Super-resolution microscopy is beyond the budgets of most labs – a challenge that prompted the invention of expansion microscopy (ExM) in 2015. ExM adheres tissue to an absorbent polymer that expands when wet, pulling biomolecules apart, such that a resolution of around 70 nanometers is achievable with a light microscope.
Credit: Courtesy of the researchers
Building on this work, a recent study published in Nature Methods introduces a new single-step method for ExM – known as 20ExM – which achieves 20-fold isotropic expansion in a single step. Led by Shiwei Wang and colleagues, the study addresses the complexity of previous methods that required multiple rounds of expansion to reach similar levels of magnification. The 20ExM protocol offers significant improvements in simplicity and resolution, achieving nanoscale imaging (<20 nm resolution) using conventional microscopes.
The core innovation lies in the development of a superabsorbent hydrogel that enables robust expansion while maintaining structural integrity of the molecular targets. By optimizing the polymer composition, specifically using N,N-dimethylacrylamide (DMAA) and sodium acrylate (SA), the researchers were able to achieve reliable expansion factors of 20x in a single step for both cell cultures and brain tissue.
To demonstrate the power of 20ExM, the researchers visualized nanoscale structures, such as the hollow microtubule architecture and synaptic nanocolumns in mouse brain tissue, with high fidelity. The technique was validated against iterative expansion microscopy (iExM) methods and showed comparable performance. For some tissues, such as kidney and spleen, the authors noted that additional optimization was required.
The researchers believe that 20ExM holds promise for use in various areas of biological research, including neuroscience, organelle imaging, and molecular biology.
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