An on-chip plasmon scattering microscope based on one-dimensional photonic crystals

Abstract

The invention discloses an on-chip plasma scattering microscope based on one-dimensional photonic crystal, which belongs to the field of imaging and detection of small particle weak signals by surface waves, and includes: an image plane detector, an imaging tube lens, an air objective lens, a gold film, a one-dimensional photonic crystal, a scattering layer, and an LED light source. Refractive index matching oil is dripped between the gold film and the one-dimensional photonic crystal, and between the photonic crystal and the scattering layer for adhesion. After the light beam emitted by the LED light source passes through the scattering layer, the light beam is scattered to various angles. After filtering and screening by the one-dimensional photonic crystal in momentum space, the surface plasmons of the interface between the gold film and the air can be excited in all directions, and the nano-sized particles placed on the gold film can be illuminated. The scattered light of the particles is collected by the air objective lens placed above. The invention greatly improves the interaction between light and nano-particles, increases the scattering signal intensity of the particles, and improves the imaging quality at the same time, and can image and detect nano-particles with very small scattering signals.

Description

Technical Field

[0001] The invention relates to the field of imaging and detecting small particle weak signals by surface waves, and in particular to an on-chip plasma scattering microscope based on one-dimensional photonic crystals. Background Art

[0002] Imaging and detecting individual nanoparticles using optical label-free methods is essential for environmental monitoring, understanding chemical reaction mechanisms, and studying biological processes. Surface plasmon resonance microscopy has become a popular label-free detection technique due to its exceptional sensitivity to tiny signals. Surface plasmon is an evanescent field that can greatly enhance the interaction between light and nanoparticles. Therefore, surface plasmons can be used to develop highly sensitive label-free imaging methods, such as surface plasmon resonance microscopy, which has been used to image and detect weak signal objects such as single cells, subcellular organelles, viruses, nanoparticles, exosomes, etc. due to its extremely high sensitivity. However, surface plasmon resonance microscopy has certain limitations, and the problems it has are:

[0003] (1) Its spatial resolution is very poor, which is caused by the interference between the reflected wave and the scattered wave. There is a parabolic tail of the order of micrometers along the illumination direction. In addition, due to the presence of laser speckle, the imaging quality is deteriorated. Therefore, the surface plasmon resonance microscope has poor imaging resolution and imaging quality.

[0004] (2) Surface plasmon resonance microscopy requires complex optical devices, such as a high numerical aperture oil-immersion objective for exciting surface plasmons, various collimating lenses, polarizers and half-wave plates, and precise optical path adjustment, such as the need to precisely adjust the angle of the incident light to excite surface plasmons. These have limited the widespread use of surface plasmon resonance microscopy.

[0005] (3) Surface plasmon resonance microscopy has a limited imaging field of view. The traditional oil-immersion objective excitation method makes it have a small imaging field of view (on the order of micrometers by micrometers), which limits its imaging and detection capabilities over a large area. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the above-mentioned surface plasmon resonance microscope, and propose an on-chip plasma scattering microscope based on one-dimensional photonic crystals for label-free imaging and sensing of single nanoparticles. The on-chip plasma scattering microscope greatly simplifies the setting of the traditional surface plasmon resonance microscope by using one-dimensional photonic crystals to excite surface plasmons, and is simple to operate without optical adjustment. In addition, the use of LED light source has no laser speckle, and only the scattered light of the particles is collected without interference tailing, which improves the imaging resolution and can have a large imaging field of view of the order of centimeters by centimeters. The on-chip plasma scattering microscope realizes the imaging and detection of particles of tens of nanometers, such as the hygroscopic process of 50 nm sodium chloride aerosol and the chemical reaction process of perovskite nanocrystals with a side length of about 10 nm. It has the characteristics of label-free, high sensitivity, large field of view, high imaging quality, simple device, and no need for optical path adjustment.

