Posted on Sep 02, 2019, 6 p.m.
Popular characteristics of movie superheroes are merely unrealistic flights of fancy, or are some of them more attainable such as night vision?
Scientists have used nanoparticles to confer one of these superpowers into an ordinary mouse, and gave it the ability to see near infrared light, which may one day be able to be applied to humans. Results of this research will be presented at the American Chemical Society Fall National Meeting & Exposition in 2019.
"When we look at the universe, we see only visible light," says Gang Han, Ph.D., the project's principal investigator, who is presenting the work at the meeting. "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."
Human eyes can detect light between the wavelengths of 400-700 mn; NIR light has longer wavelengths of 750-1.4 micrometers. Thermal imaging can help people to see in the dark by detection NIR radiation being given off by objects or organisms. The researchers wondered if injecting upconversion nanoparticles into the eyes of mice could give the animals NIR vision. These UCNPs can convert low energy photons from NIR light into higher energy green light that mammalian eyes are able to see.
The University of Massachusetts Medical School researchers targeted UCNPs to photoreceptors in the animals' eyes by attaching a protein that binds to sugar molecules in the photoreceptor surface to be injected behind the retina; several behavioral and physiological tests were conducted to determine if the animals could see and mentally process NIR light.
In one such test mice were trained to swim towards a visible light shaped in a triangle which marked an escape route with a similar light shaped in a circle marking a route without a platform, then the visible lights were replaced with NIR 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," says Han.
The UCNPs persisted in the animal’s eye for at least 10 weeks and was not observed to have caused any noticeable side effects. However the team will be working to improve safety and sensitivity of the nanomaterials before moving onto human trials. The team is developing UNCPs made of two organic dyes rather than rare earth elements. These organic nanoparticles emit green or blue light, and would have fewer regulatory hurdles.
"The UCNPs in our published paper are inorganic, and there are some drawbacks there," Han says. "The biocompatibility is not completely clear, and we need to improve the brightness of the nanoparticles for human use. We've shown that we can make organic UCNPs with much improved brightness compared with the inorganic ones."
“If we had a super dog that could see NIR light, we could project a pattern onto a lawbreaker's body from a distance, and the dog could catch them without disturbing other people," Han says. “We're actually looking at how to use NIR light to release a drug from the UNCPs specifically at the photoreceptors.”
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