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In order to track individual cells in live-cell imaging, fluorescent DNA stains can be used as intracellular reference markers. Hoechst 33342 would be the best option to monitor cell proliferation in live-cell imaging since it is highly selective for DNA, fluorogenic in wash-free imaging and applicable in different cell types. However, Hoechst 33342 shows toxicity to live cells in long-term exposure because of the phototoxic effect of blue light required for its excitation.
Researchers from the Ecole Polytechnique Fédérale in Lausanne, Switzerland, recently published in "Nature Communications" the synthesis of SiR-Hoechst by the attachment of carboxylated silicon-rhodamine derivatives to the DNA-targeting bisbenzimide core of Hoechst, which permit the generation of a far-red probe. The far-red excitation and emission minimize phototoxic effects and the Hoechst core grants a high nuclear-staining specificity. The authors report that SiR-Hoechst shows a bright and highly specific nuclear stain in live cells and it does not impair cell proliferation after 288 far-red emissions within a 24 hours measurement interval. Therefore, SiR-Hoechst is likely to be a new powerful tool for long-term live-cell imaging and for kinetic studies of cell proliferation.
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Images of fibroblasts and HeLa cells treated with SiR-Hoechst.
This image belongs to figure 2 of the original paper in Nature Communications.