Observe living cells by use of a new DNA stain

Though bio-imaging is helpful to visualize the inner workings of a cell while it is still alive, the living cells put under the microscope risk being killed by the light and the fluorescent dyes used to highlight their structures. It is much like sunburnt - live cells are sensitive to intense light and the ultraviolet and blue lights used in live-cell imaging are the most dangerous. Now, EPFL scientists have developed a new DNA stain that can be used to safely image live mammalian cells for days even under demanding imaging conditions.
The work about this new DNA stain is published in Nature Communications.
Fluorescent stains that light up a cell's DNA allow people to track key biological processes such as cell division thus they are popular in live-cell imaging. But current DNA stains are themselves toxic or require types of light that can damage the cells. Ideally, a safe DNA fluorescent stain would be activated in the safer far-red spectrum of light.
What's more, a lot of DNA stains are not compatible with super-resolution microscopy, a modern imaging technique that can capture images of cells at higher resolution than that allowed by regular microscopes. So the bio-imaging community has been waiting for a DNA stain that shows low toxicity, works with far-red light and can be used in superresolution microscopy.
The lab of Kai Johnsson at EPFL has now developed a DNA stain that can satisfy all of the needs. The scientists combined two molecules together - One is a fluorescent molecule (silicon rhodamine or SiR) that works in the far-red spectrum and was previously developed in Johnsson's lab, and the other one is a well-known DNA stain Hoechst (the chemical name is bisbenzimide). Finally, the scientists named the DNA stain "SiR-Hoechst".
The new stain works by binding to a part of the DNA helix known as the "minor groove". Once bound, it turns on and emits a bright fluorescent red light. This is a tremendous advantage, as the stain produces very little noise - if it has not found its target, it stays "off". More importantly, SiR-Hoechst can bind to DNA without affecting its biological function in the cell. And because all cells possess DNA, the probe can be used across numerous species, types of cells, and tissues.
There is little risk of damage to cells because SiR-Hoechst works with far-red light. Besides, the light that it emits can be easily distinguished from any background fluorescence of living cells. These features give SiR-Hoechst a clear advantage over other DNA stains - it can safely maintain high-quality staining in live cells for over 24 hours, allowing biologists to identify individual cells in tissue or culture, or track delicate processes in real time.
This stain can be used in live-cell super-resolution imaging, helping to solve problems in DNA imaging in cells and biological tissues with exquisite resolution.
The SiR-Hoechst makes bioimaging safer. That is, it realizes the dream of observing details of nature without impacting them.
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