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Nanoparticles could grant humans permanent night vision

By Brooks Hays

Aug. 27 (UPI) -- Built-in night vision may not be far off. Scientists have developed nanoparticles that allow mice to see near-infrared light.

Researchers are scheduled to describe the technological breakthrough on Tuesday at 12:30 p.m. ET at the American Chemical Society's fall meeting, held this week in San Diego. Their presentation will be streamed live online.

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"When we look at the universe, we see only visible light," lead researcher Gang Han, a material scientists and biochemist at the University of Massachusetts Medical School, said in a news release. "But if we had near-infrared vision, we could see the universe in a whole new way. We might be able to do infrared astronomy with the naked eye, or have night vision without bulky equipment."

The eyes of humans and other mammals field optical light waves ranging in wavelength from 400 to 700 nanometers. Near-infrared light features wavelengths between 750 nanometers and 1.4 micrometers.

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To see in the dark, humans use thermal imaging cameras or goggles, which convert near-infrared light into optical wavelengths. The technology is big and bulky.

Han and his colleagues have designed a nanoparticle that performs the "upconversion" of near-infrared to visible light. The upconversion nanoparticles, UCNPs, turn low-energy photons into higher-energy green light.

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In the lab, scientists injected the nanoparticles, made from rare-earth metals, into the eyes of mice, just behind their retinas. A series of physiological and behavioral tests confirmed the night-vision abilities provided by the nanoparticles.

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Researchers trained mice to swim toward a visibly lit triangle where a shallow platform allowed them to get out of the water. A similarly lit circle led them down a flooded corridor without a platform. After the mice were properly trained, researchers replaced the visible triangle with a triangle lit by near-infrared light.

"The mice with the particle injection could see the triangle clearly and swim to it each time, but the mice without the injection could not see or tell the difference between the two shapes," said Han.

Han and his colleagues are currently working on similar nanoparticles made with organic dyes.

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"The UCNPs in our published paper are inorganic, and there are some drawbacks there," he said. "The biocompatibility is not completely clear, and we need to improve the brightness of the nanoparticles for human use."

Researchers plan to continue testing different types of nanoparticles to confirm their effectiveness and safety. In the most recent tests, the nanoparticles persisted for 10 days in the eyes of the mice models and did not cause any observable side effects.

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