Transmission Microsphere‐Assisted Dark‐Field Microscopy

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‐µm‐diameter glass microsphere combined with an optical microscope, opening new possibilities for biological imaging.