September 2001

No More Needles?

By Technology Review

To free diabetics from daily pinprick tests, a startup called Sentek Group has come up with a new, noninvasive way of monitoring diabetes that doesn't require any pricey machinery. The Pittsburgh-based company has developed a cheap, disposable contact lens that hides behind the lower eyelid and changes color according to the glucose level of the tear fluid. Too much sugar, and the entire lens turns red; too little and it turns violet (photo). A patient matches the lens hue to a calibrated color wheel inside a compact mirror, with each shade corresponding to a glucose level.

Chemist Sanford Asher at the University of Pittsburgh created the material-a porous gel embedded with charged polystyrene particles. The nanometer-sized balls form a lattice that expands and contracts with the hydrogel. Sentek infuses lenses made from this gel with protein molecules that bind to glucose in tear fluid and cause the lens to swell. As the spacing in the polystyrene lattice changes, the material diffracts light at different wavelengths to produce a color change. Sentek hopes to have a product ready for human testing by late 2002.