Comparison between microsphere-assisted and confocal microscopies

We show that microsphere-assisted microscopy, where liquid-immersed barium titanate glass (n ~ 1.9) beads with diameters of several microns are employed, has superior optical resolution compared to the confocal microscopy. The resolution advantage of microsphere-assisted microscopy stems from an ability of high-index microspheres to pick spatial distribution of optical near-fields produced by the plasmonic nanostructure used in our experiments. It is shown that an additional advantage of imaging through liquid-immersed microspheres is the ability to achieve high resolution imaging using microscope objectives with moderate numerical apertures. This means that microsphere-assisted microscopy can be performed with longer working distances compared to conventional or confocal microscopy. Super-resolution microscopy by using liquid-immersed microspheres can be potentially used in biomedical microscopy, microfluidics, and nanophotonics applications.