[0007] The technical solution for achieving the above-mentioned purpose of the present invention is as follows: an on-chip plasma scattering microscope based on a one-dimensional photonic crystal, comprising: an image plane detector, an imaging tube lens, an air objective lens, a gold film, a one-dimensional photonic crystal, a scattering layer, and a 660nm broadband LED light source, wherein the gold film, the one-dimensional photonic crystal, the scattering layer, and the 660nm broadband LED light source are stacked in sequence from top to bottom to form a compact planar optical device for exciting surface plasmons, wherein refractive index matching oil is dripped between the gold film and the one-dimensional photonic crystal, and between the photonic crystal and the scattering layer for adhesion. The low-coherence light emitted by the LED light source is scattered in all directions after passing through the scattering layer, and then is incident on the one-dimensional photonic crystal. The filtering characteristics of the one-dimensional photonic crystal in momentum space are used to screen the outgoing light with an angle within the surface plasmon excitation angle range, and excite the surface plasmons at the interface between the gold film and the air, thereby achieving omnidirectional surface plasmon illumination of small particles in the azimuthal direction. The scattered light of the small particles is then collected by the air objective lens, passed through the imaging tube lens, and finally imaged on the image plane detector.

[0008] Furthermore, the one-dimensional photonic crystal is composed of SiO2 dielectric films with a refractive index of 1.46 and a thickness of 110 nm and Si3N4 dielectric films with a refractive index of 2.45 and a thickness of 75 nm, which are alternately chemically vapor deposited on a 0.17 mm cover glass, with a period number of 15.

[0009] The present invention places a gold film on a one-dimensional photonic crystal, excites surface plasmons at the interface between the gold film and air by adjusting the energy band structure of the one-dimensional photonic crystal, and irradiates the sample placed on the gold film. Compared with a dark field microscope based on a one-dimensional photonic crystal, the surface plasmon has a great field enhancement compared to the dark field illumination light, can improve the intensity of the interaction between light and matter, significantly improve the imaging contrast, and can image nanoparticles with a smaller scattering intensity (diameter); secondly, compared with a dark field microscope based on a one-dimensional photonic crystal, the gold film will further block the residual small-angle transmitted light emitted from the one-dimensional photonic crystal, thereby improving the dark field imaging effect. At the same time, the filtering range of the one-dimensional photonic crystal in the present invention in the momentum space is expanded to K / K0 greater than 1, and a higher NA objective lens can be used for dark field imaging compared with a dark field microscope based on a one-dimensional photonic crystal; finally, the present invention replaces the light source with a surface-emitting LED light source, which has lower cost, is more integrated, and reduces optical operations.

[0010] Compared with traditional optical methods (such as surface plasmon resonance microscopy) used to detect and image small particles, the present invention has the following benefits:

[0011] 1. The optical device is simple and does not require a surface plasmon excitation optical path, such as a high numerical aperture oil-immersion objective, polarizer, half-wave plate, imaging lens, etc.

[0012] 2. No optical operation is required, easy to use, no strict adjustment of the optical path is required to excite surface plasmons, and can be used in combination with traditional commercial microscopes without optical path adjustment.

[0013] 3. Large field of view imaging. In this device, the imaging field of view is determined by the illumination area of ​​the gold film surface (up to centimeters by centimeters) and the numerical aperture of the air objective lens. An air objective lens with a small numerical aperture can be used to achieve large field of view imaging.

[0014] 4. Low cost of use. Based on pure optical detection methods, it uses less consumables. The processing of multi-layer dielectric films is simple and cheap. It can be used in combination with ordinary commercial microscopes and has low cost.

[0015] 5. The imaging effect is good. The use of LED light source with weak coherence avoids laser speckle and improves the imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of an on-chip plasma scattering microscope based on a one-dimensional photonic crystal according to the present invention;

[0017] Figure 2 The distribution diagram of the transmittance of one-dimensional photonic crystal and the reflectance of gold film;

[0018] Figure 3This is a graph showing the relationship between the scattering intensity and the polystyrene spheres with different diameters measured using an on-chip plasma scattering microscope;

[0019] Figure 4 This is a graph showing the change in scattering intensity during the moisture absorption process of 50 nm sodium chloride particles measured using an on-chip plasma scattering microscope;

[0020] Figure 5 This is the result of measuring 10 nm gold particles and perovskite with a side length of about 10 nm using the microscope.

