High Res Microscopy at High Speed

Cutting-edge light microscopes offer resolutions of a few tenths of a nanometer, but until now, they have been much slower than conventional methods. But in a paper published today in Nature Communications, Bielefeld University researchers and their collaborators from Jena show that SR-SIM is also possible in real time and at a very high imaging rate—and is thus suitable for observing movements of very small cell particles, for example.

“This is what makes this type of microscopy really useful for applications in biology or medicine,” says co–corresponding author Thomas Huser. “The problem so far is that microscopes offering a sufficiently high resolution cannot display information at the corresponding speed.”

SR-SIM stands for “super-resolution structured illumination microscopy” and is a fluorescence microscopy procedure. Objects are irradiated with laser light. This light excites special fluorescent molecules in the sample so that they re-emit light at a different wavelength. The microscopic image then shows the re-emitted light.

“Unlike other conventional fluorescence microscopy methods, SR-SIM does not illuminate the specimens uniformly, but with a fine, grid-like pattern,” Huser says. “This special technology enables much higher resolution.”

For their study, the researchers tested the new method on biological cells and recorded the movements of mitochondria, which are about one micrometer in size. “We have been able to produce about 60 frames per second—a higher frame rate than cinema films,” says first author Andreas Markwirth. “The time between measurement and image is less than 250 milliseconds, so the technology allows real-time recording.”

Up to now, super-resolution methods have often been combined with conventional methods: A conventional fast microscope is used to first find structures, which are then examined in detail using a super-resolution microscope. “However, some structures are so small that they cannot be found with conventional microscopes—for example, specific pores in liver cells,” Huser says. “Our method is both high-resolution and fast, which enables biologists to explore such structures.”

Another application for the new microscope is the study of viral particles on their way through the cell, allowing researchers to better understand the infection process.