Incredible experience gives infrared vision to mice – and humans could be next


Special nanoparticles (in white) glued to rods (left) and cones (right) of mouse photoreceptors.
Image: Ma et al / Current biology

By injecting nanoparticles into the eyes of mice, scientists have allowed them to see light in the near infrared, a wavelength generally invisible to rodents (or humans). This is an extraordinary feat, made even more extraordinary by realizing that a similar technique could be used in humans.

Among all the remarkable things made to mice over the years, this latest achievement, described today in the scientific journal Cell, is one of the most science-fiction.

A research team, led by Tian Xue of the China University of Science and Technology and Gang Han of the University of Massachusetts Medical School, has modified the vision of the mice so that they can see near infrared light (NIR). to maintain their natural ability to see normal light. This was done by injecting special nanoparticles into their eyes, the effect lasted for about 10 weeks and resulted in no serious side effects.

A series of tests showed that the mice saw well infrared light and not other stimuli. Researchers say that the human eye is not so different from that of mice, which opens the fantastic path for the application of a similar technique to humans.

Humans and mice can only see a limited range in the electromagnetic spectrum, indicated here by the rainbow-shaped band. Other animals, including birds, can see ultraviolet (UV) rays.
Picture: Cell

Humans, like mice, have visual access to a limited range of the electromagnetic spectrum. The range of wavelengths invisible to humans is vast and we can not see anything outside the so-called visible spectrum (wavelengths between 380 and 740 nanometers). Infrared radiation exists in the form of longer wavelengths along the spectrum, ranging from about 800 nanometers to a full millimeter. Past infrared is the longer wavelengths of microwaves and radio waves

Objects in the world, be it people or a bowl of hot soup, or something as cold as an ice cube, emit infrared radiation as you go that they give off heat. Mammals like humans and mice can not see NIR, but we have technologies, such as night vision goggles or thermal vision, that can convert this otherwise invisible spectrum into a visible format. The new technique used on mice has something similar, but instead of relying on wearable technology, scientists have immersed themselves in the biology of the business.

In order to allow mice to see beyond the usual visual spectrum, Tian and Gang have developed special "conversion enhancement" nanoparticles that can function in pre-existing eye structures of rodents. Drops of liquid containing the minute particles were injected directly into the eyes, where, thanks to special anchors, they fixed themselves firmly to the photoreceptor cells. Photoreceptor cells – rods and cones – normally absorb the wavelengths of incoming visible light, which the brain interprets as a vision. In the experiment, however, the newly introduced nanoparticles converted the incoming NIR into a visible wavelength, which the mouse brain was then able to process as visual information (in this case , the NIR was considered a greenish light). The nanoparticles hung for nearly two months, allowing the mice to see both NIR and visible light with minimal side effects.

Graphical representation of the process in action. When the infrared light (red) reaches a photoreceptor cell (light green circle), the nanoparticles (pink circles) convert the light into visible green light.
Picture: Cell

Essentially, the nanoparticles on the photoreceptor cells served as a transducer or converter for infrared light. The nanoparticles captured in the retina the longest infrared wavelengths, which then relayed them as shorter wavelengths in the visible light range. The rods and cones, designed to absorb the shorter wavelengths, were thus able to accept this signal, and then send that converted information to the visual cortex for processing. Specifically, the injected particles absorbed the NIR around 980 nanometers wavelength and converted it to light in a 535 nanometer area. For mice, this meant seeing the infrared light in green. The result was similar to seeing NIR with night vision goggles, except that the mice were also able to maintain their normal vision of visible light. As noted, the effect was temporary and lasted a few weeks. Some mice had a cloudy cornea, which quickly cleared up.

To prove that the method really worked, Tian and Gang set up a series of tests and experiments.

For example, the pupils of the injected mice were dilated when exposed to NIR, unlike the pupils of mice without injection. And when exposed exclusively to NIR, measurements of brain electrical activity in injected mice showed that the eyes and visual cortex functioned as in the presence of visible light.

