxial double waveguide fiber SPR nano-micro imaging device based on high signal-to-noise ratio and high resolution imaging of the surface sample.

The invention is realized by the following steps:

based on coaxial double waveguide fiber SPR nanometer microscopic imaging device, its characteristics are: the coaxial double-waveguide optical fiber laser comprises a coaxial double-waveguide optical fiber 1, a coaxial double-waveguide optical fiber connector 2, a camera 3, a computer 4, a light source 5 and an optical fiber 6. In the composition: a beam of light emitted by a light source 5 passes through a coaxial double-wave optical fiber connector 2 through an optical fiber 6 and is injected into an annular core 1-1 of a coaxial double-wave optical fiber 1, and the micro-machined optical fiber end enables the light to have a specific angle with a metal layer on the conical end surface of the optical fiber, wherein the angle can be obtained under known parameters; laser forms a bundle of light illumination samples with specific incidence angles through the annular core 1-1 of the coaxial double-waveguide fiber 1, and the light illumination samples have large enough wave vectors to effectively excite plasmons existing in a metal layer of the end face of the cone frustum of the fiber; when the surface plasmon propagates through a sample, scattered signal light and surface tailing are emitted, the laser is incident from the annular core 1-1 of the coaxial double-waveguide fiber 1, and the surface plasmon is excited by 360 degrees at the same time, so that the surface tailing can be effectively eliminated; scattered light is collected by the middle core 1-2 of the coaxial double waveguide fiber 1 connected with the camera 3, forms an interference pattern with the other light of the light source on the camera 3, and the assignment and the phase of the image are extracted from the fiber by the computer 4 by using an off-axis digital holographic algorithm and are restored on the computer, so that high-resolution and contrast surface wave microscopic imaging can be obtained.

The annular core 1-1 of the coaxial double-waveguide optical fiber 1 is an optical fiber which is provided with an annular waveguide which is symmetrical along the axis and a fiber core with a large core diameter in the middle. As shown in FIG. 2, 1-1 is the annular core of the coaxial double-waveguide fiber, and 1-2 is the intermediate core of the coaxial double-waveguide fiber. The intermediate core has a large diameter, scatters signal light, and contains an optical field of image information. Information including intensity distribution, phase distribution, light beam wave front and the like is input into a computer 4 through a camera 3 and is processed and transformed to obtain an image.

The imaging mode of the coaxial double waveguide fiber SPR nano microscopic imaging device uses the principle of single multimode fiber imaging. The Imaging principle of a Single Multimode Fiber is described in detail in the document "Scanner-Free and Wide-field endoscopic Imaging by Using a Single Multimode Optical Fiber", as shown in fig. 7, a laser emitted by a laser splits light into two parts, the transmitted light is reflected by a mirror and coupled with the Fiber through a mirror BS2, then the other end of the Fiber is a plane to be measured OP to illuminate a target object, then the light collected by the Fiber returns to an IP and then enters a camera to be combined with the light which is split by B1 and reflected into the camera through BS3 to form an interference image on the camera. And extracting the assignment and the phase of the image from the optical fiber by using an off-axis digital holographic algorithm, and restoring the image on a computer.

The imaging mode based on the coaxial double-waveguide fiber SPR nano microscopic imaging device is optimized and improved on the basis of single multimode fiber imaging, the coaxial double-waveguide fiber is adopted to replace a complex light path in a graph (7), a light source 5 divides the light into two beams through an optical fiber 6, one beam of light enters an annular core 1-2 of the coaxial double-waveguide fiber 1 through a coaxial double-waveguide fiber connector 2, an SPR illumination sample is converged and excited at the other end of the coaxial double-waveguide fiber, scattered light passes through a middle core 1-1 of the coaxial double-waveguide fiber 1, the coaxial double-waveguide fiber connector forms an interference image on a camera 6 through the optical fiber 6 and the other beam of light of the light source 5, and assignment and phase of the image are extracted from the fiber by using an off-axis digital holographic algorithm to restore the image on a computer.

