Preparation method of silk protein erasable optical platform

Abstract

The present invention relates to a method for preparing a silk protein erasable optical platform. The silkworm cocoons are degummed and dissolved to prepare a silk protein solution, which is coated on a hydrophobic silicon substrate, dried to obtain a silk protein film, one side of which is attached to an elastomer substrate, and fumigated in water vapor. After the end, a diffractive optical element is used as a template for room temperature imprinting, and the platform is peeled off after the humidity is restored to the ambient temperature, so as to obtain a silk protein erasable optical platform. The optical platform is exposed to water vapor again to erase the written microstructure, and then different diffractive optical element templates are used to implement imprinting to achieve rewriting of the microstructure. The scheme of the present invention is simple and fast, the conditions are mild and green, the raw materials are green and environmentally friendly, and the cost is low. The prepared optical platform can realize multi-channel imaging, multi-mode information switching, and multi-strategy information reuse, and has potential application prospects in the fields of intelligent display, high-security anti-counterfeiting and encryption.

Description

Technical Field

[0001] The invention belongs to the technical field of optical platforms, and in particular relates to a method for preparing a silk protein erasable optical platform. Background Art

[0002] At present, traditional optical devices can achieve a single function with high quality. However, with the rapid development of intelligent display, information anti-counterfeiting and sensing, the demand for new optical devices that can achieve multiple functions is growing. The optical multiplexing platform is a platform that integrates multiple information channels at the same time, which can display the optical information stored in each channel separately under specific external stimuli. Compared with traditional optical devices, optical multiplexing platforms with multiple information channels can achieve multiple functions at the same time, providing an opportunity to build a multifunctional integrated system that matches the high quality of traditional optical devices.

[0003] Metasurface is a typical optical multiplexing platform. By designing the size, shape and arrangement of surface structural units, multiple dimensions of light can be adjusted to achieve multifunctional integration. The document "Dynamic Bifunctional Metasurfaces for Holography and Color Display" discloses an optical multiplexing platform. By designing the orientation, size and arrangement period of elliptical metasurface structural units to control the spectrum and phase response of the metasurface, a metasurface that can dynamically "turn on" or "off" five holograms and multiple color-adjustable structural color patterns at two wavelengths is realized, that is, the phase adjustment of the incident light (different diffraction patterns appear when incident light of different wavelengths is irradiated) and the amplitude adjustment (color patterns of different colors) are simultaneously realized. However, metasurfaces are mainly processed by electron beam lithography, focused ion beam etching and other methods, which are complex and expensive. Once the preparation is completed, the micro-nano structure on the metasurface cannot be changed, that is, the encoded information cannot be changed, which limits the application scenarios of the metasurface optical platform. Therefore, it is of great application value to develop a multifunctional optical multiplexing platform with green and environmentally friendly materials, simple preparation process and repeatable encoding.

[0004] Micro-nano imprinting is a highly efficient, low-cost, and easily scalable lithographic technology that can be adapted to a variety of materials to give them micro-nano optical structures. The document "Rapid Nanoimprinting of Silk Fibroin Films for Biophotonic Applications" introduces two methods for imprinting silk fibroin films. One is to heat the template to 100°C and then apply a pressure of ~50 psi to the silk fibroin film at ambient humidity (~35%) for imprinting. The other is to spray a small amount of water on the silk fibroin film to reduce its glass transition temperature and then use the template to imprint at room temperature. However, both methods are uncontrollable, that is, they cannot achieve complex pattern imprinting and subsequent erasing, editing, and rewriting of patterns. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and provide a method for preparing a silk protein erasable optical platform. The method uses green, environmentally friendly, and widely available silk protein as a substrate, adopts a non-contact water vapor-assisted room temperature imprinting method, and performs patterned imprinting with the assistance of a customized hollow mask. The process is simple and the cost is low. The prepared optical platform can realize the cyclic erasing and rewriting of the imprinted pattern.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0007] A method for preparing a silk protein erasable optical platform comprises the following steps:

[0008] S1. Degumming silkworm cocoons to obtain degummed silk, dissolving the degummed silk and dialyzing it to prepare a silk fibroin solution, coating the silk fibroin solution on a hydrophobic treated silicon substrate, drying and peeling it off to obtain a silk fibroin film;

[0009] S2. attaching one side of the silk protein film of S1 to the elastomer substrate to obtain a silk protein film-elastomer substrate complex;

[0010] S3. Place the silk protein film-elastomer substrate complex in water vapor for fumigation, take it out after fumigation, place the diffractive optical element template on the silk protein film of the silk protein film-elastomer substrate complex, apply pressure for imprinting, and after the silk protein film returns to the ambient humidity, peel off the diffractive optical element template and the elastomer substrate to obtain a silk protein erasable optical platform printed with micro-nano structures.

