CN115755372A

CN115755372A - Transparent film applied to super-resolution imaging

Info

Publication number: CN115755372A
Application number: CN202211416442.5A
Authority: CN
Inventors: 叶永红; 杨松林; 相仲博
Original assignee: Nanjing Normal University
Current assignee: Nanjing Normal University
Priority date: 2022-11-12
Filing date: 2022-11-12
Publication date: 2023-03-07

Abstract

The invention relates to a transparent film applied to super-resolution imaging, which specifically comprises the following steps: step 1, preparing a photoresist cylinder on a quartz substrate by using a photoetching process; step 2, carrying out thermal reflow treatment on the photoresist cylindrical structure to manufacture a plano-convex lens; step 3, uniformly coating PDMS (polydimethylsiloxane) on the upper surface of the plano-convex lens, and removing the PDMS film to form a film with a spherical cavity structure; and 4, dripping the high-refractive-index liquid into the cavity structure obtained in the step 3, and covering the cavity structure on the sample to be measured. The technical scheme is that a film with a low refractive index and a spherical concave cavity structure is prepared, high-refractive-index liquid is filled in the film and covers a sample, and the film is placed under an optical microscope for imaging. Therefore, the Abbe diffraction limit is broken through, the resolving power of the traditional optical microscope is greatly improved, and super-resolution imaging with accurate positioning, convenient movement and no damage to a sample is realized.

Description

Transparent film applied to super-resolution imaging

Technical Field

The invention relates to a film, in particular to a transparent film applied to super-resolution imaging, and belongs to the technical field of optical microscopic imaging.

Background

The traditional optical microscope belongs to the field of far-field imaging, the resolution performance of the traditional optical microscope is limited by the diffraction limit, and details of a sample with the size smaller than half of the working wavelength are difficult to distinguish. The existence of diffraction limit causes that the traditional optical microscopy technology cannot meet the observation requirement of the field of life science and electronic technology on microstructures, so that the breakthrough of diffraction limit and the acquisition of super-resolution imaging are always the hot research subjects in the field of photonics. Electron microscopy and scanning probe microscopy developed in the last century have resolution capabilities on the nanometer scale, but these techniques do not allow for the observation of samples of living organisms. Methods such as a fluorescence super-resolution microscopy, a Fourier laminated microscopy and the like developed in recent years have great influence on a biological optical imaging technology, and the fluorescence super-resolution microscopy also obtains the Nobel prize in 2014. The fluorescence super-resolution microscopy realizes super-resolution imaging by carrying out special fluorescence labeling on a sample and using a special excitation light source. The Fourier laminated microscopic imaging technology acquires corresponding low-resolution images by changing the illumination direction of a sample, and performs phase restoration and aperture synthesis in a frequency domain to realize high-spatial resolution imaging.

However, the above techniques still have certain limitations and disadvantages. For example, the fluorescent marker has an influence on the sample, noise interference occurs in image reconstruction, and the method has a slow imaging speed and cannot directly observe the sample. Researchers have therefore been exploring and developing new label-free, wide-field illuminated optical super-resolution microscopy imaging techniques. In recent years, researchers have found that micro-scale lenses have special optical properties, and photon nano-jets formed by focusing electromagnetic waves have light intensity far higher than that of the irradiated waves and lateral full width at half maximum of subwavelength. The sample is imaged (real image or virtual image) through spherical and non-spherical microlenses placed on the surface of the sample, and the image formed by the microlenses is subjected to secondary imaging through an optical microscope, so that super-resolution imaging of the sample is realized. When the low-refractive-index microspheres are used for imaging, the microspheres are randomly dropped on the surface of a sample, and the microspheres are semi-immersed in liquid to enhance the super-resolution imaging capability of the microspheres, but the evaporation of the liquid can cause dynamic changes of the resolution and the magnification of the microspheres. This limitation can be avoided by completely immersing the high refractive microspheres in a liquid, but this approach does not allow accurate positioning of the microspheres in the region of interest of the sample. In order to solve this problem, some researchers assemble the microsphere and the probe and then move the microsphere for imaging, but the whole imaging system is complicated and inconvenient to operate.

