Label-Free Super-Resolution Imaging of Transparent Dielectric Objects Assembled on a Silver Film by a Microsphere-Assisted Microscope

In optical microscopy, label-free imaging of transparent dielectric objects with subwavelength features is still a challenge. We propose a method to super-resolution image a label-free, transparent, periodic object using a microsphere-assisted bright-field microscope. A two-dimensional array of label-free, hexagonally close-packed polystyrene (PS) nanoparticles with a diameter of 250 nm assembled on a silver film-coated glass slide can be discerned by coupling a classical optical microscope to a 30 mu m-diameter BaTiO3 glass (BTG) microsphere. However, when the PS nanoparticle array with the same diameter is assembled on either a glass slide or a high-reflectance dielectric multilayer-coated glass slide, it cannot be resolved. We propose that period plasmonic near-field illumination is generated due to the excitation of surface plasmon polariton modes on periodically structured interfaces. More high-frequency information about the object is coupled with the BTG microsphere lens system, resulting in the improvement of imaging resolution.