Nanoparticles give mice near-infrared vision

Technology News | March 4, 2019

By Rich Pell

Test and Measurement Materials & processes Medical Electronics Displays & Interfaces Sensing / Conditioning Optoelectronics Wearables

In their study, the researchers injected the retinas of mice with nanoparticles that bound to photoreceptors (image) – cells in the eye’s retina consisting of rods and cones that respond to light – and which then converted near-infrared light to green light that the animals could see. Their findings, say the researchers, could lead to advancements in human infrared vision technologies, including potential applications in civilian encryption, security, and military operations.

Compared to visible light (ranging from 400 to 700 nm), infrared has a longer wavelength. Due to physical limitations, say the researchers, no mammalian photoreceptor can effectively detect NIR light that exceeds 700 nm, and mammals are unable to see NIR light and to project a NIR image to the brain.

“The visible light that can be perceived by human’s natural vision occupies just a very small fraction of the electromagnetic spectrum,” says senior author of a paper on the study Tian Xue of the University of Science and Technology of China. “Electromagnetic waves longer or shorter than visible light carry lots of information.”

For example, people, animals, and objects emit infrared light as they give off heat, and objects can also reflect infrared light. Being able to see this would be an advantage, and as a result, say the researchers, the development of miniature nanoscale devices and sensors designed to intimately interface with mammals – including humans – to give them abilities that do not exist naturally are of growing interest.

The researchers – led by Xue and Jin Bao at the University of Science and Technology of China as well as Gang Han at the University of Massachusetts Medical School – developed their nanoparticles to work with the eye’s existing structures.

“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,” says Han. “Because infrared wavelengths are too long to be absorbed by photoreceptors, we are not able to perceive them.”

The scientists made nanoparticles that were able to anchor tightly to photoreceptor cells and act as tiny infrared light transducers. When infrared light hits the retina, the nanoparticles capture the longer infrared wavelengths and emit shorter wavelengths within the visible light range, at which point 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.

“In our experiment,” says Bao, “nanoparticles absorbed infrared light around 980 nm in wavelength and converted it into light peaked at 535 nm, which made the infrared light appear as the color green.”

Mice that received the nanoparticle injections showed unconscious physical signs that they were detecting infrared light, such as their pupils constricting, while mice injected with only the buffer solution didn’t respond to infrared light. A single injection of nanoparticles in the mice’s eyes resulted in infrared vision for up to 10 weeks with minimal side effects, say the researchers, allowing them to see infrared light even during the day and with enough specificity to distinguish between different shapes.

“In our study, we have shown that both rods and cones bind these nanoparticles and were activated by the near infrared light,” says Xue. “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 color vision deficits.”

“In the future,” says Han, “we think there may be room to improve the technology with a new version of organic-based nanoparticles, made of FDA-approved compounds, that appear to result in even brighter infrared vision.”

For more, see “https://www.cell.com/cell/fulltext/S0092-8674(19)30101-1.”