Nanoparticles give mice night vision | Science


Mice injected with specialized nanoparticles can see infrared light showing various patterns and shapes to help them navigate an aquatic labyrinth.

Yuqian Ma, Wenyang Yi, Jiawei Shen

By Robert F. Service

Scientists have discovered how to confer a superpower, similar to that of the mythical X-Men, at least to the mouse. Using nanoparticles that convert infrared (IR) light into visible light, researchers gave mice the ability to see in the dark. If the same technique works in humans, it could offer soldiers a night vision without the need for goggles and possibly against the ills that cause patients to gradually lose their eyesight.

"This document is breathtaking," says Michael Do, a neuroscientist at Harvard Medical School in Boston, who did not participate in the work. "To think that you can inject these nanoparticles and make them work is incredible."

When injected into the eye, the nanoparticles diffuse visible light to the light-sensitive pigments that vertebrates use to see. The pigments are in specialized cells called photoreceptors, located in the retina at the back of the eye. A combination of pigments in these photoreceptors absorbs different light colors, which causes the transmission of nerve impulses through the optic nerve to the visual centers of the brain. Humans have three pigments that give us a color vision and another pigment that helps us see black and white, especially in low light. Mice and some primates have only two color pigments and one for dim light.

Researchers have previously added genes for a third pigment to mice and primates to give them a similar sensitivity to that of humans in visible light. But until now, no mammal has been able to see infrared light under normal conditions.

To change this, Xue Tian, ​​an expert in vision physiology from the University of Science and Technology of China in Hefei, has teamed up with Gang Han, an expert in nanoparticles from the faculty of medicine from the University of Massachusetts to Worcester. Han had previously developed nanoparticles capable of converting infrared to blue light. Since blue light carries more energy than the infrared, these uplink nanoparticles (UCNP) must absorb several infrared photons before releasing a single blue photon. This has led Han and Xue to wonder if such nanoparticles on photoreceptors would convert enough IR into visible light to allow mice to see in the dark.

Mice injected with specialized nanoparticles can see infrared light showing various patterns and shapes to help them navigate an aquatic labyrinth.

Yuqian Ma, Wenyang Yi, Jiawei Shen

To find out, Han and his colleagues first improved the chances of the animals: they modified the UCNP to give a green light. (Green photopigments in animals are more sensitive than blue.) They then coated their UCNPs with a protein that binds to specific sugar molecules located on the photoreceptor membranes. After injecting these substances behind the mouse retina, they discovered that UCNPs were tightly bound to photoreceptors and remained there for up to 10 weeks without any obvious long-lasting side effects.

And the nanoparticle injections seemed to have the desired effect. The mice that received them showed physical signs of infrared light detection and conversion to visible light: their pupils were contracted, for example, while the mice injected with a buffer solution did not react. Electrophysiological recordings have also shown that the nerve responses triggered by IR light in the retina and visual cortex were restricted to animals carrying nanoparticles.

Finally, Xue, Han and their colleagues subjected the mice to behavioral tests to determine whether animals containing nanoparticles saw a diffuse haze or were able to recognize distinct shapes and patterns. During a test, the animals swam in a water maze without a way out. On the wall above a route, the researchers projected a triangle and on another, a circle; below the triangle, the researchers placed a submerged platform on which animals could climb to get out of the water.

When the forms were illuminated with visible light, all the animals quickly learned to associate the triangle with the comfort of the platform and to swim immediately towards it, even when the researchers exchanged the position of the triangle and the circle. When the patrons were under IR light, only the animals injected with the UCNP were constantly swimming towards the triangle, the researchers said today. Cell. "The students could not see which one [pathway] showed the triangle, but the mice were on the right side, "Xue said with a chuckle.

Given the similarities between the mouse and man in the physiology of vision, Xue said, "I really think it will work in humans." In this case, future versions of nanoparticles could give first responders and military personnel improved night vision on a temporary basis. The nanoparticles could also be designed to absorb and re-emit visible light. These particles may intensify the color sensation to treat patients with macular degeneration, a leading cause of age-related vision loss, in which photoreceptor cells gradually die over time.

The creation of other X-Men powers, such as telekinesis or time manipulation, will take longer.

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