New Technique Enhances Superresolution Microscopy

Researchers at Bielefeld University have demonstrated improvements in superresolution structured illumination microscopy (SR-SIM), demonstrating that the technique is possible in real time and at a very high imaging rate, which is enhancing observation of even the smallest cell particles.

“Unlike other conventional fluorescence microscopy methods, SR-SIM does not illuminate the specimens uniformly, but with a fine, grid-like pattern. This special technology enables much higher resolution,” said Thomas Huser, a physics professor and head of the Biomolecular Physics Working Group at Bielefeld. “The problem so far has been that microscopes offering a sufficiently high resolution cannot display information at the corresponding speed.”

This image taken by the new microscope shows a living bone cancer cell with nucleus (blue), mitochondria (green), and cytoskeleton (magenta). Courtesy of Bielefeld University/W. Hübner.

Traditionally, such microscopes have been slower than conventional ones, as more or finer image data had to be recorded, which took more time. According to the researchers, SR-SIM, a fluorescence microscopy procedure, irradiates objects with laser light. The light re-emitted by the specimen is recorded in several individual images, with the finished image then reconstructed on a computer from the raw data.

“The second step, in particular, has cost a great deal of time so far,” said study lead author Andreas Markwirth, a physics professor at Bielefeld and a member of the school’s Biomolecular Physics Working Group.

The researchers — with assistance from Rainer Heintzmann, a professor at Friedrich Schiller University and head of the microscopy research group at Leibniz Institute for Photonic Technologies — tested their technique on biological cells and recorded the movements of mitochondria. They were able to produce approximately 60 frames per second, which Markwith noted is a higher frame rate than cinema films. “The time between measurement and image is less than 250 milliseconds, so the technology allows real-time recording,” he said.

In their study, the researchers were able to use parallel computer processing on modern graphics cards to speed up image reconstruction. Now, the SR-SIM microscope can generate raw data faster.

Until now, microscopy techniques involved a conventional microscope finding the structures, while a superresolution microscope examined them in further detail.

“However, some structures are so small that they cannot be found with conventional microscopes, for example specific pores in liver cells,” Huser said. “Our method is both high resolution and fast, which enables biologists to explore such structures."

SR-SIM can be especially effective in medicine and biology applications. It could also be used in the study of viral particles as they pass through a cell, which the researchers said can allow a better understanding of exactly what happens during infection processes.

The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-12165-x).