Nanoparticles confer infrared vision

Astonishingly simple method could expand the human sense of sight

Using nanoparticles, the human sense of sight could soon be extended to the infrared. © Delpiuxart / iStock
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Extended senses: An injection with nanoparticles could in future expand our sense of sight - and make infrared radiation visible to us. How to do this, researchers have now successfully tested with mice. The nanoparticles injected into the eye attach themselves to the retinal photoreceptors and convert incident infrared radiation into green light signals. These are then processed by the eye as normal. According to the researchers, this method could also give us people a true infrared view.

Even though our eyes can even detect individual photons of light, our sense of sight is comparatively limited. Many animals have much sharper and faster eyes or they see invisible areas of electromagnetic radiation. Bats and many insects can see UV light, while other invertebrates record infrared radiation. By contrast, the human eye can only perceive wavelengths between 400 and 700 nanometers.

Why we can not see an infrared

The problem: The visual pigments of our eye can not convert other wave ranges into nerve signals. Especially with the long-wave infrared radiation, this has quite practical reasons: The infrared photons are relatively low energy. To perceive them, the visual pigments would have to develop significantly lower stimulation thresholds. However, this would mean that even spurious signals are registered more heavily - and many visual information is lost in the noise.

"This physical limitation means that no mammalian photoreceptor can detect infrared light of more than 700 nanometers wavelength, " said Tian Xue from the University of Science and Technology in Hefei and his colleagues. So far, man can compensate for this deficit only with technical aids - for example, by implanted electrodes, which are linked to a special camera.

Nanoparticles as light transducers

But now Xue and his team have discovered a method that could greatly enhance our sense of sight. For their study, they developed special nanoparticles that act like small light transducers: when they are irradiated with infrared light in the wavelength range of 980 nanometers, they emit visible light of 535 nanometers wavelength. The infrared radiation is thus converted into green visible light. display

The course of the study: Because the nanoparticles on the photoreceptors act as light transducers, mice can perceive infrared signals. Ma et al./Cell

The trick here: These nanoparticles are configured so that they attach to the natural photoreceptors of the mammalian eye. The injection of a saline solution containing these nanoparticles into the eye of mice showed that this works: "The particles anchored themselves to the inner and outer areas of the cones and stabs ", The researchers report. "There they formed a layer of built-in nano-antennas that converted the light."

Visual sense extended to the infrared

But is with these nanoparticles a true infrared view possible? To test this, the scientists performed a series of visual and behavioral tests on the mice. Among other things, these showed that the infrared light causes a pupil reflex in the treated mice - something that only takes place when the visual signals are transmitted to the brain. The mice's brainwave confirmed that the infrared radiation has been converted and processed into normal visual stimuli, the researchers report.

In another test, the animals were given the choice between a dark and an infrared lit cage. Untreated mice often opted for both options, but the treated animals avoided the infrared cage - they seemed bright and they did not like it. "This clearly demonstrates that the mice acquired an infrared sense and that they were actually able to see infrared light with our nano-antennas, " said Xue and his team.

One injection more than ten weeks infrared view

The mice were even able to recognize shapes with their new infrared sense of sight: The animals quickly learned that an infrared triangle leads to the food, but a circle does not. Important also: The additional infrared stimuli did not hinder the normal vision of the mice, as the experiments showed. "The infrared view works in parallel with the natural daylight vision, " say Xue and his team.

The injection of nanoparticles into the eye did not cause any damage to the retina, as the researchers report. Although some animals temporarily developed a slight clouding of the cornea, it disappeared after a few days on its own. Positive as well: a single injection of these nanoparticles was enough to give the mice an infrared sense of sight for more than ten weeks.

Could also work in humans

According to the scientists, this method offers a unique opportunity to expand the human visual sense. "We believe that technology works in the human eye as well, " says Xue. Because the photoreceptors and sensory physiology hardly differ in mouse and human. "That's pretty exciting, because it would allow us to expand our natural senses and develop 'super eyes, " "says Xue.

Among other things, researchers see applications in the security sector, in the military and in science - wherever already near-infrared signals are important as information carriers. But the nanoparticles could not only expand our sense of sight, they may also be suitable for the treatment of visual deficits such as color blindness, say Xue and his colleagues. They now want to work on further optimizing their nanoparticles and possibly even constructing them from already medically approved molecules. (Cell, 2019; doi: 10.1016 / j.cell.2019.01.038)

Source: Cell Press

- Nadja Podbregar