Solid immersion microscopy images cells under cryogenic conditions with 12 nm resolution

Super-resolution fluorescence microscopy plays a crucial role in our understanding of cell structure and function by reporting cellular ultrastructure with 20–30 nm resolution. However, this resolution is insufficient to image macro-molecular machinery at work. A path to improve resolution is to image under cryogenic conditions. This substantially increases the brightness of most fluorophores and preserves native ultrastructure much better than chemical fixation. Cryogenic conditions are, however, underutilised because of the lack of compatible high numerical aperture objectives. Here, using a low-cost super-hemispherical solid immersion lens ( super SIL) and a basic set-up we achieve 12 nm resolution under cryogenic conditions, to our knowledge the best yet attained in cells using simple set-ups and/or commercial systems. By also allowing multicolour imaging, and by paving the way to total-internal-reflection fluorescence imaging of mammalian cells under cryogenic conditions, s uper SIL microscopy opens a straightforward route to achieve unmatched resolution on bacterial and mammalian cell samples. Lin Wang et al. present a new super-resolution modality using a super-hemispherical immersion lens. They achieve a 12 nm spatial resolution in cells under cryogenic conditions, which offers the technical means to study bacterial and mammalian cell samples at molecule localisation length-scales.