It certainly sounds like something from a new sci-fi series, but a power-free set of contact lenses impregnated with nanoparticles has proven successful in allowing humans to see what has previously been invisible – even when their eyes are closed.
In a previous study, researchers at the University of Science and Technology of China demonstrated how injecting nanoparticles into the retinas of mice allowed them to see in the near-infrared range (NIR). This is a range of light not normally detectable by mammals, which tends to cap out beneath to 700-nanometer (nm) wavelength. NIR light travels in wavelengths between 700 nm and 2,500 nm and while it can be felt as heat, we can't see it.
Looking to see if they could develop a less invasive way of allowing visual access to NIR light, the UST researchers developed contact lenses based on the same technology used in the injections. That is to say that they embedded gold and sodium gadolinium fluoride nanoparticles doped with ytterbium and erbium ions into the lenses. These nanoparticles exert various effects on light, but the overall impact is that together, they are able to absorb NIR wavelengths and turn them into visible wavelengths in the 400-700 nm range through a process known as upconversion. The particles do this based on their structure and therefore do not need a power source to function.
The researchers first tested the lenses on mice. They found that mice wearing the lenses chose to avoid a box flooded with infrared light, instead choosing to move to a completely dark box. But mice who weren't wearing the lenses didn't show a preference between the boxes.
Next, in human trials, lens wearers were able to detect a Morse code pattern from pulsed infrared signals. Perhaps most interestingly, they were able to better perceive the signals when their eyes were closed. That's because when their eyes were closed, they didn't get interference from visible light and could instead focus on the NIR pulses, which are able to penetrate the eyelid.
The researchers further tweaked the nanoparticles in the lenses to convert certain NIR wavelengths to different colors. Those in the 980-nm wavelength were converted to blue light, those in the 808-nm wavelength became green, and those above 1,532 nm were converted to red light. Not only could this help wearers of the lenses get a better picture of their surroundings, but the team says it could also help color blind people overcome their visual restrictions.
Another step in the study was to develop a set of glasses that could be combined with the lenses to provide even finer detail than with the lenses alone.
Currently, the lenses can only perceive NIR light sent from LED sources, but the team is working on expanding their capabilities.
"Our research opens up the potential for noninvasive wearable devices to give people super-vision," says senior author Tian Xue, a neuroscientist at the University of Science and Technology of China. "There are many potential applications right away for this material. For example, flickering infrared light could be used to transmit information in security, rescue, encryption or anti-counterfeiting settings."
The contacts have been described in a paper published in the journal Cell.
Source: Cell Press via Phys.org