[0021] Figure 1 In the figure, 1 is an image plane detector, 2 is an imaging tube lens, 3 is an air objective lens, 4 is a gold film, 5 is a one-dimensional photonic crystal, 6 is a scattering layer, and 7 is an LED light source. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0023] The present invention provides an on-chip plasma scattering microscope based on a one-dimensional photonic crystal, such as Figure 1 As shown, it is used to detect and image a single nanoparticle, including: an image plane detector 1, an imaging tube lens 2, an air objective lens 3, a gold film 4, a one-dimensional photonic crystal 5, a scattering layer 6, and an LED light source 7. The low-coherence light emitted by the LED light source 7 is randomly scattered in all directions after passing through the scattering layer 6, and then the one-dimensional photonic crystal 5 filters in momentum space, screens the outgoing light with an outgoing angle within the surface plasmon excitation angle range, excites the surface plasmon of the gold film 4 and the air interface, and realizes omnidirectional surface plasmon illumination of small particles. After that, the air objective lens 3 collects the scattered light of the small particles, passes through the imaging tube lens 2, and finally forms an image on the image plane detector 1. The LED light source 7 uses a 660nm broadband LED light source, and refractive index matching oil is dripped between the gold film 4 and the one-dimensional photonic crystal 5, and between the photonic crystal 5 and the scattering layer 6 for adhesion.

[0024] Among them, the 660nm broadband LED light source 7 emits a light beam with a divergence angle of about 30 degrees, which is incident on the scattering layer 6, is scattered in all directions, and has random polarization, and is incident on the one-dimensional photonic crystal 5. The filtering characteristics of the one-dimensional photonic crystal 5 in momentum space are used to screen the outgoing light with an outgoing angle within the surface plasmon excitation angle range, and has transverse magnetic field (TM) polarization. Then the outgoing light excites the surface plasmon of the gold film 4 and the air interface, and realizes omnidirectional surface plasmon illumination of small particles in the azimuthal direction. Then the air objective 3 collects the scattered light of the small particles, passes through the imaging tube lens 2, and finally forms an image on the image plane detector 1. Note that in addition to the scattered light of the small particles, the scattered light of the surface roughness of the gold film 4 will also be collected and imaged by the air objective lens, and the scattered light of the small particles will interfere with the scattered light of the rough surface, which is beneficial to the detection of weak signal small particles. The on-chip plasma scattering microscope was used to image and detect polystyrene spheres of various sizes (with a minimum diameter of 40 nm) and gold spheres (with a minimum diameter of 10 nm), as well as the changes in the scattering intensity of 50 nm sodium chloride aerosol during moisture absorption and the chemical reaction process of perovskite nanocrystals with a side length of approximately 10 nm.

[0025] Furthermore, the divergence angle of the 660 nm broadband LED light source 7 used is not limited, and the wavelength bandwidth is about 20 nm. The LED light source 7 is composed of multiple LED lamp beads through a rectangular scattering plate, has low temporal and spatial coherence, removes laser speckle, and improves imaging quality.

[0026] Furthermore, the scattering layer 6 scatters the light beam emitted by the LED light source 7 in all directions. The scattering layer 6 is made by spin coating titanium dioxide particles with a diameter of about 60 nm on an ordinary glass sheet. The spin coating thickness is about 2 μm. Then, the scattered light in all directions is incident on the one-dimensional photonic crystal 5.

[0027] Furthermore, the one-dimensional photonic crystal 5 is composed of a SiO2 dielectric film with a refractive index of 1.46 and a thickness of 110 nm and a Si3N4 dielectric film with a refractive index of 2.45 and a thickness of 75 nm, which are alternately chemically vapor deposited on a cover glass, and the number of cycles is 15. The function of the one-dimensional photonic crystal 5 is to screen the light at various angles emitted by the scattering layer 6, so that it is emitted near the surface plasmon excitation angle, and the emitted light has transverse magnetic field (TM) polarization, so as to realize omnidirectional surface plasmon illumination of small particles.