In addition, researchers have also fabricated microlenses by different methods and processes, such as hot embossing, photoresist hot reflow, crystal growth methods, and the like. The microlens can be accurately positioned only in an area to be observed on the sample by manufacturing the solid immersion lens on the sample, but the microlens prepared by the method cannot move on the surface of the sample and can damage the sample. The movable microlens film is made to move on the surface of the sample and accurately locate at any area needing to be observed, however, the current microlens film is difficult to be in close contact with the sample (the gap between the sample and the film is less than one illumination wavelength), so that the microlens film is difficult to obtain high-resolution imaging. In addition, movable and super-resolution imaging can be realized by embedding barium titanate microspheres in the colloid film, but the imaging performance of the spherical lens is seriously influenced by the aberration of the spherical lens, and the field of view of the spherical lens is far smaller than that of the plano-convex micro lens. Therefore, a new solution to solve the above technical problems is urgently needed.

Disclosure of Invention

The invention provides a transparent film applied to super-resolution imaging, aiming at the problems in the prior art, and the technical scheme is that the super-resolution imaging with accurate positioning, convenient movement and no damage to a sample is realized by preparing a film with a low refractive index and a spherical cavity structure, filling high-refractive index liquid into the film and covering the film on the sample.

In order to achieve the above object, the invention provides a transparent film for super-resolution imaging, which comprises the following steps:

step 1, preparing a photoresist cylinder on a quartz substrate by using a photoetching process;

step 2, carrying out thermal reflow treatment on the photoresist cylindrical structure to manufacture a plano-convex lens;

step 3, uniformly coating PDMS on the upper surface of the plano-convex lens, and removing the PDMS film to form a film with a spherical cavity structure;

and 4, dripping high-refractive-index liquid into the cavity structure obtained in the step 3, and covering the cavity structure on the sample to be detected.

The step 1 is as follows: uniformly coating positive AZ4903 photoresist on a quartz substrate, controlling the thickness of the photoresist to be 10 mu m by the rotating speed of a photoresist homogenizer, and baking for 5 minutes at 80 ℃. And finally, carrying out mask exposure on the photoresist, and developing to obtain cylindrical structures with different aspect ratios.

The step 2 is as follows: and (3) transferring the quartz substrate with the photoresist cylinder prepared by the photoetching process in the step (1) to a hot plate, and carrying out photoresist thermal reflux treatment to form the plano-convex lens.

The step 3 is as follows: mixing and uniformly stirring the PDMS preculture and the curing agent according to the mass ratio of 10: 1, standing to remove bubbles, pouring onto the plano-convex lens obtained in the step 2, spin-coating PDMS, transferring to a hot plate to cure the PDMS, and removing the PDMS film to obtain the film with the spherical cavity structures with different aspect ratios.

The step 4 is as follows: dropping a certain volume of high refractive index liquid on the PDMS film, filling the high refractive index liquid into the cavity structure to form a plano-convex lens structure, covering the film on the sample, and imaging under an optical microscope.

As a modification of the invention, in step 4, the cavity structure of the film is filled with the high refractive index liquid and covered on the sample, the sample is in direct contact with the high refractive index liquid, and the film is covered on the high refractive index liquid.

As an improvement of the invention, the refractive index of the high refractive index liquid is in the range of 1.7-1.8, and PDMS is used as the material of the film with the spherical cavity structure. The refractive index of the high-refractive-index liquid filled in the spherical cavity structure is higher than that of the PDMS film, so that a plano-convex lens with the relative refractive index of 1.20-1.28 and the aspect ratio of 0.25-0.5 can be formed.

Compared with the prior art, the method has the advantages that the plano-convex lens structure is obtained through the thermal reflux treatment of the photoresist, and the imaging film with the high-precision spherical concave cavity structure is further prepared. And filling high-refractive-index liquid between the imaging film and the sample to form a plano-convex lens, and enabling the sample to be in close contact with the imaging film, so that super-resolution imaging is realized and a larger field of view is possessed. Meanwhile, the refractive index of the PDMS film is lower than that of the filled high-refractive-index liquid, so that the imaging effect can be further improved. In addition, the transparent film applied to super-resolution imaging provided by the invention has the capability of accurate positioning, convenient movement and no damage to a sample.

Drawings

FIG. 1 is a schematic diagram of the process for preparing a transparent thin film for super-resolution imaging according to the present invention;

FIG. 2 is a schematic diagram of an imaging system of the present invention for a transparent film for super-resolution imaging;

FIG. 3 is a schematic view of example 2 of the transparent film of the present invention applied to super-resolution imaging;

fig. 4 is a schematic view of example 3 of the transparent film applied to super-resolution imaging of the present invention.

In the figure: 1. objective lens, 2, PDMS film 3, high refractive index liquid, 4, sample.

