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