The metal layer of the optical fiber cone round table end face totally reflects light on the optical fiber cone round table end face and the surface of the metal film to form evanescent waves to enter into the light-dispersing medium, and certain plasma waves exist in the metal medium film. The two waves resonate when they meet. As shown in FIG. 4, the incident wavelength was chosen to be 635nm, and SPR was excited using a Kretschmann configuration, with no significant change in the S-wave, with reference to the change in reflected wave energy from SPR as a function of incident angle. However, the P wave changes obviously, a resonance peak exists at a specific angle, and when the ambient refractive index is increased from 1.0 to 1.1, the resonance peak of SPR shifts, thereby showing the sensing capability of the wave.

The system uses the coaxial double-waveguide fiber 1, obtains a relation graph of SPR reflected wave energy changing along with a resonance angle according to parameters of a metal layer of a configured fiber cone truncated cone end surface and a known environment refractive index, obtains an optimal incident angle, and obtains the conical fiber end coaxial double-waveguide fiber 1 with a required angle theta through a micro-processing mode shown in a graph (2).

The coaxial double-waveguide fiber SPR-based nano-microscopic imaging device is characterized in that a light source is transmitted by an annular core 1-1 of a coaxial double-waveguide fiber 1 with an angle theta, laser can excite plasma resonance waves 360 degrees around the center as shown in a figure (5), so that trailing images obtained by a plasma resonance enhancement effect in a single direction are eliminated, and images with high signal-to-noise ratio and high resolution are finally obtained.

In the coaxial double-waveguide fiber SPR-based nano-microscopic imaging device, scattered light enters a camera 3 from a middle core 1-2 of the coaxial double-waveguide fiber and is processed by a computer 4 to obtain an image with high resolution and high signal-to-noise ratio.

The coaxial double-waveguide fiber SPR-based nano microscopic imaging device can realize portable microscopic imaging.

(IV) description of the drawings

Fig. 1 is a schematic structural diagram of a coaxial double-waveguide fiber SPR-based nano-micro imaging device, which includes a coaxial double-waveguide fiber 1, a coaxial double-waveguide fiber connector 2, a camera 3, a computer 4 and a light source 5.

FIG. 2 is a cross-sectional view of a coaxial double-waveguide fiber, with 1-1 being the annular core of the coaxial double-waveguide fiber and 1-2 being the intermediate core of the coaxial double-waveguide fiber.

FIG. 3 is a drawing of a polishing process of the annular core 1-1 of the coaxial double waveguide optical fiber 1, starting from (a), with the optical fiber and the polishing disk rotating simultaneously to ensure symmetry of the processed optical fiber; (b) is a diagram of the grinding process; (c) is an effect diagram after finishing grinding; (d) is a defined fiber grind angle.

FIG. 4 is a graph of plasmon resonance reflection energy versus incident wave angle.

Fig. 5 is a schematic diagram of 360-degree excitation of surface plasmons.

Fig. 6 is a schematic diagram of a coaxial dual-waveguide optical fiber cone, 8 is a multilayer dielectric film, and 7 is a pellet to be tested.

FIG. 7 is a schematic diagram of a single multimode fiber imaging.

(V) detailed description of the preferred embodiments

The invention is further illustrated with reference to the following figures and specific examples.

Fig. 1 is a schematic structural diagram of a coaxial double-waveguide fiber SPR-based nano-micro imaging device according to the present invention, and the structure includes a coaxial double-waveguide fiber 1, a coaxial double-fiber optical fiber connector 2, a camera 3, a computer 4 and a light source 5. The end face structure of the coaxial double waveguide fiber 1 is shown in fig. 2.

Example 1:

firstly, manufacturing a metal layer on the end face of the cone frustum of the optical fiber, and plating a 45nm silver film on the surface of a glass plate. The object to be measured is placed in water or a specific liquid, so that the refractive index of the environment is fixed. From the parameters of the known plasma chip, the refractive index n of the prism₀Dielectric constant e of silver film ═ 1.56₂-13.4+1.4i, refractive index n of ambient liquid_eAs shown in fig. 4, the relationship between the reflectance of the light wave and the incident wave angle was obtained as 1.1, and it was found that the resonance effect was the best when the incident angle was 43 degrees under this condition.

