Humans and other mammals are limited to seeing a range of wavelengths of light called visible light, which includes the wavelengths 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 infrared light. Now a team of researchers from the University of Massachusetts Medical School, the University of Science and Technology of China and China’s Center for Excellence in Brain Science and Intelligence Technology has developed technology to give night vision to mammals. A single injection of nanoantennae in the mice’s eyes bestowed infrared vision for up to 10 weeks with minimal side effects, allowing them to see near-infrared light even during the day and with enough specificity to distinguish between different shapes.

The visible spectrum is the portion of the electromagnetic spectrum that is observed by the human eye. A typical mammalian eye will respond to wavelengths from about 400 to 700 nm (nanometers).

However, this is only a small percentage of the full electromagnetic spectrum. The detection of longer wavelength light, such as near-infrared (NIR) light or infrared light, is impossible.

The human eye is unable to see NIR or to project an NIR image to the brain without the aid of complicated and cumbersome electronic devices, such as night vision goggles. During the day, these goggles become saturated and lose their ability to function.

“The visible light that can be perceived by human’s natural vision occupies just a very small fraction of the electromagnetic spectrum,” said study co-author Dr. Tian Xue, a researcher at the University of Science and Technology of China.

“Electromagnetic waves longer or shorter than visible light carry lots of information.”

“With this research, we’ve broadly expanded the applications of our nanoparticle technology both in the lab and translationally. These nanoantennae will allow scientists to explore a number of intriguing questions, from how the brain interprets visual signals to helping treat color blindness,” said Dr. Gang Han, from the University of Massachusetts Medical School.

In the study, the scientists developed lectin protein conjugated nanoparticles that can be delivered in droplets.

These proteins guide the nanoantennae and ‘glue’ them to the outside of retinal photoreceptors in mice. Once anchored on the cells, these microscopic antennae convert NIR into visible, green light.

The green light is observed by the retinal cell and images are sent and interpreted by the brain as visible light. This happens without the aid of complicated equipment.

The researchers also developed a series of tests to verify that the mice treated with the nanoparticles were fully capable of perceiving NIR light.

They demonstrated that mice injected with these nanoantennae can not only perceive NIR light, but also obtain NIR pattern vision and are even able to differentiate between sophisticated shape patterns such as triangles and circles.

Treated mice were able to perceive these light patterns even in daylight conditions, indicating that the nanoparticles were working in parallel with conventional vision.

Also, thanks to the close proximity of the nanoantennae and photoreceptors, an exceptionally low power NIR LED lamp light is sufficient to activate the nanoparticles.

After two weeks, the ability wore off and the nanoparticles left no lingering effects to the mice or their vision.

“We believe that this research is a major advance in the field of biotechnology. This concept-provoking study should pave the way to numerous critical applications via the unique creation of mammalian NIR visual ability and have high translational potential,” Dr. Han said.

“Moreover, it is very likely that the sky may look very differently both at night and in daytime. We may have the capability to view all the hidden information from NIR and IR radiation in the universe which is invisible to our naked eyes.”

The results were published in the journal Cell.

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Yuqian Ma et al. Mammalian Near-Infrared Image Vision through Injectable and Self-Powered Retinal Nanoantennae. Cell, published online February 28, 2019; doi: 10.1016/j.cell.2019.01.038