[0011] Furthermore, in step S1, the degumming treatment method is: dissolving anhydrous sodium carbonate in boiling water to prepare a sodium carbonate solution with a concentration of 0.02M, then adding mulberry silkworm cocoon fragments to the solution and boiling for 30 minutes to remove sericin, followed by scrubbing with deionized water for 3-5 times, and drying to obtain degummed silk.

[0012] Furthermore, in step S1, the hydrophobic treatment method is: after cleaning the silicon substrate, put it into a vacuum drying oven, add 100 μL of trichloro(1H,1H,2H,2H-perfluorooctyl)silane, and let it stand for 20 minutes under a vacuum environment.

[0013] Furthermore, in step S1, the thickness of the silk protein film is 30-200 μm.

[0014] Furthermore, in step S2, the material of the elastomer substrate is polydimethylsiloxane, and the thickness is 0.5-2 mm.

[0015] Furthermore, in step S3, the water vapor fumigation temperature is 30-90° C. and the time is 5-60 seconds.

[0016] Further, in step S3, the pressure is 0.16-0.32 MPa.

[0017] Further, in step S3, the diffractive optical element template is a blazed grating, a holographic grating, a microlens, a two-dimensional photonic crystal, or an optical diffraction element with a stepped micro-nanostructured surface.

[0018] Further, the step S3 is replaced by the following method: attaching an elastomer mask with a hollow pattern on the side of the silk protein film of the silk protein film-elastic substrate complex, and then placing it in water vapor for fumigation, taking it out after the end, removing the elastomer mask, placing the diffractive optical element template on the silk protein film of the silk protein film-elastic substrate complex, applying pressure for imprinting, and after the silk protein film returns to the ambient humidity, peeling off the diffractive optical element template and the elastomer substrate to obtain a patterned silk protein erasable optical platform printed with micro-nano structures. The elastomer mask is prepared by using a CO2 laser cutting machine, setting the power to 10-40%, and cutting the polydimethylsiloxane elastomer according to the designed pattern.

[0019] The silk protein erasable optical platform prepared by the present invention can realize cyclic erasing and rewriting of the imprinted pattern, and the method is: the silk protein erasable optical platform is exposed to water vapor again to erase the written microstructure, and then different diffraction optical element templates are used to implement imprinting, thereby realizing rewriting of the microstructure.

[0020] In order to obtain a patterned optical platform, an elastomeric mask with a customized pattern can also be attached to the other side of the S2 film to form a three-layer structure of elastomeric substrate-film-elastomeric mask, so that the local area of ​​the film is unobstructed, and then the three-layer structure is placed in water vapor, and after the fumigation is stopped and the mask is removed, a diffractive optical element template is used to perform local embossing to obtain a patterned optical platform. On the basis of obtaining a patterned optical platform, in order to obtain a patterned optical platform with multiple microstructures integrated, another elastomeric mask with a customized pattern can be attached to the surface of the film to form a new three-layer structure, and the film side is fumigated with water vapor, and embossing is performed using different diffractive optical element templates to achieve the erasure and rewriting of local micro-nano structures.

[0021] To achieve double-sided micro-nano embossing, the film is peeled off from the elastic substrate, and the side printed with the micro-nano structure is attached to the elastic substrate to expose the other side of the film. The method of the present invention is used for embossing to obtain a double-sided embossed optical platform.

[0022] Beneficial effects of the present invention:

[0023] 1. The present invention provides an imprinting method that can achieve rapid and complex patterning at low temperature and low pressure. The method has a simple preparation process, can be quickly prepared on a large area, and the applied materials are green and environmentally friendly, with a wide source and excellent biocompatibility.

[0024] 2. The present invention repeatedly changes the glass transition temperature of the silk protein film through water vapor treatment, and can realize multiple editing of the micro-nano structure morphology on the surface of the silk protein film.

[0025] 3. The present invention can change the glass transition temperature of the micrometer-level region through droplet-shaped water mist processing, thereby achieving pixelated imprinting.

[0026] 4. The present invention achieves the modification of the micro-nano structure in a local area by assisting with a customized patterned hollow mask.

[0027] 5. The present invention can realize the function that the observed pattern information changes with the change of the observation angle by imprinting different areas on a single side of the silk protein film with grating templates of different periods.

[0028] 6. The present invention can realize the function that the observed pattern information changes with the change of the observation angle by imprinting grating templates with different periods on both sides of the silk protein film in directions perpendicular to each other.

