Invited: Expansion Microscopy, Opportunities and Challenges

Super-resolution fluorescence microscopy technology is revolutionizing multiple areas of biology by enabling the observation of how bio-molecules are organized at the nano-scale, and thus unravel how biological machinery operates. Nevertheless, imaging large volumes with localization-based super-resolution microscopy technology is currently impractical and imaging deep inside scattering tissue is infeasible. In this talk, I will explain how an alternative approach utilizing physical, isotropic magnification of tissue samples embedded in hydrogels, Expansion Microscopy (ExM), overcomes these limitations and allows nano-scale imaging of large biological samples. First, I’ll present the basic ExM protocol, allowing to reach a resolution of 60-70 nm using standard optical-sectioning fluorescence microscopes, by 4-fold expansion of fixed tissues. Then, I’ll show several examples of how ExM can be applied to generate transformative data in the areas of neuroscience – capturing cellular and synaptic morphology, and in developmental biology – capturing the fine structure of intra-nuclear channels suggested to have a role in gene expression regulation. Finally, I’ll present the typical properties of ExM image data, its advantages and limitations, and explain how recently and currently developed variants of ExM address these limitations and expand the realm of nano-scale imaging possibilities even further.