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"This film is light, flexible and easy to manufacture," he said. "It creates many new possible applications for circularly polarized light, of which cancer detection is just one."
Another key advantage is the film's stretchability. Light stretching causes precise, instantaneous oscillations in the polarization of the light that's passed through it. This can change the intensity of the polarization, alter its angle or reverse the direction of its spin. It's a feature that could enable doctors to change the properties of light, like focusing a telescope, to zero in on a wider variety of particles.
To make the film, the research team started with a rectangle of PDMS, the flexible plastic used for soft contact lenses. They twisted one end of the plastic 360 degrees and clamped both ends down. They then applied five layers of reflective gold nanoparticles—enough particles to induce reflectivity, but not enough to block light from passing through. They used alternating layers of clear polyurethane to stick the particles to the plastic.
"We used gold nanoparticles for two reasons," said Yoonseob Kim, a graduate student research assistant in chemical engineering. "First, they're very good at polarizing the kind of visible light that we were working with in this experiment. In addition, they're very good at self-organizing into the S-shaped chains that we needed to induce circular polarization."
Finally, they untwisted the plastic. The untwisting motion caused the nanoparticle coating to buckle, forming S-shaped particle chains that cause circular polarization in light that's passed through the plastic. The plastic can be stretched and released tens of thousands of times, altering the degree of polarization when it's stretched and returning to normal when it's released over and over again.
A commercially available device is likely several years away. Kotov also envisions the use of circularly polarized light for data transmission and even devices that can bend light around objects, making them partially invisible. U-M is pursuing patent protection for the technology.
The study, "Reconfigurable chiroptical nanocomposites with chirality transfer from the macro- to the nanoscale," was funded by the National Science Foundation (grant number ECS-0601345) and the U.S. Department of Defense.
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