[0029] 7. The present invention can store more complex coupling information by imprinting different types of optical elements on both sides of the silk protein film. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1Diffraction efficiency test results of the silk protein erasable optical platform prepared in Example 2 at different steam treatment temperatures and times;

[0031] Figure 2 Ratio of the residual diffraction efficiency to the diffraction efficiency before treatment of the silk protein erasable optical platform prepared in Example 2 after being treated at different steam treatment temperatures and times;

[0032] Figure 3 Diffraction efficiency and corresponding microscope images of the silk protein film prepared in Example 1 after being repeatedly imprinted 5 times with the same grating template;

[0033] Figure 4 Butterfly pattern obtained by imprinting the silk protein film prepared in Example 1 four times;

[0034] Figure 5 Photos of the silk protein optical platform obtained by imprinting the silk protein film prepared in Example 1 with four templates having different micro-nano structures under a laser confocal scanning microscope;

[0035] Figure 6 Optical photo of the silk protein optical platform with the pattern of "Fu" prepared in Example 7;

[0036] Figure 7 Optical photo of the silk protein optical platform with the pattern of "Libra" prepared in Example 8;

[0037] Figure 8 Optical photos of the optical platform prepared in Example 9 at different observation angles;

[0038] Fig. 9 Optical photos of the optical platform prepared in Example 10 at different observation angles;

[0039] Fig.10 Optical photos of the optical platform prepared in Example 11 at different observation angles;

[0040] Fig.11 Diffraction patterns of the optical platform obtained after double-sided imprinting and the optical platform obtained after double-sided rewriting in Example 12;

[0041] Fig.12 Optical photo of the optical platform prepared in Example 13. Detailed implementation manners

[0042] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited do not limit the present invention.

[0043] Example 1: Preparation of silk protein film

[0044] (1) Silk degumming: 21.2 g of anhydrous sodium carbonate was dissolved in 10 L of boiling water to prepare a sodium carbonate solution with a concentration of 0.02 M. Then 25 g of mulberry silkworm cocoon fragments were added to the solution and boiled for 30 min to remove sericin. The silk was then scrubbed with deionized water for 4 times and dried to obtain degummed silk.

[0045] (2) Silk dissolution: 5 g of degummed silk was added to 20 mL of 9.3 M lithium bromide solution, placed in a 60 °C oven, and the beaker was shaken every hour. After 4 hours, the solution was taken out to obtain the silk solution.

[0046] (3) Dialysis: Cut a section of dialysis bag with a molecular weight cutoff of 3500 kDa. Soak the dialysis bag in pure water for about 5 to 10 minutes, then pour the silk solution into the other end of the dialysis bag. After the solution is filled, clamp the other end with a dialysis clip. Place the bag in a beaker containing 5L of pure water and start dialysis. Change the water every 6 hours for a total of 10 times.

[0047] (4) taking out the silk fibroin solution in the dialysis bag and pouring it into a centrifuge tube, centrifuging it in a high-speed centrifuge and filtering it. The centrifuge parameters are: 11000r / min, each centrifugation for 20min, and centrifugation twice in total;

[0048] (5) placing the prepared silk fibroin solution into a centrifuge tube and storing it in a refrigerator at 4° C. for 7 to 10 days;

[0049] (6) placing a silicon wafer with a diameter of 5 cm and a thickness of 400 μm in a vacuum drying oven, adding trichloro(1H,1H,2H,2H-perfluorooctyl)silane, and standing for 20 minutes under a vacuum environment to obtain a hydrophobic silicon wafer;

[0050] (7) 6545 μL of a 6% silk fibroin solution was evenly coated on a silicon wafer, dried overnight in an environment with a relative humidity of 40%-50% and a temperature of 20-25°C, and then peeled off with a blade to obtain a silk fibroin film with a thickness of 50 μm.

[0051] Example 2: Effect of different water vapor treatment temperatures and times on embossing effects

[0052] The silk protein film prepared in Example 1 was attached to an elastomer substrate, and then fumigated at different water vapor treatment temperatures and times. After the fumigation, a diffractive optical element template was placed on the silk protein film, and pressure was applied for imprinting. After the film was restored to ambient humidity, the diffractive optical element template and the elastomer substrate were peeled off to obtain a silk protein optical platform printed with micro-nano structures. The diffraction efficiency of the silk protein optical platform under different treatment conditions was compared. The specific scheme is as follows:

[0053] The experiment was divided into four groups, each group had 13 silk protein films with a size of 1×1 cm. After being attached to an elastomer substrate, they were fumigated in a water bath at 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, respectively. The first group was fumigated for 5 seconds, the second group for 10 seconds, the third group for 20 seconds, and the fourth group for 30 seconds. Then they were taken out and quickly pressed on a blazed grating template with 600 grooves per millimeter. They were imprinted at a pressure of 0.16-0.32 MPa for 5-10 minutes. After the silk protein film returned to the ambient humidity, the diffractive optical element template and the elastomer substrate were peeled off to obtain a silk protein optical platform printed with micro-nano structures. All the silk protein optical platforms printed with micro-nano structures were irradiated with lasers in sequence, and the optical power of their positive first-order diffraction light was measured with an optical power meter. The value was compared with the optical power value of the incident laser to obtain the diffraction efficiency of the silk protein optical platform printed with micro-nano structures. The experimental results are shown in Figure 1 .

