To reveal the intricacies of how cells function, many assays work. However, nothing can compare to watching those process live in the cell. Then, numerous dyes and labels have been designed for live-cell imaging. But, even with this numerous choices, such studies are often complicated by toxic by toxic dyes, difficult labeling protocols, dye specificities and above all, phototoxicity following extended light exposure. In a recent study published in the journal Nature Communications, researchers have described that they have designed a new DNA specific fluorescent dye, SiR-Hoescht, which can overcome those problems.

“The introduction of SiR-Hoechst makes bioimaging closer to its main goals, namely, to observe the wonders of nature without disturbing them.” Commented Kai Johnsson of Ecole Polytechnique Federale de Lausanne, senior author of the new article.

In general, researchers label DNA with fluorescent dyes to monitor individual cell nuclei or follow processes like mitosis. Hoescht, however, is quite suitable for these applications, because it’s toxic-free to cells in the concentrations needed for labeling nuclei. Although cells tolerate the Hoescht dye well, they do not respond as well to the blue light illumination needed to visualize it and often suffer considerable phototoxic damage that hampers longer image studies. On the other hand, another commonly used DNA dye, DRAQ5 can be imaged using far-red light that causes little cell damage. But since the dye itself is toxic, it can not be used for the application in live-cell microscopy.

In previous experiment, Johnson’s group showed that when attached carboxylated silicon-rhodomaine (SiR) derivatives to targeting ligands, they created far-red probes for live-cell imaging. Upon this success, they decided to modify Hoescht in the same way, making ti possible for DNA labeling in live cells as well as avoid phototoxicity.

“Featured as: favorable spectroscopic properties, good biocompatibility, and applicability to STED microscopy, SiR-Hoescht is a powerful tool for the imaging of DNA in living cells or tissues.” wrote the authors.