Contact lenses embedded with upconversion nanoparticles have enabled both humans and mice to perceive near-infrared light without implants or external power.
The lenses convert near-infrared (NIR) wavelengths into visible light and allow wearers to detect pulsed signals and spatial cues, even with their eyes closed. The research team characterized the optical properties of the lenses using UV–Vis–NIR spectroscopy and fluorescence measurements, which confirmed wavelength conversion and emission intensity.
Yuqian Ma, of the University of Science and Technology of China in Hefei, explained with colleagues that NIR light penetrates the eyelid better than visible light. Indeed, they found that visible light sensitivity decreased more than 200-fold when participants closed their eyes. When they closed their eyes in ambient daylight conditions, their sensitivity to NIR light increased 3.7-fold while sensitivity to visible light decreased 4.5-fold. In additional tests of upconversion contact lenses (UCLs), participants were able to perceive Morse-code-like infrared flashes; mice displayed both behavioral and physiological responses to infrared stimuli.
The “findings show the potential of UCLs for NIR-light information discrimination in both temporal and spatial dimensions in humans,” the authors wrote.
A trichromatic version of the lenses (tUCLs) further distinguished between different infrared wavelengths by converting them into red, green, and blue visible light. NIR light in the 800 nm to 1,600 nm range can penetrate biological tissues that are rich in water such as eyelids and corneas, the authors described. In tests of the tUCLs, participants were able to perceive and match NIR colors and discriminate letter sequences that were encoded by NIR color.
Finally, a series of reflective mirrors showed that participants with tUCLs were able to identify NIR colors that they would normally miss. Both images and letter patterns that were black and white in visible light were colorful in NIR light, when observed with the tUCLs and the wearable eyeglass system that the researchers also developed to overcome the scattering of visible light that altered the spatial information of NIR light before it could be perceived by the human eye.
“Our research opens up the potential for noninvasive wearable devices to give people super-vision,” said senior author Tian Xue in a press release. The technology could support future applications in surveillance, signaling, and spectral encoding, as well as enhancing vision in foggy, dusty, or otherwise poor visibility conditions. They could also be used with smart devices for rescue and emergency situations.
Still, detecting natural environmental NIR signals remains difficult without artificial illumination, the authors noted of their study’s limitations. Broader validation studies are needed to address generalizability of the limited sample size, and the researchers suggest improvements such as designing upconversion nanoparticles that emit light directionally aligned with incoming NIR light and embedding microscale optical fiber channels in UCLs to guide light directly to the eye.
The authors had no competing interests to declare.
Source: Cell