Injectable nanoparticles give mice infrared vision

The military and police sometimes spot people trying to hide by using cameras that detect the heat coming off their bodies. These devices work by detecting infrared light, which is emitted by hot objects. Scientists in the US and China wondered if there was a less bulky solution for such imaging. Their solution: biocompatible nanoparticles that can give animals (and potentially humans) the ability to see near IR light (Cell 2019 DOI: 10.1016/j.cell.2019.01.038). The downside? They require an injection in the eye.

“This research is just plain cool,” says Vince Rotello of the University of Massachusetts Amherst, who also works on integrating nanomaterials with biology but was not involved in the new study. Rotello points out that most nanomedical research focuses on curing disease rather than adding extra capabilities.

These injectable particles essentially convert near IR light into wavelengths that mice can see. Gang Han of the University of Massachusetts Medical School and coworkers designed sodium yttrium fluoride nanoparticles doped with ytterbium and erbium that specifically absorb wavelengths emitted by infrared LEDs and then emit wavelengths that could be picked up by the light-sensing cells inside a mouse’s eyes. Mice and humans can normally only see wavelengths of light between 380 and 740 nm. These nanoparticles absorb light at 980 nm.

Han’s group sent the particles to Tian Xue’s group at the University of Science and Technology of China in Shanghai, who injected the nanoparticles into the eyes of mice. Sugars on the outside of the nanoparticles bind to photoreceptor cells in the eye without harming them. Mice receiving the nanoparticle injections could see and navigate in rooms lit with visible light and in rooms with only infrared light. Han and Xue were surprised that the nanoparticles worked without needing to add anything more to the light-sensitive cells. The nanoparticles remained in place and functioning several months later.

Han also says that the nanoparticles can be easily modified to detect different wavelengths of light, such as longer infrared wavelengths for thermal imaging or visible light wavelengths to help counter colorblindness in people.