The finding could make for significant improvements in cell imaging, used frequently in research on cancer and infectious diseases.

It’s already common for researchers to tag cells with dye. In current imaging techniques, dyed cells emit a broad range of wavelengths, making it difficult to distinguish one cell from another. Lasers work in a much narrower range, making it theoretically possible for researchers to give each cell an individual laser light signature.

“Maybe the most interesting application is cell tagging, so you can see how the cells move,” Humar told Quartz.

So far they’ve only tagged cells in Petri dishes, but Humar says there’s no reason it wouldn’t work in a living body. “In principle, it could be possible to individually tag and track every single cell in the human body,” he and Yun wrote in a blog post for Discover.

One day, they say, intracellular lasers could even help determine what a cancer cell is made of, by allowing doctors to analyze the interior with the laser light instead of a biopsy.

The Harvard team isn’t alone in its research on turning cells into lasers. As New Scientist reported, a group at the University of St. Andrews in the UK has also worked with using macrophages to create intracellular lasers.

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