Microsphere-assisted Microscopy Imaging Studies Of Low-contrast Samples

The loss of high-frequency information on the sample surface is the main reason for the resolution limit of conventional optical microscopes.The evanescent wave carrying the fine structure information of the sample on the surface to be coupled into microsphere and then transformed into the propagating wave which can be captured by the objective lens,thus enabling the conventional optical microscope to have the ability of super-resolution imaging.Microsphere-assisted imaging technology does not require fluorescent labeling of samples,and the illumination light is not phototoxic.Superresolution imaging of low-contrast samples with sub-wavelength structures is always a difficult problem in the field of imaging.This dissertation studies the imaging characteristics of the microsphere-assisted super-resolution imaging technology when observing low-contrast objects with sub-wavelength structures,and studies the methods to improve the imaging performance of the microsphere-assisted imaging technology when observing low-contrast samples.The main research contents are as follows:1.The influence of deposition of 30-nm-thick Ag film on the surface of lowcontrast samples on the performance of microsphere-assisted imaging was studied.The low-contrast sample selected for the experiment is a single-layer hexagonally closepacked(hcp)polystyrene(PS)nanoparticle array with a diameter of 300 nm and 250 nm assembled on the surface of the glass slide.Using barium titanate glass(BTG)microspheres fully immersed in polydimethylsiloxane(PDMS)to assist the optical microscope to image the PS nanoparticle array with Ag coating on the surface.The results show that the microsphere-assisted imaging system can clearly resolve PS nanoparticle array samples with a diameter of 250 nm.The interface between the Ag film and the PS nanoparticle array can excite surface plasmon polariton waves with near-field enhancement characteristics.This near-field enhancement effect can improve the ability of the BTG microspheres to couple evanescent waves on the sample surface,thereby improving the imaging performance of the BTG microspheres on low-contrast samples.2.The influence of the substrate in microsphere-assisted imaging on its imaging performance was studied.The hcp PS nanoparticle arrays were prepared on a glass slide and a glass slide deposited with a 30-nm-thick Ag film.We use BTG microsphereassisted optical microscopy to perform imaging studies on low-contrast samples on different substrates.The experimental results show that the 300 nm diameter PS nanoparticle array prepared on the Ag film substrate can be clearly resolved,while the sample prepared on the glass slide cannot be resolved.The research results reveal that the substrate plays an important role in the imaging of low-contrast samples with microspheres.Subsequently,the imaging characteristics of the microspheres on nonperiodic low-contrast samples were studied.Finally,the PS nanoparticle array deposited with Ag film on the surface was used as the substrate,and the influence of the periodic structure substrate in the super-resolution imaging is studied.