A Study Of An Improved Method For Microsphere-assisted Microscopic Imaging

Diffraction limit makes the resolution of conventional optical microscopes to about?/2(?is the wavelength of the illuminating source).In order to explore the microscopic world below?/2,a variety of super-resolution imaging techniques had been proposed to break through the diffraction limit.Among these imaging techniques,a method that uses dielectric microspheres to assist optical microscopes had been shown to allow conventional optical microscopes to achieve resolution beyond diffraction limits under white light illumination.The study of the factors that affect the imaging performance of microspheres is helpful to find a way to improve the microsphere assisted imaging technology and make the microsphere assisted imaging technology more perfect.Therefore,it is of great significance to continue the research on the improved method to improve the performance of microsphere assisted microscopic imaging.In this paper,the method to improve the imaging performance of microspheres is explored by studying the refractive index of the sample,the surface characteristics of the sample and the substrate properties of the sample.The main contents of the study are as follows:1.The influence of sample refractive index on microsphere assisted microscopy was studied.This paper used Ba Ti O₃Glass(BTG)microspheres fully immersed in Polydimethylsiloxane(PDMS,n=1.4)assisted microscopic imaging technology to observe the hexagonal Polystyrene(PS,n=1.6)and Silica(SiO₂,n=1.46)nanoparticles with diameters of 250,300,and 400 nm.The experimental results show that the two kinds of samples with different refractive indices exhibit different experimental phenomena under the same imaging structure.It is shown that the relative refractive index between PDMS and the sample has an effect on the imaging when the sample surface is covered with submerged medium PDMS.When the relative refractive index between PDMS and the nanoparticle array is small,the scattering signal of the nanoparticle array is small and the contrast of imaging is poor,so the imaging system has a lower resolution when observing the SiO₂nanoparticle array.The results show that the refractive index of the sample can affect the resolution of the microsphere assisted imaging system.2.The method of improving the sample refractive index to affect the resolution of the microsphere assisted imaging system is studied.This paper used the BTG microsphere assisted imaging system to study the imaging of samples with different refractive indexes deposited with a 50 nm silver film on the surface.The experimental results show that under the BTG microsphere assisted imaging system,the PS and SiO₂nanoparticle arrays with diameters of 250 and 300 nm coated with 50 nm silver film can be distinguished.The reflectance spectra and intensity distributions of PS and SiO₂nanoparticle arrays coated with 50 nm silver films were simulated using the Finite Difference Time Domain(FDTD)method.The simulation results show that the surface plasmon polarition(SPP)wave with evanescent wave point can be excited on the surface of PS and SiO₂nanoparticle array at the minimum value of reflection spectrum.The near-field enhancement effect of SPP wave is conducive to the coupling of high-frequency information on the sample surface into the microsphere to improve the system resolution.The results demonstrate that evaporation of a silver film on the sample surface can counteract the influence of sample refractive index on the microsphere assisted imaging system,and the generation of SPP waves on the sample surface is helpful to improve the performance of the microsphere assisted imaging system.3.This paper studied the influence of the metal properties of the substrate where the sample was placed on the microsphere assisted imaging system.Prepared dispersed PS nanoparticles and hexagonal densely arranged PS nanoparticle arrays on 50 nm coated Au,Ag and Al substrates to explore the influence of different metal substrates on the microsphere assisted imaging system.The experimental results show that the BTG microsphere imaging system has good imaging performance when observing the dispersion and hexagonal densely arranged PS nanoparticles prepared on the aluminum film substrate.FDTD simulation results show that the unlabeled transparent medium with periodic structure is placed on the glass slide by thermal evaporation plating on a 50nm aluminum films.Due to the excitation of SPP,enhanced periodic plasma near-field illumination is generated,which improves the imaging resolution of the microsphere assisted optical microscope.