[0028] Furthermore, the gold film 4 is made by depositing 50 nm of gold on a clean cover glass using magnetron sputtering technology. The surface of the gold film 4 is not completely flat, and the ups and downs of the surface roughness will also scatter light. The gold film 4 can also be replaced by other metal films that can excite surface plasmons, including silver film, copper film, and aluminum film.

[0029] Furthermore, the scattered light of small particles placed on the surface of the gold film 4 is collected and imaged by the air objective lens 3, the imaging tube lens 2, and the image plane detector 1. Air objective lenses with different numerical apertures can be selected to achieve different imaging fields of view and resolutions.

[0030] The present invention images and detects various standard polystyrene spheres (with a minimum diameter of 30 nm) and gold particle spheres (with a diameter of 10 nm and 5 nm), and also images and detects the changes in the scattering intensity during the moisture absorption process of 50 nm sodium chloride aerosol and the chemical reaction process of perovskite nanocrystals with a side length of about 10 nm.

[0031] Reference Figure 2 As shown in FIG. 5 , after filtering in momentum space by the one-dimensional photonic crystal 5, the outgoing light has a transverse magnetic field component, and most of it is concentrated in the range of K / K0 (K is the wave vector of the outgoing light from 1DPC, and K0 is the wave vector of the light propagating freely in a vacuum) greater than 1 to excite the surface plasmons at the interface between the gold film and the air. The excitation angle is as follows: Figure 2 As shown in the reflection trough of the gold film 4, it is on the side of the transverse magnetic field component where K / K0 is slightly greater than 1.

[0032] Reference Figure 3 The figure shows the relationship between polystyrene beads of different diameters and scattering intensity measured using an on-chip plasma scattering microscope. A drop of alcohol solution of polystyrene beads of standard diameter is dropped on the gold film. After a period of spin coating, the particles are deposited on the surface of the gold film and then imaged. It can be found that when the particle diameter is small, the scattering intensity (the square of the scattered light field) is approximately proportional to the sixth power of the diameter; when the particle diameter is small, the scattering intensity mainly comes from the interference between the scattered light of the roughness of the gold film 4 surface and the scattered light of the particles, so the scattering intensity is approximately proportional to the cube of the particle diameter (the first term of the scattered light field), which makes it easy for the microscope to detect weak signals of small particles.

[0033] Reference Figure 4 As shown in the figure, the scattering intensity change results of 50 nm sodium chloride particles during moisture absorption were measured using an on-chip plasma scattering microscope. Figure 4(b) When the relative humidity is less than or equal to 75%, the scattering intensity of the particles changes slowly. When the relative humidity increases to 77%, the scattering intensity increases dramatically. This humidity is called the deliquescence point. The experimental hygroscopic curve is consistent with the theoretical model of the extended inorganic aerosol model, that is, Figure 4 The solid line of (b) is in good agreement with the Figure 4 Figure (a) shows the experimental imaging under different humidity conditions. It can be found that when the humidity becomes 77%, the scattering intensity changes significantly.

[0034] Reference Figure 5 As shown in FIG. 1 , the results of measuring 10 nm gold particles and perovskite with a side length of about 10 nm using the microscope. Use gold particles of standard diameter, dispose in an alcohol solution, drop a drop on the gold film, spin coat and let stand, and then use the microscope of the present invention to take an image, such as; similarly, C S PbI3 perovskite particles were deposited on a gold film, and then HCl and HI gases were introduced into the particles to image the three states of the particles, as shown in Figure 2. Figure 5 , it can be found that the perovskite particles undergo anion replacement process, namely C S PbI3 to C S PbCl3 turns into C S PbI3. Realizes the detection and imaging of small particles. Figure 5 Figures A and B in the figure are the results of imaging 10 nm gold particles, and the three images in Figure B are enlarged images of the relevant areas of Figure A; Figure 5 Figures C, D, and E are respectively S PbI3、C S PbI3 (with HCl vapor), C S Imaging results of PbI3 (passing HCl vapor and then HI vapor).

[0035] Parts of the present invention that are not described in detail belong to the well-known technology in the art.

