Nanoparticles give mice infrared vision

Nanoparticles that can be injected into the eye to endow the retina with infrared vision have been developed by scientists in China...

Invisible to the naked eye, infrared light is nevertheless felt as heat, and we can see it with the aid of special infrared-sensitive cameras.

But now a team led by Yuqian Ma, from the University of Science and Technology of China, have created a new technology that gives mice 10 weeks of infrared vision with little side-effects.

“In order to see infrared light, it must first be converted to visible light,” explains Tijmen Euser, from the Nanophotonics centre at the University of Cambridge, who is not an author of the work. “They applied nanoparticles that are able to absorb infrared light and convert it to visible light [then] they have injected these nanoparticles into the mice eyes and have shown that the mice can, indeed, see infrared light.”

The process spans the fields of physics, chemistry and biology. The novel step was that the researchers coated the off-the-shelf nanoparticles with a molecular glue to enable them to attach to the light-sensitive photoreceptor "cone" cells in the retina.

Once in position, the nanoparticles absorb two photons of infrared light and combine their energies to produce a single photon of visible, green light. “The mice would see both the visible light that is always there, but on top of that, they would see this additional contribution of converted infrared light, and they would experience this as green light,” Euser explains.

To test that mice could, indeed, see infrared, the researchers measured the electrical response of the cells in their eyes, as well as their pupil responses, and, finally, performed a behavioural conditioning test where the animals received a food reward for responding to patterns of shapes shown to them. Crucially, the mice were trained using shapes displayed in visible light. Then the team switched to showing the shapes only in infrared and the animals continued to respond, proving that they could still see the presented shapes.

The possibilities arising from this research are many and varied, including treatment of some vision impairments, development of enhanced human vision for military applications, and human-machine interactions.

According to the study's co-author Tian Xue, "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. This is an exciting subject, because the technology we made possible here could eventually enable human beings to see beyond our natural capabilities."