Photons keep out! Microscopic cages could soon be built with nanowire bars that block light from entering or exiting, while letting liquids and gases flow through.

It’s easy to shield an object from light – just stick it in a box. But if you want to access the contents at the same time, light will find a way through any holes you make. That’s a problem for proposed medical techniques that use carefully targeted light to control drug release.

Now Ali Mirzaei of the Australian National University in Canberra and his colleagues think they have a solution, which they call optical metacages.


Previous research has shown that nanowires – which are just billionths of a metre thick – can absorb and scatter light in unusual ways. The team ran a computer simulation of a wire 200 nanometres wide made from gallium arsenide coated with silver and another layer of gallium arsenide, and found it could absorb light from up to 100 nanometres away from its edges.

Making cages

By placing such wires at regular intervals, they were able to simulate cages that prevented light getting in or out, including one in the shape of Australia to show they could take on any shape.

If you tried to look inside one of these cages, you would only see a grey homogenous outer wall, says Mirzaei. But because there are physical gaps between the wires, small objects can pass through.

The team still needs to overcome some hurdles to build a real working cage, but the theory suggests the technique should work – and it may have biomedical applications.

“This gives us a great opportunity to protect and shield systems such as live cells inside the metacages from outside radiation, while gases and liquids can pass through it to feed them and get the chemical products out,” says Mirzaei.

Journal reference: to appear in Physical Review Letters

(Image credit: Australian National University)