Flexible film has potential in pocket-sized cancer detector

The team of chemical engineers at the University of Michigan in Ann Arbor has developed the film to have optical properties that, when combined with a labelling technique, they believe will be able to detect tell tale molecules associated with the early stages of tumour development.

The film, made from polymethylsiloxane (PDMS) treated with layers of a colloidal dispersion of 660nm-diameter gold nanoparticles whose electrons interact with electromagnetic fields, induces a phenomenon called circular polarisation in light passing through it.

Unlike the more familiar plane polarisation, used in sunglasses to block out light reflected from surfaces whose waves are oscillating in one direction, the direction of the waves in circularly polarisation light rotate in a helix as they propagate. The helix can proceed in a clockwise or anticlockwise direction, and stretching the film can alter the 'tightness' of the helix or reverse its direction in a controllable way.

“We used gold nanoparticles for two reasons,” said Yoonseob Kim, a graduate student working on the project. “First, they're very good at polarising the kind of visible light that we were working with. In addition, they're very good at self-organising into the S-shaped chains that we needed to induce circular polarisation.”