Scientists have discovered a way to give ordinary rodents the ability to see infrared light. The experiments were led by two researchers in the U.S. and China: Tian Xue of the University of Science and Technology of China and Gang Han from the University of Massachusetts Medical School. The results of the study have now been published in the science journal Cell.
Like humans, rodents can only see about 380 to 740 nanometers within the visible spectrum. Shorter wavelengths, like ultraviolet, and longer ones, like near-infrared, are invisible to their eyes. The research focused on formulating special nanoparticles that convert near infrared light into a greenish visible light. Those nanoparticles were then injected into the eyes of the rodents.
The nanoparticles clung on to photoreceptor cells in the rodents’s eyes, allowing them to turn low-energy, invisible protons, like near-infrared light, to high-energy ones that they could see. Testing of their electrical brain activity during infrared experiments showed that their eyes were functioning as though they were seeing visible light.
The researchers also has the rodents perform a number of activities to determine if their eyes were picking up infrared light. In one activity, the rodents were trained to escape a Y-shaped water maze using a hidden platform illuminated by infrared light. The modified rodents were able to detect the hidden platform, while the non-injected ones made their choices in what appeared to be a random way.
Another activity involved two connected boxes, one of which was completely dark while the other was bathed in infrared light. Rodents generally prefer the dark, and the non-injected rodents acted typically by showing no preference between the dark compartment and the one lit with infrared light. The modified rodents avoided the infrared light compartment, suggesting they saw it as being lit up.
According to the researchers, the rodents were able to detect near-infrared light, as well as normal light, for about 10 weeks without any obvious negative effects. Some rodents developed cloudy corneas after being injected with the nanoparticles, but those cleared up after a couple of weeks. The scientists hope that the technique could one day be used on humans.