Light fantastic (Image: Matjaž Humar and Seok Hyun Yun)

Individual cells have been turned into tiny lasers. “It’s actually super-easy,” says Matjaž Humar of Harvard Medical School. The feat allows cells to be labelled and monitored more accurately, which could boost our ability to track the spread of diseases such as cancer.

Humar and his colleagues developed three ways to get cells to emit visible light. The first involved injecting each one with a tiny oil droplet, forming an optical cavity which could be filled with fluorescent dye. Shining a light pulse on to the cavity excited the dye atoms into emitting light in a tightly focused beam.


They also scattered polystyrene beads 10 micrometres wide into a Petri dish filled with macrophages, a type of white blood cell that ingests foreign material. Once these cells had ingested the beads, they performed the same function as the oil droplets, emitting laser light when excited.

The final way involved exploiting the fatty droplets that exist naturally within living cells. “We all have these fat cells inside our tissue. We are all made of lasers,” says Humar. The first two approaches were tested on human cells, the last on pig cells.

A shining achievement (Image: Matjaž Humar and Seok Hyun Yun)

Tagging cells with fluorescent dyes is a common and relatively easy way for researchers to label cells by getting them to emit light, but this produces a relatively broad range of wavelengths, making it difficult to distinguish between differently tagged cells.

However laser light is characterised by having an extremely narrow range of wavelengths. That means it is theoretically possible, using these new techniques, to give every single cell in the human body a unique, identifiable laser signature, Humar says.

Humar’s results echo research published last week by Malte Gather and his group at the University of St Andrews, UK. Gather’s work, which focuses exclusively on the macrophage route to converting cells into lasers, goes further in laying out its potential applications.

Gather believes it will be useful primarily for monitoring how tumour cells spread, as well as how individual immune cells respond to inflammation and migrate to the affected sites. We could also use this technique to study the early development of complex organisms, he says: “You could see where the cells migrate to and how the body acquires its shape.”

Journal reference: Nature Photonics, DOI: 10.1038/nphoton.2015.129 and Nano Letters, DOI: 10.1021/acs.nanolett.5b02491