By injecting nanoparticles into the eyes of mice, scientists gave them the ability to see near-infrared light—a wavelength not normally visible to rodents (or people). It’s an extraordinary achievement, one made even more extraordinary with the realization that a similar technique could be used in humans.
Of all the remarkable things done to mice over the years, this latest achievement, described today in the science journal Cell, is among the most sci-fi.
A research team, led by Tian Xue from the University of Science and Technology of China and Gang Han from the University of Massachusetts Medical School, modified the vision of mice such that they were able to see near-infrared light (NIR), in addition to retaining their natural ability to see normal light. This was done by injecting special nanoparticles into their eyes, with the effect lasting for around 10 weeks and without any serious side effects.
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Drops of fluid containing the tiny particles were injected directly in their eyes, where, using special anchors, they latched on tightly to photoreceptor cells. Photoreceptor cells—the rods and cones—normally absorb the wavelengths of incoming visible light, which the brain interprets as sight. In the experiment, however, the newly introduced nanoparticles upconverted incoming NIR into a visible wavelength, which the mouse brain was then capable of processing as visual information (in this case, they saw NIR as greenish light). The nanoparticles clung on for nearly two months, allowing the mice to see both NIR and visible light with minimal side effects.
Graphical representation of the process in action. When infrared light (red) reaches a photoreceptor cell (light green circle), the nanoparticles (pink circles) convert the light into visible green light.
Image: Cell
Essentially, the nanoparticles on the photoreceptor cells served as a transducer, or converter, for infrared light. The longer infrared wavelengths were captured in the retina by the nanoparticles, which then relayed them as shorter wavelengths within the visible light range. The rods and cones—which are built to absorb the shorter wavelengths—were thus able to accept this signal, and then send this upconverted information to the visual cortex for processing. Specifically, the injected particles absorbed NIR around 980 nanometers in wavelength and converted it to light in the area of 535 nanometers. For the mice, this translated to seeing the infrared light as the color green. The result was similar to seeing NIR with night-vision goggles, except that the mice were able to retain their normal view of visible light as well.
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Looking ahead, Tian and Gang would like to improve the technique with organic-based nanoparticles comprised of FDA-approved compounds, which could result in even brighter infrared vision. They’d also like to tweak the technique to make it more responsive to human biology. Optimistic of where this technology is headed, Tian and Gang have already claimed a patent application related to their work.
I can already imagine the television commercials: “Ask your doctor if near-infrared vision is right for you.”
