Hybrid method boosts microscopy resolution

Two methods are better than one, at least when it comes to improving resolution in microscopy. Stimulated emission depletion (STED) microscopy uses a doughnut-shaped laser beam to precisely control the location of fluorophore activation on a labeled sample. STED typically has resolution that is 10-fold better than diffraction-limited microscopy. In expansion microscopy, a fixed sample is embedded in a hydrogel, which swells and stretches the sample to four times its original size, leading to a physically generated improvement in resolution. Now, Alf Honigmann of the Max Planck Institute of Molecular Cell Biology & Genetics, Helge Ewers of Free University of Berlin, and coworkers report that ExSTED—the combination of the two methods—has 30-fold better resolution than diffraction-limited microscopy (ACS Nano 2018, DOI: 10.1021/acsnano.8b00776). The researchers used the hybrid method to image the microtubule network of cells in three dimensions. Because expanding the sample spreads out the fluorescent labels, the signal from any given area is greatly reduced. To counteract the signal reduction, the researchers used multiple antibodies to increase the number of fluorescent labels added to the microtubules. They hope to further improve the resolution by expanding samples a second time and finding ways of amplifying the fluorescence signal.