[0054] Figure 1 The diffraction efficiency test results of the silk protein erasable optical platform prepared at different water vapor treatment temperatures and times in Example 2. The diffraction efficiency is the ratio of the optical power value of the first-order diffracted light to the optical power of the incident light, which can be used to characterize the integrity of the micro-nano structure (Optomechanically Actuated Microcilia for Locally Reconfigurable Surfaces). Figure 1 It can be seen that under the same treatment time, the higher the water vapor treatment temperature, the higher the diffraction efficiency of the silk protein optical platform (this is because the micro-nano structure of the replicated grating template is more complete); it can also be seen that the longer the fumigation time of the silk film, the more it can replicate the complete grating structure under the water bath steam treatment at a lower temperature. For example, when treated for 30 seconds, the diffraction efficiency of the printed silk film can reach 40% after being treated in a 40°C water bath steam, but the 5-second treatment needs to be treated in a 70°C water bath steam to reach 40%.

[0055] Example 3: Effect of different water vapor treatment temperatures and times on erasing effects

[0056] The silk protein erasable optical platform of the present invention can realize the erasure of the imprinted pattern. The written microstructure can be erased by simply exposing the silk protein erasable optical platform to water vapor again. The effects of different water vapor treatment temperatures and times on the erasing effect are now investigated. The experimental scheme is as follows:

[0057] Take the silk protein erasable optical platform prepared in Example 2 (the water vapor treatment temperature during preparation is 45°C, and the fumigation time is 30s), divide it into four groups, each group has 9 pieces, and the size is 1×1cm. The first group, the second group, the third group and the fourth group are fumigated in a water bath at temperatures of 30°C, 35°C, 40°C and 45°C for 0s, 5s, 10s, 15s, 20s, 30s, 40s, 50s and 60s respectively. After the silk protein erasable optical platform returns to the ambient humidity, peel it off, and use an optical power meter to measure the diffraction efficiency after treatment. This value is compared with the diffraction efficiency before treatment to quantify the degree of erasure of the silk film micro-nano structure. The experimental results are shown in Figure 2 .

[0058] Figure 2 The ratio of the residual diffraction efficiency (Dr) of the silk protein erasable optical platform prepared in Example 2 after being treated with different water vapor treatment temperatures and times to the diffraction efficiency (Di) before treatment. It can be seen that in a water bath with a higher temperature, a relatively good erasing effect can be achieved with a very short treatment time. For example, in a water bath at 45°C, as long as the treatment time is less than 10s, the diffraction efficiency of the silk film drops to about 10% of the original (that is, the micro-nano structure on the silk film disappears), while in a water bath at 30°C, it takes 40s to achieve a similar erasing effect (the diffraction efficiency drops to about 10% of the original).

[0059] Example 4: Testing of Cyclic Imprinting and Erasing Performance

[0060] The silk protein film prepared in Example 1 was tested for cyclic printing and erasing performance, and the experimental method was as follows:

[0061] Step 1, attach a silk protein film with a size of 1×1 cm to an elastomer substrate, first fumigate it in a water bath at a temperature of 45°C for 30 seconds, take it out and press it on a blazed grating template with 600 grooves per millimeter, and print it at a pressure of 0.16-0.32 MPa for 5-10 minutes. After the silk protein film returns to the ambient humidity, peel it off, measure the optical power of the positive first-order diffraction light of the silk film with an optical power meter, and calculate its diffraction efficiency.

[0062] Step 2, put the silk protein film into a water bath at 45°C for fumigation for 30 seconds, take it out and emboss it under the same blazed grating template. At this time, the groove direction of the grating is perpendicular to that in step 1. After the humidity returns to the ambient temperature, peel it off and calculate the diffraction efficiency for the second time.

[0063] Step 3, repeat step 2 three times, and calculate the diffraction efficiency each time to characterize the imprinting performance.

[0064] Figure 3The diffraction efficiency and corresponding microscope image of the silk protein film prepared in Example 1 after being repeatedly stamped with the same grating template for 5 times. It can be seen that after the silk protein film prepared in Example 1 was stamped for 5 times, the diffraction efficiency did not decrease significantly, indicating that the silk film has good strength, so the micro-nano structure on the optical platform based on the silk protein film can be edited multiple times. The microscope image shows that after the fifth stamping, a relatively complete grating micro-nano structure can still be replicated.

