Single-molecule localization microscopy-near-molecular spatial resolution in light microscopy with photoswitchable fluorophores.

Fluorescence imaging beyond the diffraction limit has grown into a method of choice to elucidate questions related to biological structure and organisation. Among super-resolution techniques, imaging based on the localization of individual photoswitchable fluorescent probes has become particularly popular due to its relative ease of implementation and the nature of qualitative and quantitative answers it can offer. We review the field of single-molecule localization microscopy (SMLM) by providing an overview of its underlying principles and of different categories of photoswitchable fluorophores. In addition to summarizing target-specific labelling strategies and presenting examples of successful applications of SMLM in fixed and living systems, we show how SMLM data offer unique opportunities for quantitative biomolecular counting and distribution analysis.