Super-resolution imaging of multiple cells by optimized flat-field epi-illumination

Biological processes are inherently multi-scale, and supramolecular complexes at the nanoscale determine changes at the cellular scale and beyond. Single-molecule localizationmicroscopy (SMLM)(1-3) techniques have been established as important tools for studying cellular features with resolutions of the order of around 10 nm. However, in their current form these modalities are limited by a highly constrained field of view (FOV) and field-dependent image resolution. Here, we develop a low-cost microlens array (MLA)-based epi-illumination system-flat illumination for field-independent imaging (FIFI)-that can efficiently and homogeneously perform simultaneous imaging of multiple cells with nanoscale resolution. The optical principle of FIFI, which is an extension of the Kohler integrator, is further elucidated and modelled with a new, free simulation package. We demonstrate FIFI's capabilities by imaging multiple COS-7 and bacteria cells in 100 x 100 mu m(2) SMLM images-more than quadrupling the size of a typical FOV and producing near-gigapixel-sized images of uniformly high quality.