The coaxial double waveguide fiber 1 was polished in the manner shown in fig. 3 with 43 degrees as the angle θ, to obtain a taper end with an angle θ.

In the ring core optical fiber SPR surface enhanced nano microscope stage, light emitted by a light source 5 passes through a bundle of optical fibers 6, penetrates through a coaxial double-wave optical fiber connector 2, and is injected into a ring core 1-1 of a coaxial double-wave optical fiber 1, and the micro-machined optical fiber end enables the light to have a specific angle with a metal layer on the end surface of a cone frustum of the optical fiber, wherein the angle can be obtained under known parameters; laser forms a bundle of light illumination samples with specific incidence angles through the annular core 1-1 of the coaxial double-waveguide fiber 1, and the light illumination samples have large enough wave vectors to effectively excite plasmons existing in a metal layer of the end face of the cone frustum of the fiber; when the surface plasmon propagates through a sample, scattered signal light and surface tailing are emitted, the laser is incident from the annular core 1-1 of the coaxial double-waveguide fiber 1, and the surface plasmon is excited by 360 degrees at the same time, so that the surface tailing can be effectively eliminated; scattered light is collected by the middle core 1-2 of the coaxial double waveguide fiber 1 connected with the camera 3, forms an interference pattern with the other light of the light source on the camera 3, and the assignment and the phase of the image are extracted from the fiber by the computer 4 by using an off-axis digital holographic algorithm and are restored on the computer, so that high-resolution and contrast surface wave microscopic imaging can be obtained.

Claims

1. Based on coaxial double waveguide fiber SPR nanometer microscopic imaging device, its characteristics are: the coaxial double-waveguide optical fiber laser comprises a coaxial double-waveguide optical fiber 1, a coaxial double-waveguide optical fiber connector 2, a camera 3, a computer 4, a light source 5 and an optical fiber 6.

In the composition: a beam of light emitted by a light source 5 passes through a coaxial double-wave optical fiber connector 2 through an optical fiber 6 and is injected into an annular core 1-1 of a coaxial double-wave optical fiber 1, and the micro-machined optical fiber end enables the light to have a specific angle with a metal layer on the conical end surface of the optical fiber, wherein the angle can be obtained under known parameters; laser forms a bundle of light illumination samples with specific incidence angles through the annular core 1-1 of the coaxial double-waveguide fiber 1, and the light illumination samples have large enough wave vectors to effectively excite plasmons existing in a metal layer of the end face of the cone frustum of the fiber; when the surface plasmon propagates through a sample, scattered signal light and surface tailing are emitted, the laser is incident from the annular core 1-1 of the coaxial double-waveguide fiber 1, and the surface plasmon is excited by 360 degrees at the same time, so that the surface tailing can be effectively eliminated; scattered light is collected by the middle core 1-2 of the coaxial double waveguide fiber 1 connected with the camera 3, forms an interference pattern with the other light of the light source on the camera 3, and the assignment and the phase of the image are extracted from the fiber by the computer 4 by using an off-axis digital holographic algorithm and are restored on the computer, so that high-resolution and contrast surface wave microscopic imaging can be obtained.

2. The SPR based nano-micro imaging apparatus based on coaxial double waveguide fiber according to claim 1, wherein the coaxial double waveguide fiber 1 is an optical fiber having an axially symmetric ring waveguide and a large core in the middle.

3. The SPR nano-microscopic imaging device based on the coaxial double-waveguide fiber according to claim 1, wherein the annular core 1-1 of the coaxial double-waveguide fiber 1 is used for transmitting incident light, and 360-degree surface plasmons can be simultaneously excited, so that the surface trailing of imaging caused by the surface plasmons excited in a single direction is eliminated; backward scattered light is collected by the annular core 1-2 of the coaxial double-waveguide fiber 1, and an image with high signal-to-noise ratio and high resolution is obtained by adopting a fiber imaging technology.