Preparation And Optical Properties Of Silk Fibroin Micro-hemispheric Resonator

As a natural biological protein and polymer material,silk is not only used in the field of ordinary clothing,but also widely used in food,medicine and materials application prospects for its great mechanical properties,biodegradability and biocompatibility.As an important part of the laser,the resonant cavity plays an important role in light enhancement and screening.The preparation of the resonant cavity is also increasingly concerned by researchers.At present,the materials of the resonant cavity are mostly concentrated in inorganic materials,and have the large size,which limits its application in the field of biomedicine.The silk protein is made into a microcavity structure and given the performance as an optical resonant cavity,so that applicated to a micro laser.Not only can the special biocompatibility of silk be used to apply micro lasers to the field of biomedical testing,to reduce environmental and human hazards,at the same time,can also expand the application of silk in optical materials.Based on the previous research of silk micro-hemispheres preparation,in this research,the silk protein micro-hemisphere cavity with regular array and good shapes were prepared.By in-depth discussion of the influencing factors of micro-hemisphere preparation and optimization of experimental conditions,its optical performance was tested,and the possibility as a resonant cavity was initially discussed,which laid a foundation for the application of silk protein micro-hemispheres in micro lasers.This paper carried out preliminary research in the following aspects:1.Film preparation: The method of spin coating layer by layer self-assembly was used to prepare the polystyrene and silk protein double-layer membrane.The polystyrene film thickness ‘y' has a logarithmic relationship with the acceleration ‘x',y =-45.23ln(x)+ 456.01(R2 = 0.9947).By changing the spin coating acceleration,polystyrene films of different thicknesses can be prepared.Using an acceleration of 2500 rpm / s,a polystyrene film with a thickness of 100 to 110 nm could be obtained with a uniform distribution.The film formation time of silk membranes was greatly influenced by the environmental humidity.The higher the humidity,the longer the film formation time.When the humidity was less than 60 %,the film formation took only 2 minutes;2.Optimization of photolithography process: By exploring the influence of the photolithography process(hydrophobic treatment of silk protein film surface,type of photoresist,and development time)on the array pattern,it was found that the main factor that causes the photoresist pattern on the surface of the silk protein film to fall off is the development time.Shortening the development time(15 ? 20 s)could ensure the photoresist forms an array pattern on the surface of the silk protein film and maintains a good arrangement;3.Optimization of micro hemisphere preparation process: By analyzing the influence of the characteristics of the substrate material,the thickness of the silk film,the pattern morphology and the type of solvent on the number and morphology of the micro hemispheres,it was found that a silicon or silicon dioxide substrate was used and subjected to HMDS hydrophobic treatment,the thickness of silk was 80 ? 100 nm,the pattern morphology was 50 × 50 ?m,and acetone was used as a solvent to form a single micro hemisphere with good roundness(Roundness = 0.92 ± 0.05)on the array pattern;4.Optical performance testing of micro-hemisphere: Using confocal microscopic Raman spectroscopy to detect the photoluminescence properties of micro hemispheres,it was found that the 458 nm solid-state laser has minimal damage to the silk protein itself,and can excite the silk protein to produce a fluorescent signal in the wavelength range of 500 ? 600 nm,but the signal was weak.Comparing the photoluminescence characteristics of the silk protein membrane 2D pattern and the 3D micro hemisphere,it was found that the 2D pattern almost had no limiting effect on the fluorescent signal,while the 3D micro hemisphere had a limiting effect on the fluorescent signal,but it was weak,that is,the quality factor of the microcavity is low(Q = 179).5.Gain material of perylene: Using the perylene,a kind of fluorescent dye,as the gain material to modify the surface of the silica microspheres wrapped with silk protein,it was found that under the excitation of a 400 nm solid laser,perylene can effectively enhance the quality factor of the microsphere cavity,thus adding perylene to 3D micro hemisphere cavity lays the foundation to improve its quality factor.6.The next research plan: The research speculates that the roundness of the micro hemisphere < 1,the low surface smoothness of the silk membrane,and the weak autofluorescence signal of the silk protein might be the three main factors that restrict the low quality factor of the micro hemisphere cavity.It can be studied from three aspects: enhancing the hydrophobicity of the substrate,improving the smoothness of the surface of the protein film,and adding gain medium perylene to improve the quality factor of the micro-hemispherical resonator.