[0065] Example 5: Cyclic patterned imprinting and erasing

[0066] Step 1, preparing a mask: 16g of polydimethylsiloxane (PDMS) matrix and 1.6g of curing agent were mixed evenly at a weight ratio of 10:1, poured into a culture dish with a diameter of 150mm, and cured at 60°C for 24 hours after vacuum removal of bubbles to obtain a PDMS film with a thickness of about 1mm. The mask was cut into a size of 4×4cm, and four different butterfly patterns were designed using drawing software, and then the four masks were cut out using a laser cutting machine, with the power set to 25%;

[0067] Step 2, first imprinting: Cut a piece of 4×4 cm in size from the silk protein film prepared in Example 1, stick one side of the silk protein film on a PDMS substrate of 5×5 cm, and then attach the first butterfly hollow-shaped mask to the other side of the silk protein film. Place the mask face up in a water bath at 45°C and fumigate for 30 seconds. After taking it out, quickly peel off the upper mask, and then press the surface of the silk protein film face down on the prepared optical element template. A blazed grating with 600 grooves per millimeter and a triangular cross-sectional shape is used here. Imprint for 5-10 minutes. After the silk protein film returns to the ambient humidity, peel off the silk protein film and the PDMS substrate together. Observe the silk protein film, you can see that the structure of the grating will be replicated in the butterfly area that is in contact with water vapor, showing angle-dependent rainbow colors on a macro scale, and the area blocked by the mask remains intact, take pictures and record;

[0068] Step 3, first erasing: stick the printed side of the silk protein film on the PDMS substrate, put them in a water bath at 45°C and fumigate for 30 seconds, take them out, and get the reset silk protein film. The micro-nano structure on the surface of the silk film is eliminated, and the angle-dependent rainbow color disappears on the macro scale.

[0069] Step 4, subsequent multiple rewriting: attach the second butterfly-shaped PDMS mask to the reset silk protein film obtained in step 3, repeat the operation of step 2, obtain the second posture of the rainbow-colored butterfly pattern with angle dependence, and repeat step 3 to erase the micro-nano structure. Attach the third butterfly-shaped PDMS mask to the reset silk film, repeat the operation of step 2, obtain the third posture of the rainbow-colored butterfly pattern with angle dependence, and repeat step 3 to erase the micro-nano structure. Attach the fourth butterfly-shaped PDMS mask to the reset silk film, repeat the operation of step 2, obtain the fourth posture of the rainbow-colored butterfly pattern with angle dependence, and repeat step 3 to erase the micro-nano structure to obtain the reset silk protein film.

[0070] Figure 4 The butterfly patterns are obtained by four stampings on the silk protein film prepared in Example 1. The directions indicated by the arrows are the patterns obtained by the first stamping, the second stamping, the third stamping, and the fourth stamping, respectively. It can be seen that four different butterfly patterns are patterned sequentially on a silk protein film.

[0071] Example 6: Continuous Imprinting with Optical Elements Having Different Micro-Nano Structures

[0072] Four templates with different micro-nano structures were prepared, namely: ① a holographic grating template with 1800 grooves per millimeter and a rectangular cross-section; ② a blazed grating template with 1200 grooves per millimeter and a triangular cross-section; ③ a stepped diffractive optical element template (whose reconstructed image is a snowflake shape); ④ a diffractive optical element template whose reconstructed pattern is a dot matrix shape.

[0073] Take the silk fibroin film prepared in Example 1, cut it into a size of 1×1 cm, attach it to the elastomeric substrate, first fumigate it in a water bath at 45 °C for 30 s, take it out and press it on Template ①, imprint it at a pressure of 0.16 - 0.32 MPa for 5 - 10 min. After the silk fibroin film returns to the ambient humidity, remove Template ①, observe and photograph it under a laser confocal scanning microscope; then place it in a water bath at 45 °C and fumigate it for 30 s, take it out and press it on Template ②, imprint it at a pressure of 0.16 - 0.32 MPa for 5 - 10 min. After the silk fibroin film returns to the ambient humidity, remove Template ②, observe and photograph it under a laser confocal scanning microscope; then place it in a water bath at 45 °C again and fumigate it for 30 s, take it out and press it on Template ③, imprint it at a pressure of 0.16 - 0.32 MPa for 5 - 10 min. After the silk fibroin film returns to the ambient humidity, remove Template ③, observe and photograph it under a laser confocal scanning microscope; then place it in a water bath at 45 °C again and fumigate it for 30 s, take it out and press it on Template ④, imprint it at a pressure of 0.16 - 0.32 MPa for 5 - 10 min. After the silk fibroin film returns to the ambient humidity, remove Template ④, observe and photograph it under a laser confocal scanning microscope.

