Rats with vision improved by nanotechnology have been able to see infrared light and visible light, reports a study published on February 28 in the journal Cell. A single injection of nanoparticles into the eyes of the mouse provided infrared vision for up to 10 weeks with minimal side effects, allowing them to see infrared light even during the day and with sufficient specificity to distinguish between different forms. These findings could lead to advances in human infrared vision technologies, including possible applications in civilian cryptography, security, and military operations.
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 while emitting heat, and objects can also reflect infrared light.
"The visible light that can be perceived by the natural vision of the human being occupies only a very small fraction of the electromagnetic spectrum," says senior author Tian Xue of the China University of Science and Technology. "Electromagnetic waves longer or shorter than visible light carry much information."
A multidisciplinary group of scientists led by Xue and Jin Bao of the University of Science and Technology of China and Gang Han of the University of Massachusetts Medical School have developed nanotechnology to work with existing structures in the eye.
"When light enters the eye and reaches the retina, rods and cones – or photoreceptor cells – absorb the photons with wavelengths of visible light and send corresponding electrical signals to the brain," says Han. "As the infrared wavelengths are too long to be absorbed by the photoreceptors, we are not able to perceive them."
In this study, scientists made nanoparticles that can anchor tightly to photoreceptor cells and act as small transducers of infrared light. When infrared light hits the retina, nanoparticles capture the longest infrared wavelengths and emit shorter wavelengths within the visible light range. The nearby rod or cone absorbs the shorter wavelength and sends a normal signal to the brain as if visible light had reached the retina.
"In our experiment, nanoparticles absorbed infrared light around 980 nm at wavelength and converted it into light with a peak of 535 nm, which made infrared light appear as green," says Bao.
The researchers tested the nanoparticles in mice, which, as humans, can not see the infrared naturally. The mice that received the injections showed unconscious physical signals that they were detecting infrared light, just as their pupils were contracting, whereas mice injected with buffer alone did not respond to infrared light.
To test whether mice could understand infrared light, the researchers set up a series of tasks in the labyrinth to show that mice could see infrared in daylight, simultaneously with visible light.
In rare cases, the side effects of injections, such as hazy corneas, have occurred but have disappeared in less than a week. This may have been caused only by the injection process, as the mice that received only injections of the buffer solution had a similar rate of these side effects. Other tests found no damage to the retinal structure after sub-retinal injections.
"In our study, we showed that both rods and cones bind to these nanoparticles and were activated by the near infrared light," says Xue. "Therefore, we believe that this technology will work in human eyes, not only to generate super vision, but also for therapeutic solutions in human red vision deficits."
Current infrared technology relies on detectors and cameras that are usually limited by daylight and need external power sources. Researchers believe that bio-integrated nanoparticles are most desirable for potential infra-red applications in civil cryptography, security, and military operations. "In the future, we think there may be room to improve technology with a new version of organic-based nanoparticles made from FDA-approved compounds that appear to result in even brighter infrared vision," says Han.
The researchers also believe that more work can be done to adjust the emission spectrum of the nanoparticles to suit human eyes, which use more cones than the stems for their central vision compared to the eyes of the mouse. "This is an exciting subject because the technology we make possible here could eventually allow humans to see beyond our natural capabilities," says Xue.
This study was supported by the Chinese Academy of Sciences' Priority Strategic Research Program, China National Research and Development Program, China National Natural Science Foundation, National Institutes of Health, UMass OTCV Award and Worcester Mel Foundation . Cutler Award and the Human Frontier Science Program.
Cell, Ma et al.: "Mammalian Near-Infrared Image Vision Through Inano and Nanoantennae Retinal Self-Powered". https://www.cell.com/cell/fulltext/S0092-8674(19)30101-1
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