Detailed Description

For the purpose of promoting an understanding of the present invention, reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Example 1: referring to fig. 1, a transparent film applied to super-resolution imaging specifically includes the following steps:

the step 1 is as follows: ultrasonically cleaning a quartz substrate in an acetone solution, uniformly coating positive AZ4903 photoresist after blow-drying by using a nitrogen gun, controlling the thickness of the photoresist to be 10 mu m by controlling the rotating speed of a photoresist homogenizer, then transferring a quartz plate uniformly coated with the photoresist to a hot plate, baking for 5 minutes at 80 ℃, finally performing mask photoetching on the photoresist, developing for 5 minutes, and preparing photoresist cylinders with different aspect ratios on the quartz plate.

The step 2 is as follows: and (2) transferring the quartz plate with the photoresist cylinder prepared by the photoetching process in the step (1) to a hot plate, baking for 2 hours at 200 ℃ for thermal reflux treatment, melting the photoresist at high temperature, and forming the plano-convex lens under the action of surface tension.

The step 3 is as follows: and (3) pouring PDMS onto the plano-convex lens obtained in the step (2), spin-coating PDMS to control the thickness of the PDMS to be 35um, transferring the PDMS to a hot plate, baking the PDMS for 1 hour at 90 ℃, curing the PDMS, and removing the PDMS film to obtain films with different aspect ratio spherical cavity structures.

The step 4 is as follows: dropping a certain volume of high-refractive-index liquid (the components are diiodomethane and sulfur, the refractive index is 1.79 at the wavelength of 540 nm) on the PDMS film, filling the high-refractive-index liquid into the concave cavity structure to form a plano-convex lens with the relative refractive index of 1.28, covering the film on a sample, and placing the sample under an optical microscope for imaging.

Example 2:

an illumination wavelength λ of 540nm was used and a numerical aperture NA of 0.9 was used with a microscope objective. The diameter of the bottom edge of the cavity structure of the film is 20 micrometers, the depth of the cavity structure of the film is 10 micrometers, and the cavity structure of the film is made of PDMS; the refractive index of the high refractive index liquid is 1.79; the sample to be tested is a blue-ray disc with the line width of 200nm and the groove of 100 nm.

The imaging effect of the transparent film applied to super-resolution imaging is schematically shown in fig. 3. As can be seen in FIG. 3, the film clearly resolved the periodic structures on the Blu-ray disc surface, which had exceeded the diffraction limit, but the structures were not resolved by optical microscopy alone under the same objective lens.

Example 3:

the illumination wavelength λ was 540nm and the numerical aperture NA was 0.9 using a microscope objective [1 ]. The diameter of the bottom edge of the cavity structure of the film is 20um, the depth is 10um, and the material is PDMS; the refractive index of the high refractive index liquid is 1.79; the sample to be detected is a triangular metal aluminum lattice with a detailed structure of 130 nm.

The imaging effect of the transparent film applied to super-resolution imaging is schematically shown in fig. 4. As can be seen from fig. 4, the micrometer scale imaging film can clearly resolve the detailed structure of the two triangular metal aluminum lattices.

It should be noted that the above-mentioned embodiments are not intended to limit the scope of the present invention, and all equivalent modifications and substitutions based on the above-mentioned technical solutions are within the scope of the present invention as defined in the claims.

Claims

1. A transparent film applied to super-resolution imaging is characterized by comprising the following steps:

and 4, dripping the high-refractive-index liquid into the cavity structure obtained in the step 3, and covering the cavity structure on the sample to be measured.

2. The transparent film for super-resolution imaging according to claim 1, wherein the step 4 is as follows: dropping a certain volume of high refractive index liquid on the PDMS film, filling the high refractive index liquid into the cavity structure, covering the film on the sample, and imaging under an optical microscope.

3. The transparent film for super-resolution imaging according to claim 2, comprising a film with spherical cavity structure and a high refractive index liquid, wherein the cavity structure of the film is filled with the high refractive index liquid and covered on the sample, the sample and the high refractive index liquid are in direct contact, and the film is covered on the high refractive index liquid.

4. The transparent film for super-resolution imaging of claim 3, wherein the refractive index of the high refractive index liquid is in the range of 1.7-1.8, and the material of the film with spherical cavity structure is PDMS. The refractive index of the high-refractive-index liquid filled in the spherical cavity structure is higher than that of the PDMS film, so that a plano-convex lens with the relative refractive index of 1.20-1.28 and the aspect ratio of 0.25-0.5 can be formed.