Humans with “supervision” could be on the horizon after the development of an eye jab that enables seeing infrared light.
The single injection of nanoparticles bestowed the world of this particular electromagnetic radiation on mice – for up to ten weeks.
It worked both during the day and at night – and with enough specificity to distinguish between various shapes.
The breakthrough has potential applications for humans – including civilian encryption, security and military operations.
Seeing near infrared light directly would mean army personnel on dangerous missions would no longer need to wear cumbersome night vision goggles.
It may also lead to a revolutionary cure for people who are born colour blind, say the US and Chinese team.
In the study the injectable particles bound to photreceptor cells known as rods and cones.
This led to the mice developing infrared vision – without compromising their normal sight.
Senior author Professor Tian Xue, of the University of Science and Technology of China, said: “In our study, we have shown both rods and cones bind these nanoparticles and were activated by the near infrared light.
“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 colour vision deficits.”
Aside from a few animals – like pythons and vampire bats – infrared vision is beyond most creatures.
Humans and other mammals are limited to seeing a range of wavelengths known as visible light, which includes those of the rainbow.
But infrared radiation, which has a longer wavelength, is all around us.
People, animals and objects emit infrared light as they give off heat, and objects can also reflect it.
Thermal and infrared cameras are used in a wide range of industries – from security settings to identify intruders to construction to detect flaws in a building.
If humans could see infrared light, motorists could avoid accidentally hitting pedestrians by seeing their heat signatures in the dark.
It would also make it easier to rescue disaster survivors trapped under rubble or snow.
Prof Xue, a life scientist, said: “The visible light that can be perceived by human’s natural vision occupies just a very small fraction of the electromagnetic spectrum.
“Electromagnetic waves longer or shorter than visible light carry lots of information.”
His multidisciplinary group created the nanotechnology to work with the eye’s existing structures.
Biochemist Prof Gang Han, of the University of Massachusetts, explained: “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.
“Because infrared wavelengths are too long to be absorbed by photoreceptors, we are not able to perceive them.”
The researchers made nanoparticles that could anchor tightly to photoreceptor cells and act as tiny infrared light transducers.
When the light hits the retina, they capture the longer infrared wavelengths and emit shorter wavelengths within the visible range.
The nearby rod or cone then absorbs the shorter wavelength and sends a normal signal to the brain, as if visible light had hit the retina.
Neuroscientist Dr Jin Bao, a member of Prof Xue’s lab, said: “In our experiment, nanoparticles absorbed infrared light around 980 nm (nanometres) in wavelength and converted it into light peaked at 535 nm, which made the infrared light appear as the colour green.”
The study published in Cell tested the nanoparticles in mice which, like humans, cannot see infrared naturally.
Mice that received the injections showed unconscious physical signs that they were detecting infrared light, such as their pupils constricting.
Peers injected with a placebo solution did not respond.
To test whether the mice could make sense of the infrared light, the researchers set up a series of maze tasks to show they could see it in daylight conditions, simultaneously with visible light.
In rare cases, side effects from the injections such as cloudy corneas occurred but disappeared within less than a week.
This may have been caused by the injection process alone because mice that only received injections of the dummy solution had a similar rate of these minor problems.
Other tests found no damage to the tissue’s structure after injecting the nanoparticles right into the retina.
This is the layer at the back of the eyeball that contains cells sensitive to light. These trigger nerve impulses that pass via the optic nerve to the brain, where a visual image is formed.
Current infrared technology relies on detectors and cameras that are often limited by ambient daylight and need outside power sources.
The researchers believe the bio-integrated nanoparticles are more desirable for potential infrared applications in civilian encryption, security and military operations.
Prof Han said: “In the future, we think there may be room to improve the technology with a new version of organic-based nanoparticles, made of FDA (Food and Drug Administration) approved compounds, that appear to result in even brighter infrared vision.”
The researchers also think more work can be done to fine tune the emission spectrum of the nanoparticles to suit human eyes, which utilise more cones than rods for their central vision compared to mouse eyes.
Added Prof Xue: “This is an exciting subject because the technology we made possible here could eventually enable human beings to see beyond our natural capabilities.”
Pic – Stock image