Image source: Leibniz IPHT

By: Sven Dring

When trying to visualize finest details in cells, standard light microscopes reach their limits. As a doctoral student, Rainer Heintzmann discovered a method that can break this barrier. Today, he has improved the technique of super-resolution microscopy to such an extent that it is useful for applications in biology and medicine

In order to observe living cells at work, researchers have to overcome a physical law. One of the fastest techniques to overcome the resolution limit of classical light microscopy is high-resolution structured illumination microscopy.

It makes details in cells visible that are about one hundred nanometers in size, one hundred millionth of a millimeter. However, translating the recorded data back into images used to take a lot of time. Rainer Heintzmann, together with a team of researchers from Bielefeld University, has developed atechnique that allowsthe image data to be reconstructed directly.This allows researchers to watch biologicalprocesses in the cellvirtually live. "It enables completely newimaging workflows that no other high-resolution microscopy method currently allows in this way," says Rainer Heintzmann.

The graphics helps computer gamers to have a great gaming experience. Researchers use it to observe the smallest cell components in action - in real time and at a very high frame rate. "The image data can be reconstructed about twenty times faster than it would take on a PC," explains Rainer Heintzmann, who already laid the foundations for the structured illumination method in high-resolution microscopy as a doctoral student in 1998. In cooperation with the Bielefeld research team led by Thomas Huser, he further developed the technique of Super-Resolved Structured Illumination Microscopy (SR-SIM).

In the fluorescence microscopic SR-SIM method, objects are irradiated with laser light using a special pattern. It excites special fluorescent molecules in the sample so that they emit light at a different wavelength. The microscopic image then shows this emitted light. It is first recorded in several individual images and then reconstructed as a high-resolution image on a computer. "The second step in particular has taken a lot of time so far," says Andreas Markwirth from Bielefeld University, first author of the study, which the research team published in the renowned journal "Nature Communications".

For the new microscope, the research team used parallelcomputer processes on modern graphics and was thus able to significantly accelerate image reconstruction. A minimum delay of 250 milliseconds is hardly noticeable to the hu- man eye. The raw data can also be generated faster with the newly researched microscope.

Structures that are invisible to conventional microscopes

"This makes it possible to measure samples quickly and to immediately adjust test conditions during an experiment instead of having to evaluate them afterwards," says Rainer Heintzmann, describing the practical benefits of the new technology. It is only through the rapid reconstruction of images that "this type of microscopy becomes really useful for applications in biology or medicine," says Thomas Huser. "Because the problem so far is: microscopes that offer sufficiently high resolution cannot display information at the appropriate speed".

For their study, the scientists tested the method on biological cells and recorded the movements of mitochondria, the energy centers of the cells that are about one micrometre in size. "We were able to generate about 60 frames per second that's a higher frame rate than in motion pictures. There are less than 250 milliseconds between measurement and image, so the technology allows real-time recordings," says Andreas Markwirth.

Until now, super-resolution methods have often been combined with conventional methods: A conventional fast microscope is used to find structures first. These structures can then be examined in detail with a super-resolution micro- scope. "However, some structures are so small that they cannot even be found with conventional microscopes, for example special pores in liver cells. Our method provides both high resolution and speed this enables biologists to investigate such structures," said Thomas Huser. Another application for the new microscope is the investigation of virus particles on their way through the cell. "This enables us to understand exactly what happens during infection processes."

Publication: Andreas Markwirth, Rainer Heintzmann et al., Video-rate multi-color structured illumination microscopy with simultaneous real-time reconstruction, Nature Communications 10 (2019), https://doi.org/10.1038/s41467-019-12165-x

Source: Leibniz IPHT

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