[0074] Figure 5 Figure 4 shows the photographs of the silk fibroin optical platforms obtained by imprinting the silk fibroin film prepared in Example 1 with four templates having different micro - nano structures under a laser confocal scanning microscope. The directions indicated by the arrows are the photographs obtained by observing under the laser confocal scanning microscope after four imprints. It can be seen that the micro - nano structures of the silk fibroin optical platforms obtained after each imprint are consistent with the templates, indicating that the micro - nano structures on the silk film can be edited by different micro - nano structures.

[0075] Example 7: Achieving complex patterning using local rewriting

[0076] Step 1: Background imprinting: Cut out a piece of the silk fibroin film prepared in Example 1 with a size of 4×4 cm, attach one side to the PDMS substrate, put it into a water bath at 45 °C and fumigate it for 30 s. Take it out and quickly invert and press it on a blazed grating template with 600 grooves per millimeter. Imprint it at a pressure of 0.16 - 0.32 MPa for 5 - 10 min. After the silk fibroin film returns to the ambient humidity, peel it off, and the entire silk film shows angle - dependent iridescence.

[0077] Step 2: Customized mask: The same as Step 1 of Example 5, obtain a PDMS mask with the character "Fu" hollowed out.

[0078] Step 3: Rewrite patterning: Attach the hollowed-out PDMS mask of the word "Fu" to one side of the silk protein film, and the other side to the substrate. Put them into steam at 45°C for 30 seconds and then quickly take them out. Remove the upper "Fu" mask and press it upside down on another periodic blazed grating template (800 grooves per millimeter). The direction of the template here is the same as that in step 1 (parallel). After waiting for 5-10 minutes for the silk film to recover the ambient humidity, peel off the silk film to obtain a silk protein optical platform with a "Fu" pattern that is different from the background rainbow color.

[0079] Figure 6 This is an optical photograph of the silk protein optical platform with the "Fu" pattern prepared in Example 7, wherein: Figure 6 A is a photo of the silk protein optical platform. Figure 6 B is Figure 6 From the partial enlarged image of A, it can be seen that the rewritten "Fu" area has a different tone from the background area, and the boundary between the two is very narrow, only a few microns.

[0080] Example 8: Random pixelated imprinting using large droplet water mist

[0081] Step 1: Cut a piece of the silk protein film prepared in Example 1 into a size of 4×5 cm, attach one side of the film to the PDMS substrate, treat the other side with water mist generated by a humidifier for 5 seconds, and then quickly press it onto a blazed grating template. Press it at a pressure of 0.16-0.32 MPa for 5-10 minutes. After the silk film returns to the ambient humidity, peel it off. It is found that only the area where the droplets are randomly attached to the silk film undergoes glass transition, and the entire film appears as colorful stars.

[0082] Step 2: Attach the PDMS baffle with the "Libra" hollow on the silk film, treat it with water vapor, and then imprint it with a grating template. After the silk film returns to the ambient humidity, peel off the silk film to obtain a silk protein optical platform with the "Libra" pattern.

[0083] Figure 7 This is an optical photograph of the silk protein optical platform with a “Libra” pattern prepared in Example 8. A clear “Libra” pattern can be seen, indicating that the method of the present invention can achieve the imprinting of complex patterns.

[0084] Example 9: Imprinting different regions of a silk protein film with different templates

[0085] Step 1: preparing a mask: similar to step 1 of Example 5, four PDMS masks with hollowed-out shapes of “moon”, “grass”, “house”, and “sun” in different areas are prepared;

[0086] Step 2: Cut a piece of 4×5 cm from the silk protein film prepared in Example 1, attach one side to the PDMS substrate, cover the other side of the silk film with a "moon" shaped hollow mask, put them in a 45°C water bath and fumigate for 30 seconds, quickly remove the mask after taking them out, and imprint them upside down on a blazed grating template with 600 grooves per millimeter, imprint for 5-10 minutes at a pressure of 0.16-0.32MPa, and remove it after the silk film returns to the ambient humidity; then cover this silk film with a "grassland" shaped hollow mask On the silk film, the fumigation and peeling operations are repeated, and a blazed grating template with 800 grooves per millimeter is used for imprinting; then a "house" shaped hollow mask is covered on the silk film, the fumigation and peeling operations are repeated, and a blazed grating template with 900 grooves per millimeter is used for imprinting; finally, a "sun" shaped hollow mask is covered on the silk film, the fumigation and peeling operations are repeated, and a blazed grating template with 1200 grooves per millimeter is used for imprinting; in this embodiment, the four grating templates are placed in the same position (that is, the orientation of the grooves is the same) when they are imprinted separately, and a patterned optical platform is obtained.

