Nano-camera lens reveals the hidden mirror world of molecules

A new kind of camera lens is illuminating a hidden mirror world by revealing the “handedness” of light in the pictures it takes. The lens could one day be used to sort helpful drugs from their potentially dangerous mirror versions.

Many molecules come in two different types, a left-handed and a right-handed version. Although both types contain the same atoms, they are arranged as mirror images of each other and can have different chemical properties. Biological molecules like amino acids seem to favour a certain handedness, though we don’t know why.

Sometimes this mirror world can cause problems. For instance, the drug thalidomide was prescribed in the 1950s and 60s as a cure for morning sickness, but withdrawn after it was realised that the right-handed version led to birth defects. That makes it important to be able to tell twin molecules apart.

On the one hand…

One way to identify molecules with mirror versions – a property known as chirality – is to look at how they scatter light waves. The handedness is imprinted on the direction the waves vibrate, or their polarisation. But current techniques for measuring polarisation involve using multiple lenses and other optical elements like beam-splitters and filters, which can degrade the image quality.

Now Reza Khorasaninejad of Harvard University and his colleagues have come up with a single nanotechnology lens that can do the same job. The lens is made from a layer of titanium dioxide that has been etched by a beam of electrons into rows of pillars just 600 nanometres high, sitting on top of an ordinary sheet of glass.

In a row, each rectangular pillar is at an angle to the one before it, so that the orientation of the pillars along the line seems to rotate clockwise or anticlockwise. Alternating rows twist in opposite directions, creating two side-by-side images without the need for bulky optics. “We have huge control over the light shaping,” says Khorasaninejad. “The weight, size and compactness of the structure is very small.”

To test out the lens, the team took a picture of a Chrysina gloriosa, a beetle whose shell is known to reflect left-handed light (above). In the future, Khorasaninejad says they hope to improve the resolution of the lens to let them pick out left- from right-handed molecules, making it useful for developing safe drugs.

Journal reference: Nano Letters, DOI: 10.1021/acs.nanolett.6b01897