Safer lasers to map your cells could soon be in the offing – all thanks to the humble jellyfish.
A combined team of researchers from Scotland and Germany has developed a way to create a polariton laser by using jellyfish proteins cultivated in E. coli cells. In their paper published in the journal Science Advances, the team describes their technique and possible uses for the result.
Conventional lasers, like the pointer you might use to entertain your cat, produce light by emitting identical photons after they have bounced around inside a cavity. But scaling these up requires lots of energy.
Another type of laser – called a polariton laser – works by passing photons back and forth between excited molecules. Unlike in conventional lasers, the photons are released and reabsorbed within the device itself before zooming out as laser light. These can use less energy than conventional lasers, so in theory could lead to more efficient optical communications or medical lasers that are less destructive to living tissue.
But there’s a problem: most polariton lasers only work well at extremely low temperatures. Switching the light-producing molecules to ones that operate at room temperature could make them more practical, says Malte Gather at the University of St. Andrews, UK. But the few materials that work at room temperature have light-emitting molecules that sit too close together, interfering with one another instead of producing laser light.
So Gather turned to an unusual solution: barrel-shaped fluorescent proteins engineered from jellyfish DNA. Each protein’s cylindrical shell encloses a component that emits light, and keeps those molecules from getting too cozy and interfering with one another.
To make the new laser, the researchers grew enhanced green fluorescent protein from jellyfish in E. coli cells because prior research suggested they were capable of producing polaritons (quasiparticles that are able to carry excitations with them). The protein was fashioned into a very thin (500 nanometer) film that was set between two mirrors. To create a laser beam, all the researchers had to do was shine a blue light into the device, which excited the proteins to the point of producing polaritons—soon thereafter, they spontaneously synchronized, producing a laser beam that was emitted out of the device.
“To me it looked like something that could be useful,” says Gather. Previously, his team had built a more conventional laser out of green fluorescent protein, but had never built a protein-based polariton laser.
To build their laser, Gather and his colleagues sandwiched a thin film of the fluorescent protein between two mirrors. Activating the light-emitting molecules with a pulse of blue light from an external laser successfully coaxed laser light from the proteins.
The laser might someday go back to its biological roots – it could be embedded within cells and used like a beacon to mark and track them by doctors or researchers.
Fluorescent proteins can already be embedded inside living tissue for this reason, but they emit such a broad range of wavelengths that they can differentiate fewer than 10 cell types. Because a laser emits such a narrow spectrum of light, fluorescent protein lasers could be used to mark thousands of different cells. And a fluorescent protein laser would be safer than embedding lasers with conventional semiconductors, which can be poisonous.
“You label each cell with a different laser, and then you just collect this light,” says Gather. “You can look at the wavelengths of the light and say, ‘Aha, this is this cell, because the laser light it emits has this particular wavelength’.”
The low energy requirements of the laser would be beneficial, too, he says. “If you work in living tissue, you don’t want to strain the tissue or the cells with too much energy.”
Admittedly, there are a few more challenges to overcome before the jellyfish-based laser is ready for everyday use, says Stéphane Kéna-Cohen at École Polytechnique de Montréal in Canada. “This is just cool from a fundamental standpoint,” he says.
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