Nanoparticles give mice infrared vision

Infrared light is produced by hot objects. Normally we need a special camera to see it, because the rod and cone photoreceptors in the backs our eyes in the retina, are not sensitive to light of this colour. But now scientists in China have developed nanoparticles that can be injected into the eye where they glue themselves to the retina, absorb incoming infrared and spit out light we can see, effectively endowing the eye with infrared vision. Mariana Campos asked Tijmen Euser who is from the Nanophotonics Centre at the University of Cambridge and wasn’t involved in the research, to cast his eye - using normal light to see it - over the study...

Tijmen - In order to see infrared light it first must be converted to visible light and they found nanoparticles that can do this. So they applied nanoparticles that are able to absorb infrared light and convert this to visible light. They’ve injected these nanoparticles into the mice's eyes and they have shown that mice can indeed see the infrared light.

Mariana - And the particles they use they used, do they have a special coating or something?

Tijmen -Yes. Normally if you would inject the particles as they are into the mouse's body, it would be rejected immediately by the immune system and they would not bind to anything. So what they did specifically is that they made photoreceptor binding particles, so they introduced a coating which binds to the photoreceptors in the eye.

Mariana - How does the system work?

Tijmen - What these particles have to do is something quite special because they have to absorb a photon which has a low energy and they have to emit a visible photon which has a high energy. So this doesn’t work, because the energy has to come from somewhere. So, the trick that these particles use is they absorb two infrared photons, they combine it internally and they use the combined energy to emit a visible light photon. The experience of the mice would be that they would see both the visible light that is always there, so they would see a normal green light, but on top of that they would see this additional contribution of converted infrared light.

Mariana - I’m curious, how do they realise that the mice were seeing infrared?

Tijmen - They’ve done several tests. First they’ve looked at the cellular level to see if there is an electrical response of the photoreceptors. These are small cells in the retina that act as pixels, so to say, of an eye. As a second step they looked at the pupil response of the mice and you could indeed see that the pupil reacts. And as a final test they actually did tests where they show the mice different patterns and they tried to teach the mouse to do something in response to food.

Mariana - That’s good condition training.

Tijmen - Yeah.

Mariana - Does it last forever?

Tijmen - They have shown that the effect lasts up to 10 weeks and at some point it wears off. And the reason why it wears off is that at some point the body will start to recognise these particles as being foreign to the body.

Mariana - Why do you think they would do this to mice? Why create an organism that can see infrared?

Tijmen - I think the general technique is interesting, so being able to see infrared may have some applications. One application that they mention is that you might be able to have an overlay of information that is projected in the infrared onto your retina so this would be this augmented reality application. That’s one application that I think could be interesting at some point. Another application which is not specifically about converting infrared light, invisible light, would be if you convert light from one part of the physical spectrum to another part of the physical spectrum, and this might help in treating blindness.