[0087] Figure 8 Optical photographs of the optical platform prepared in Example 9 at different observation angles show that the observed pattern changes with the change of the observation angle.

[0088] Example 10: Imprinting grating templates with different periods on both sides of the silk film in parallel directions

[0089] Step 1: preparing a mask: same as step 1 of Example 5, obtaining two PDMS masks with hollow shapes of the letters "NJU" and "SILK" respectively;

[0090] Step 2: First side imprinting: Cut a piece of the silk protein film prepared in Example 1 into a size of 2×3 cm, stick one side on the PDMS substrate, and cover the other side with a PDMS mask with a hollow "NJU" shape. After fumigation, remove the upper mask, and then imprint with a blazed grating template with 600 grooves per millimeter;

[0091] Step 3: Second side imprinting: After peeling off the silk film obtained in step 2, attach the first side to the PDMS substrate, and then cover the top with a "SILK" shaped hollow PDMS mask. After fumigation, peel off the upper mask and imprint with a blazed grating template with 1200 grooves per millimeter. The placement direction of the template is the same as in step 2. After peeling it off, an optical platform is obtained.

[0092] Fig. 9The optical photographs of the optical platform prepared in Example 10 at different observation angles show that as the observation angle gradually increases from 0°, the pattern "NJU" is first observed, and its color gradually shifts to red. Then the observed pattern changes to "SILK", and as the observation angle continues to increase, the color gradually changes from blue to green and finally to red.

[0093] Example 11: Imprinting grating templates with the same period on both sides of the silk film in the vertical direction

[0094] Step 1: preparing a mask: same as step 1 of Example 5, obtaining two PDMS masks with hollow shapes of a chameleon and a double-stranded DNA;

[0095] Step 2: First side imprinting: Cut a piece of the silk protein film prepared in Example 1 into a size of 2×3 cm, stick one side on the PDMS substrate, and cover the other side with a chameleon-shaped hollow PDMS mask. After fumigation, peel off the upper mask, and then imprint with a blazed grating template with 600 grooves per millimeter, and peel it off after returning to ambient humidity;

[0096] Step 3: Second side imprinting: After peeling off the silk film obtained in step 2, attach the first side (i.e. the side with the chameleon imprinted) to the PDMS substrate, and then cover the top with a PDMS mask with a double-stranded DNA shape. After fumigation, peel off the upper mask and imprint with a blazed grating template with 600 grooves per millimeter. The template is placed perpendicular to step 2 and peeled off after returning to ambient humidity to obtain an optical platform.

[0097] Fig.10 The optical photographs of the optical platform prepared in Example 11 at different observation angles show that, as the observation angle changes from 0° to 90°, the observed pattern changes from chameleon to double-stranded DNA.

[0098] Example 12: Imprinting and rewriting on both sides of the silk film with different types of optical element templates

[0099] Step 1: First side imprinting: Cut a piece of the silk protein film prepared in Example 1 into a size of 1×1 cm, stick one side (this side is recorded as the second side) on the PDMS substrate, and the other side (this side is recorded as the first side) is fumigated and imprinted with a blazed grating template with 600 grooves per millimeter;

[0100] Step 2: Second side imprinting: After peeling off the silk film obtained in step 1, attach the first side to the PDMS substrate, and after fumigation, imprint the second side with a diffractive optical element whose holographic pattern is a snowflake. After returning to ambient humidity, peel off the silk film to obtain an optical platform with two sides imprinted.

[0101] Step 3: Rewriting the first side: After peeling off the silk film obtained in step 2, attach the second side to the PDMS substrate, and after fumigation, re-imprint the first side with a diffractive optical element with a reconstructed holographic pattern as a dot matrix;

[0102] Step 4: Rewriting the second side: After peeling off the silk film obtained in step 3, attach the first side to the PDMS substrate. After the second side is fumigated, it is re-embossed with a diffractive optical element with a reconstructed holographic pattern of a butterfly. After returning to ambient humidity, it is peeled off to obtain an optical platform with both sides rewritten.

[0103] Fig.11 The diffraction patterns of the optical platform obtained after double-sided imprinting and double-sided rewriting in Example 12, wherein: Fig.11 A is the diffraction pattern of the optical platform after printing on both sides. Fig.11 B is the diffraction pattern of the optical platform after rewriting on both sides. It can be seen that the method of the present invention can realize the imprinting and rewriting of different types of optical element templates on both sides of the silk film.

