A thin, stretchable polymer-based film that can coil light waves like a Slinky could make monitoring of cancer survivors more effective and less expensive. Developed by University of Michigan chemical engineering researchers, the film provides a simpler, more cost-effective way to produce circularly polarized light, part of a process that could eventually provide an early warning of cancer recurrence. The research is detailed in a paper published online in Nature Materials.
Circular polarization is similar to the linear version that's common in things like polarized sunglasses. But instead of polarizing light in 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 it's rare in nature. That makes it useful in an up-and-coming cancer detection process that looks to be able to spot telltale signs of the disease in the blood. Currently in the research stage, the process requires large, expensive machines to generate the circularly polarized light. Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering leading the research and an author of the paper, believes the new film could provide a simpler, less expensive way to induce polarization.
Researchers took a rectangle of PDMS, the flexible plastic used for soft contact lenses, twisting one end 360 degrees and clamping 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. Alternating layers of clear polyurethane were used to stick the particles to the plastic. Finally, the researchers untwisted the plastic. The untwisting motion causes 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.
One key advantage of the film is its stretchability, notes a press release distributed by the university. Light stretching causes precise, instantaneous oscillations in the polarization of the light that's passed 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 wide variety of particles.
The detection process identifies biomarkers that are present in the blood from the earliest stages of cancer's recurrence. It starts with synthetic biological particles that are made to be attractive to these biomarkers. The particles are first coated with a reflective layer that responds to circularly polarized light, then added to a small blood sample from the patient. The reflective particles bind to the natural biomarkers, and clinicians can see this when they examine 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 using the technique. The devices could be used by doctors, or potentially even at home, to monitor for the recurrence of cancer in patients who are in remission.
"This film is light, flexible and easy to manufacture," Kotov said in a prepared statement. "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." Kotov also foresees many other possible applications for circularly polarized light, including data transmission and even devices that can bend light around objects, making them partially invisible.