Claims

1. An on-chip plasmon scattering microscope based on one-dimensional photonic crystals for detecting and imaging single nanoparticles, characterized in that: include: An image plane detector (1), an imaging tube lens (2), an air objective lens (3), a gold film (4), a one-dimensional photonic crystal (5), a scattering layer (6), and a 660nm broadband LED light source (7); wherein the gold film (4), the one-dimensional photonic crystal (5), the scattering layer (6), and the LED light source (7) are stacked in sequence from top to bottom to form a planar optical device for exciting surface plasmons, wherein refractive index matching oil is dropped between the gold film (4) and the one-dimensional photonic crystal (5), and between the one-dimensional photonic crystal (5) and the scattering layer (6) for adhesion; The 660nm broadband LED light source (7) emits a beam with a divergence angle of 30 degrees, which is incident on the scattering layer (6), scattered in various directions, and has random polarization, and is incident on the one-dimensional photonic crystal (5). The filtering characteristics of the one-dimensional photonic crystal (5) in momentum space are used to screen the outgoing light with an outgoing angle within the surface plasmon excitation angle range and with transverse magnetic field polarization. The outgoing light then excites the surface plasmon of the interface between the gold film (4) and the air, thereby achieving omnidirectional surface plasmon illumination of the nanoparticles in the azimuthal direction. The scattered light of the nanoparticles is then collected by the air objective lens (3), passes through the imaging tube lens (2), and finally forms an image on the image plane detector (1).

2. The on-chip plasma scattering microscope based on one-dimensional photonic crystal according to claim 1, characterized in that: The wavelength bandwidth of the used 660 nm LED light source (7) is 20 nm. The LED light source (7) is composed of a plurality of LED lamp beads connected through a rectangular scattering plate.

3. The on-chip plasma scattering microscope based on one-dimensional photonic crystal according to claim 1, characterized in that: The scattering layer (6) scatters the light beam emitted by the LED light source (7) in all directions. The scattering layer (6) is made by spin coating titanium dioxide particles with a diameter of about 60 nm on a glass sheet. The spin coating thickness is 2 μm. The scattered light in all directions is then incident on the one-dimensional photonic crystal (5).

4. The on-chip plasma scattering microscope based on one-dimensional photonic crystal according to claim 1, characterized in that: The one-dimensional photonic crystal (5) is composed of a SiO2 dielectric film with a refractive index of 1.46 and a thickness of 110 nm and a Si3N4 dielectric film with a refractive index of 2.45 and a thickness of 75 nm, which are alternately chemically vapor deposited on a cover glass, and the number of periods is 15. The one-dimensional photonic crystal (5) is used to screen the light at various angles emitted by the scattering layer (6) so that it is emitted at the surface plasmon excitation angle, and the emitted light has a transverse magnetic field polarization, thereby realizing omnidirectional surface plasmon illumination of the nanoparticles.

5. The on-chip plasma scattering microscope based on one-dimensional photonic crystal according to claim 1, characterized in that: The gold film (4) was produced by magnetron sputtering to deposit 50 nm of gold on a clean cover glass and had a undulating surface roughness.

6. The on-chip plasma scattering microscope based on one-dimensional photonic crystal according to claim 1, characterized in that: The gold film (4) is replaced by a metal film capable of exciting surface plasmons, wherein the metal film includes a silver film, a copper film, and an aluminum film.

7. The on-chip plasma scattering microscope based on one-dimensional photonic crystal according to claim 1, characterized in that: The scattered light of the nanoparticles placed on the surface of the gold film (4) is collected and imaged by an air objective lens (3), an imaging tube lens (2), and an image plane detector (1). Air objective lenses (3) with different numerical apertures are selected to achieve different imaging fields of view and resolutions.

8. The on-chip plasma scattering microscope based on one-dimensional photonic crystal according to claim 5, characterized in that: The scattered light caused by the roughness of the surface of the gold film (4) is collected and imaged by the air objective lens (3), and the scattered light of the nanoparticles interferes with the scattered light of the rough surface, thereby realizing the detection of weak signal nanoparticles.

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