Microsphere-assisted microscopy allows the limit of the diffraction of light to overcome while being non-invasive, full-field, label-free, and easy-to-implement. However, the observation of translucent samples remains difficult using a classical bright-field illumination. In this work, a method is presented for the inspection of quasi-transparent sub-diffraction-limited structures by using dark-field illumination in the transmission mode. Glass-imprint features, having a size of 250 nm, as well as fixed mouse brain cells have been visualized using the dark-field microsphere-assisted technique. The possibility to observe feature sizes up to 100 nm has been demonstrated in air using a 25-mu m-diameter glass microsphere combined with an optical microscope, opening new possibilities for biological imaging.
Physica Status Solidi-Rapid Research Letters, vol. 13 (2), p. 4, Feb 2019.