Flexible film may lead to smartphone-sized cancer detector

WASHINGTON: A thin, stretchable film that coils light waves like a Slinky could lead to a portable smartphone-sized device for more precise, less expensive monitoring for cancer survivors, scientists say.

The film provides a simpler, more cost-effective way to produce circularly polarised light, an essential ingredient in the process that could eventually provide an early warning of cancer recurrence.

"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," said Nicholas Kotov of the University of Michigan.

Circular polarisation coils light into a 3D helix that can spin in either a clockwise or counter-clockwise direction. It is invisible to the naked eye, and is rare in nature.

Large, expensive machines are required to generate circularly polarised light. Kotov believes the new film could provide a simpler, less expensive way to induce polarisation.

The detection process identifies biomarkers - bits of protein and snippets of DNA - that are present in the blood from the earliest stages of cancer 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 polarised 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 polarised light.

The film could be used to make a portable smartphone-sized device that could quickly analyse blood samples, Kotov said.

Another key advantage is the film's stretchability. Light stretching causes precise, instantaneous oscillations in the polarisation of the light that is passed through it.

This can change the intensity of the polarisation, alter its angle or reverse the direction of its spin.

It is 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.

Finally, they untwisted the plastic. The untwisting motion caused the nanoparticle coating to buckle, forming S-shaped particle chains that cause circular polarisation in light that is passed through the plastic.

The plastic can be stretched and released tens of thousands of times, altering the degree of polarisation when it is stretched and returning to normal when it is released.

The research was published in the journal Nature Materials.