A thin, stretchable film that is able to coil light waves like a Slinky could one day lead to more precise, less expensive monitoring for cancer survivors. The University of Michigan (U-M) chemical engineers who developed the film say it could help patients get better follow-up treatment with less disruption to their everyday lives.

The film provides a simpler, more cost-effective way to produce circularly polarized light, which is a central component of a novel technique for detecting the recurrence of cancer. The film is detailed in a paper published online in Nature Materials.

"More frequent monitoring could enable doctors to catch cancer recurrence earlier, to more effectively monitor the effectiveness of medications and to give patients better peace of mind. This new film may help make that happen," said Nicholas Kotov, professor of engineering at U-M.

Circular polarization is similar to the linear version that's common in things like polarized sunglasses. But instead of polarizing light as a two-dimensional wave, circular polarization coils it into a three-dimensional helix shape that can spin in either a clockwise or counterclockwise direction.

Circular polarization is invisible to the naked eye and is rare in nature, which is why it’s being employed in an up-and-coming cancer detection technique that can spot telltale signs of the disease in blood samples. Currently in the research stage, the process requires large, expensive machines to generate the circularly polarized light. Kotov believes the new film could provide a simpler, less expensive way to induce polarization.

The detection process identifies biomarkers such as bits of protein and snippets of DNA that are present in the blood from the earliest stages of cancer recurrence. It utilizes synthetic biological particles that can bind to these biomarkers. These particles are coated with a reflective layer that responds to circularly polarized light and added to a small blood sample from the patient. Clinicians can then see whether the reflective particles bind to the cancer biomarkers by examining the sample under circularly polarized light.

Kotov envisions that the film could be used to make a portable smartphone-sized device that could quickly analyze blood samples. These devices could be used by doctors, or potentially even at home.

"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."

"This film is light, flexible and easy to manufacture. It creates many new possible applications for circularly polarized light, of which cancer detection is just one."Nicholas Kotov, University of Michigan

Another key advantage is the film's stretchability, as stretching can cause precise, instantaneous oscillations in the polarization of the light passing through the film. 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 polydimethylsiloxane (PDMS), the flexible plastic used for soft contact lenses. They twisted one end of the plastic by 360° and clamped both ends down. They then applied five layers of reflective gold nanoparticles – enough to induce reflectivity but not enough to block light from passing through. Next, they used alternating layers of clear polyurethane to stick the particles to the plastic.

Finally, they untwisted the plastic. The untwisting motion caused the nanoparticle coating to buckle, forming S-shaped particle chains that induce circular polarization in light passing 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.

"We used gold nanoparticles for two reasons," explained 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."

A commercially available device is likely several years away. Kotov also envisions using the film to produce 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.

This story is adapted from material from the University of Michigan, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.