Cyborg Eye

Injection of nanoparticles into the retina turns the visual organ into a thermal imager 

Maria Perepechaeva, "First-hand Science"

The spectrum of electromagnetic waves that the human eye perceives is relatively small – about 400-700 nm. Neither the ultraviolet radiation of the shorter wavelength region, nor the long-wave infrared radiation emitted by bodies with temperatures above absolute zero is available to us. However, the recent Sino-American development will partially make up for this evolutionary omission by expanding the visible spectrum range to near infrared.

The first link in the chain of events through which we see the world around us is the light falling on the retina of the eye, where the rods and cones, photosensitive photoreceptor cells are located. Sticks containing the photopigment rhodopsin make it possible to distinguish between black and white and are responsible for night vision. Each of the cones responsible for color vision contains one of three variants of the iodopsin photopigment, sensitive to red-orange, green or blue light.

Under the action of photons, photochemical reactions are triggered in a photosensitive cell: the energy of light turns into a nerve impulse, which "reports" what it sees to the visual center of the brain. But at the same time, our photopigments cannot be perceived as too high-energy photons of the ultraviolet spectrum, as well as too low-energy infrared ones. 

Attempts to expand the wavelength range perceived by the eye have been made before. For example, an infrared radiation sensor was placed on the head of laboratory rats, which was connected to the somatosensory zone (the center of touch) of the cerebral cortex of animals. Now scientists from the Chinese University of Science and Technology and the School of Medicine of the University of Massachusetts (USA) have developed a more physiological way to see infrared radiation by injecting special nanoparticles into the eyes.

In the work, nanoparticles based on erbium and ytterbium were used, capable of converting infrared light into visible light by absorbing photons at one wavelength and emitting at another (in this case, in the green spectrum, to which mammalian eye receptors are most sensitive). The nanoparticles were modified and coated with protein molecules that can bind to specific molecules on the membranes of photoreceptors of rods and cones. Then they were injected under the retina of laboratory mice, and the control group was injected with a buffer solution.

As it turned out, the injected nanoparticles were firmly bound to the photoreceptors of photosensitive cells, and side effects were common for such a procedure.

Unlike the control group, the experimental animals had pupils narrowed under the influence of infrared radiation, photocurrents in the retina were determined, and the visual cortex of the brain was activated.

The mice also behaved differently in behavioral tests. For example, when they were offered a choice of an ordinary dark room and with infrared "illumination", the control animals did not distinguish between them, and the experimental animals clearly preferred a dark room.

Then the subjects were offered a real intellectual exercise to determine how well they see in infrared light. The animals were launched into a complex water maze, the correct exit from which was marked with a triangle, and the wrong one with a circle. At first, these icons were illuminated with visible light, and all the mice learned to swim to the triangle even when the location of the labels changed. However, when replacing the visible illumination with infrared, the control mice were immediately lost, and the mice "with nanoparticles" confidently found a way out.

So, the application of nanotechnology has been very successful, despite the fact that visible light carries more energy than infrared, and nanoparticles need to absorb several infrared photons before emitting one photon of the visible spectrum. According to the developers, this technology is quite applicable to people, especially those professions in which it is difficult to do without infrared vision. After all, although special thermal imaging devices have been created today, they are not always convenient to use. 

But, probably, this technology can play an even greater role in helping people who lose their eyesight, including due to the death of photoreceptors as a result of age-related ophthalmological diseases.

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