[0104] Example 13: Preparation of a multifunctional optical platform

[0105] Step 1, cutting a piece of the silk protein film prepared in Example 1 into a size of 2×2 cm, attaching one side of the piece to a PDMS substrate, and fumigating the other side, and then imprinting the piece with a blazed grating template having 600 grooves per millimeter;

[0106] Step 2, attaching a customized elastomeric mask with a hollow QR code pattern onto the silk film, and performing a fumigation operation again;

[0107] Step 3, attach the PDMS mask with the first corner block area of ​​the QR code hollowed out to the silk film, perform a fumigation operation, and then emboss with a blazed grating template with 800 grooves per millimeter; then attach the PDMS mask with the second and third corner block areas hollowed out to the silk film, perform a fumigation operation, and then emboss with a blazed grating template with 900 grooves per millimeter;

[0108] Step 4, after returning to ambient humidity, peel off the silk film from the substrate, and attach the printed side of the silk film to the substrate;

[0109] Step 5, after treating the silk film with large droplet water mist produced by a humidifier for 5 seconds, it is imprinted with a blazed grating template with 600 grooves per millimeter. The placement direction of the template here is perpendicular to that in step 1. After returning to ambient humidity, the silk film is peeled off to complete the preparation.

[0110] Fig.12 This is an optical photograph of the optical platform prepared in Example 13, wherein Fig.12 A is the side of the optical platform where the elastic mask with the hollow QR code pattern is attached. Fig.12 B is the other side. It can be seen that the method of the present invention can realize the embossing of complex patterns and customized patterns.

Claims

1. A method for preparing a silk protein erasable optical platform, characterized in that: The steps include: S1. Degumming silkworm cocoons to obtain degummed silk, dissolving the degummed silk and dialyzing it to prepare a silk fibroin solution, coating the silk fibroin solution on a hydrophobic treated silicon substrate, drying and peeling it off to obtain a silk fibroin film; S2. attaching one side of the silk protein film of S1 to the elastomer substrate to obtain a silk protein film-elastomer substrate complex; S3. placing the silk protein film-elastomeric substrate complex in water vapor for fumigation, taking it out after fumigation, placing a diffractive optical element template on the silk protein film of the silk protein film-elastomeric substrate complex, applying pressure for imprinting, and after the silk protein film returns to the ambient humidity, peeling off the diffractive optical element template and the elastomer substrate to obtain a silk protein erasable optical platform; In step S3, the water vapor fumigation temperature is 30-90° C. and the time is 5-60 seconds.

2. The method for preparing the silk protein erasable optical platform according to claim 1, characterized in that: In step S1, the degumming treatment method is: dissolving anhydrous sodium carbonate in boiling water to prepare a sodium carbonate solution with a concentration of 0.02M, then adding the silkworm cocoon fragments into the solution and boiling for 30 minutes to remove the sericin, then scrubbing with deionized water for 3-5 times, and drying to obtain degummed silk.

3. The method for preparing the silk protein erasable optical platform according to claim 1, characterized in that: In step S1, the hydrophobic treatment method is: after cleaning the silicon substrate, put it into a vacuum drying oven, add 100 μL of trichloro(1H,1H,2H,2H-perfluorooctyl)silane, and let it stand for 20 minutes under a vacuum environment.

4. The method for preparing the silk protein erasable optical platform according to claim 1, characterized in that: In step S1, the thickness of the silk protein film is 30-200 μm.

5. The method for preparing the silk protein erasable optical platform according to claim 1, characterized in that: In step S2, the material of the elastomer substrate is polydimethylsiloxane, and the thickness is 0.5-2 mm.

6. The method for preparing the silk protein erasable optical platform according to claim 1, characterized in that: In step S3, the pressure is 0.16-0.32 MPa.

7. The method for preparing the silk protein erasable optical platform according to any one of claims 1 to 6, characterized in that: In step S3, the diffractive optical element template is a blazed grating, a holographic grating, a microlens, a two-dimensional photonic crystal, or an optical diffraction element with a stepped micro-nanostructured surface.

8. The method for preparing the silk protein erasable optical platform according to any one of claims 1 to 7, characterized in that: The step S3 is replaced by the following method: attaching an elastomeric mask with a hollow pattern on one side of the silk protein film of the silk protein film-elastomeric substrate complex, and then placing it in water vapor for fumigation, taking it out after the end, removing the elastomeric mask, placing the diffractive optical element template on the silk protein film of the silk protein film-elastomeric substrate complex, applying pressure for imprinting, and after the silk protein film returns to the ambient humidity, peeling off the diffractive optical element template and the elastomeric substrate to obtain a silk protein erasable optical platform.

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