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Night vision for human eyes could be possible after nanoparticle breakthrough

Image credit: Petr Taborsky | Dreamstime.com

Researchers from University of Massachusetts Medical School (UMMS) have been developing nanoparticles, tested successfully on mice, that could one day provide built-in night vision for humans.

As part of a study in February 2019, collaborating with scientists from the University of Science and Technology of China, the team injected nanoparticles into mice’s eyes, which bestowed infrared vision for up to 10 weeks with minimal side effects. This allowed them to see infrared light even during the day and with enough specificity to distinguish between different shapes.

The scientists, presenting their findings at the American Chemical Society (ACS) Fall 2019 National Meeting & Exposition yesterday (27 August), have now reported progress in making versions of these nanoparticles for human applications.

“When we look at the universe, we see only visible light,” said Gang Han, a PhD student at UMMS and the project’s principal investigator. “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 can detect light between the wavelengths of 400 and 700 nanometres (nm). On the other hand, near-infrared (NIR) light has longer wavelengths: 750nm to 1.4 micrometres. While thermal-imaging cameras can help people see in the dark by detecting NIR radiation given off by organisms or objects, these devices are bulky and inconvenient, posing a challenge for people using this technology.

To overcome this issue, Han and his colleagues considered whether they could give mice NIR vision by injecting a special type of nanomaterial - 'upconversion nanoparticles' (UCNPs) - into their eyes. These nanoparticles, which contain the rare-earth elements erbium and ytterbium, can convert low-energy photons from NIR light into higher-energy green light that mammalian eyes can see.

In their previous study, the researchers targeted UCNPs to photoreceptors in mouse eyes by attaching a protein that binds to a sugar molecule on the photoreceptor surface. They then injected the photoreceptor-binding UCNPs behind the retinas of the mice.

To determine whether the injected mice could see and mentally process NIR light, the team conducted several psychological and behavioural tests.

In one of the tests, the researchers placed the mice into a Y-shaped tank of water where one branch of the tank had a platform that the mice could climb on to escape the water. Here, the team trained the mice to swim towards visible light in the shape of a triangle, which marked the escape route. A similarly lit circle marked the branch without a platform.

The researchers then replaced the visible light with NIR light. Han observed: “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.”

Although the UCNPs persisted in the mice’s eyes for at least 10 weeks and did not cause any noticeable side effects, Han said he wants to improve the safety and sensitivity of the nanomaterials before the team try to test the nanoparticles on humans.

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

Instead of using rare-earth elements in their tests, the team is now experimenting with UCNPs made up of two organic dyes. “We’ve shown that we can make organic UCNPs with much improved brightness compared with the inorganic ones,” he said.

These organic nanoparticles can emit either green or blue light. Also, in addition to having improved properties, the organic dyes could also have fewer regulatory hurdles.

The team also has plans to test the technology on dogs as part of its project. “If we had a 'super-dog' that could see NIR light, we could project a pattern onto a lawbreakers’ body from a distance and the dog could catch them without disturbing other people,” Han enthused.

Furthermore, Han said that the nanoparticle technology could prove important for medical applications, such as treating diseases of the eye: “We’re actually looking at how to use NIR light to release a drug from the UNCPs specifically at the photoreceptors”.

On the subject of vision, scientists from University of California-San Diego and China’s Harbin Institute of Technology have worked together to develop a soft contact lens capable of changing its focal length at the signal of the wearer.

Furthermore, researchers from Stanford University have developed auto-focusing glasses to help those suffering from presbyopia, an eye condition that most people suffer from after the age of 45.

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