Credit: Public Domain.

In something that seems out of a Philip K. Dick novel, researchers injected a nanoparticle solution into the eyes of mice, granting them the ability to see in infrared. Normally, the eyes of rodents, or humans for that matter, cannot perceive infrared electromagnetic radiation, although they can sense it in the form of heat.

Super vision

Most mammals, including people, can only see in a narrow range of the electromagnetic spectrum, called visible light. The visible spectrum extends from 380 nanometers to 740 nanometers, which is outside the infrared spectrum whose wavelengths extend from 800 nanometers all the way one millimeter.

“When light enters the eye and hits the retina, the rods and cones–or photoreceptor cells–absorb the photons with visible light wavelengths and send corresponding electric signals to the brain,” Gang Han at the University of Massachusetts Medical School, said in a statement. “Because infrared wavelengths are too long to be absorbed by photoreceptors, we are not able to perceive them.”

Infrared or thermal cameras are equipped with detectors that can translate infrared radiation by assigning each temperature a shade of a color. Colder temperatures are often given a shade of blue, purple, or green, while warmer temperatures can be assigned a shade of red, orange, or yellow.

We don’t know how exactly the mice in this experiment perceived infrared through their vision, but what seems likely is that they could.

Researchers at the University of Science and Technology in China and the University of Massachusetts Medical School developed nanoparticles that bind to the eye’s existing structures. Once the nanoparticles anchor to photoreceptor cells, they act as tiny infrared light transducers. When infrared light hits the retina, the longer infrared wavelengths are re-emitted into shorter wavelengths within the visible light range. So, technically, the mice don’t really see infrared — they see infrared information in a perceptible form, which is exactly how a thermal vision camera works.

“In our experiment, nanoparticles absorbed infrared light around 980 nm in wavelength and converted it into light peaked at 535 nm, which made the infrared light appear as the color green,” said Jin Bao at the University of Science and Technology of China.

Nanoparticles (white) bind to rods and cones in the retina of mice, allowing the rodents to sense infrared. Credit: Current Biology.

Mice injected with the nanoparticles showed various signs that they were able to detect infrared, such as their pupils constricting. In an experiment, the mice were able to navigate a series of maze tasks — which their normal-vision peers could not — showing that they could simultaneously sense both infrared and visible light.

A single injection of nanoparticles in the mice’s eyes bestowed infrared vision for up to 10 weeks. Although there was a minor side effect (a cloudy cornea), it disappeared within less than a week. Tests found no damage to the retina’s structure, suggesting that the procedure is safe.

Illustration of the infrared-to-visible-light conversion process. Credit: Cell.

“In our study, we have shown that both rods and cones bind these nanoparticles and were activated by the near infrared light,” says Xue. “So we believe this technology will also work in human eyes, not only for generating super vision but also for therapeutic solutions in human red color vision deficits.”

“In the future, we think there may be room to improve the technology with a new version of organic-based nanoparticles, made of FDA-approved compounds, that appear to result in even brighter infrared vision,” says Han.

In the future, the researchers plan to tweak their nanoparticles to better suit human eyes, which have more cones and rods than mice.

“This is an exciting subject because the technology we made possible here could eventually enable human beings to see beyond our natural capabilities,” says Xue.

The findings appeared in the journal Cell.