Jan 18 2016
Chemical engineers from the University of Michigan have developed a stretchable, thin film that could help to provide improved follow-up treatment for cancer survivors.
The film coils light waves, like a slinky, and may lead to less expensive and more accurate examinations for cancer survivors with less interference with their everyday routine.
The film is used to develop circularly polarized light in a cost-effective and simple manner. This light is an essential ingredient in the process that could provide an early warning of the recurrence of cancer. A detailed description of the film has been published in the journal, “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.
Nicholas Kotov, Professor of Chemical Engineering
Instead of polarizing light in a two-dimensional wave, like the linear version that is common in polarized sunglasses, circular polarization coils light to form a three-dimensional helix shape, capable of spinning in a counterclockwise or clockwise direction.
Circular polarization is rare in nature, and cannot be seen by the naked eye. This enables circular polarization to be used in an up-and-coming cancer detection process that is hoping to be able to spot telltale signs of cancer in blood. At present this process is in the research stage, it requires expensive and large machines to create the circularly polarized light. Kotov believes that the new film could be a less expensive and simpler method to induce polarization.
The presence of biomarkers - small pieces of DNA and protein - in the blood are identified during the detection process, and they can be present in the blood from the earliest stages of cancer recurrence. The first step is to develop synthetic biological particles that attract the biomarkers. A reflective layer is used to coat these particles, and it responds to light that is circularly polarized. These particles are added to the patient’s blood sample. The reflective particles attach to the natural biomarkers, and this is seen when the sample is examined by the clinicians under the polarized light.
Kotov hopes to use the new film to develop portable smartphone-sized devices for quick analysis of blood samples. The devices could be used at home or even by doctors.
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, Professor of Chemical Engineering
Stretchability is another advantage to the film, light stretching causes instantaneous and exact oscillations in the polarized light that is passed through it. This will cause changes in the polarization’s intensity, reverse its spinning direction or adjust its angle. This feature will enable doctors to alter the properties of light, like adjusting the focus of a telescope, to zero in on a wider range of particles.
The film developing process started with a rectangle of flexible fabric called PDMS, often used for soft contact lenses. One end of the flexible plastic was twisted at 360 degrees and then both the ends were clamped down. Five layers of reflective gold nanoparticles were then applied to induce reflectivity, though not sufficient to block the passing of light. Alternating layers of clear polyurethane were used to attach the particles to the flexible plastic.
We used gold nanoparticles for two reasons. 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.
Yoonseob Kim, Graduate Student, Research Assistant in Chemical Engineering
The team finally untwisted the plastic, and this motion lead to the buckling of the nanoparticle coating. The motion also formed a S-shaped particle chain, leading to circular polarization in the light passing through the plastic. The flexible nature of the plastic allows it to be stretched and released tens of thousands of times. The polarization degree is altered when the plastic is stretched and returned to its normal form, over and over again.
Kotov aims to use circularly polarized light for devices that are capable of bending light around objects, thus making them invisible only partially. Kotov also intends to use this polarized light for data transmission. Patent protection for this new technology is being pursued by U-M.
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.