Behavioral tests also showed that the method worked. Mice placed in a Y-shaped water labyrinth learned to recognize the location of a hidden platform in which they sought refuge, which was indicated by a display illuminated by the PIR. In the tests, the injected mice systematically located the platform while the mice without injections were randomly swimming around the labyrinth. Another test consisted of a box with two compartments: one completely black without light and the other lit with NIR. Mice, nocturnal creatures, gravitate in the dark. In the tests, the injected mice spent more time in the dark compartment, whereas the uninjected mice showed no preference.

"These in-depth experiments leave no doubt that mice injected with infrared-sensitive nanoparticles gain the ability to detect infrared light and obtain visual information," said Vladimir J. Kefalov, professor of ophthalmology and vision science at the Washington University of St. Louis. was not affiliated with the new study, said to Gizmodo.

In a press release, Tian said that the nanoparticles attached to both the stems and cones and that they were activated by near infrared light. We are therefore convinced that this technology will also work in human eyes, not only to generate vision, but also for therapeutic solutions. visual impairment of red color in humans. In an interview with Cell, he said:

Unlike mice, humans and other primates have a structure called fovea in the retina, which provides high-acuity central vision. In the human fovea, the density of the cones is much higher than that of the rods; while in the retina of the mouse, the number of rods predominates everywhere … The cones having a spectrum and a sensitivity of different intensity to the light compared to the rods, we will perhaps need to adjust the UCNP's emission spectrum to more effectively activate a particular type of cones in humans.

As Tian noted, the treatment should be modified for humans to work, but the new experience suggests that it is possible. Kefalov said that the potential of applying a similar concept in humans was both real and exciting, but warned that the road ahead is still long.

"The authors demonstrate that a single injection of nanoparticles has no long-term detrimental effect on the mouse retina," Kefalov said. "However, it is not clear if practical infrared vision in humans will require repetitive injections and, if so, whether such chronic treatment will have long-term adverse effects on the structure." and the function of our eyes. "

Acquiring the ability to see infrared light looks like science fiction and transhumanistic fantasies (the raised hand), but it would be an undeniably useful trait. We would be able to see a variety of things outside of our normal visual range and we would actually have integrated night vision. As Tian explained to the cell:

Humans have tried to develop new technologies to enable capabilities beyond our natural capabilities. The visible light perceived by the natural vision of the human being occupies only a very small part of the electromagnetic spectrum. Electromagnetic waves longer or shorter than our visible light carry much more information … Depending on the material, an object may also have distinct NIR absorption and reflection. We were unable to detect this information to the naked eye.

Another interesting thing about this potential improvement is that it would not force a person to wear heavy, energy-consuming equipment, such as the aforementioned night vision goggles. This does not require any genetic manipulation. The army will most likely be interested in this work.

Dayong Jin of the School of Physical and Mathematical Sciences at the Sydney University of Technology has described the new work as "very innovative and inspiring." Dayong, who did not participate in the study, said that to his knowledge, "This work is the first demonstration of implantable and" portable "optical nanodevices. He stated that it was important that no inflammation or cell death was observed in the mice, but it is possible that some cells sucked the nanoparticles, a prospect that "deserves some investigation." more careful. "

Similarly, Kefalov was impressed by the research, claiming that "the authors did a remarkable job in characterizing the effects of injecting infrared-sensitive nanoparticles on the visual function of the mice," adding that "This innovative work demonstrates an ingenious and powerful method to improve the visual system's ability to detect light beyond the natural visible range." He thought it was "amazing" that the nanoparticles did not seem to interfere with the normal functioning of photoreceptors in visible light.

Whether the technique could be used to correct a visual impairment, such as color blindness, is less clear, he said.

"Since the method relies on the innate ability of photoreceptors to detect and amplify light signals, this approach to overcome the impaired function of photoreceptors will require the development of additional steps beyond the detection of light. outside the visible range, "Kefalov told Gizmodo.

In the future, Tian and Gang would like to improve the technique with organic-based nanoparticles composed of FDA-approved compounds, which could enable even more brilliant infrared vision. They would also like to modify the technique to make it more sensitive to human biology. Optimistic about the direction of this technology, Tian and Gang have already claimed a patent application related to their work.

I can already imagine TV commercials: "Ask your doctor if near-infrared vision is right for you".

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