Swell idea for a chemical sensor.

Swell idea for a chemical sensor 

Many scientists want to perfect miniature chemical sensors to detect small quantities of drugs, pollutants, oxygen or other substances in the environment or the body. Yet after a decade's work, few such devices have reached the marketplace. Now, two chemists have patented their ideas for what they call a cheap technology with many applications. The secret of their device: a swellable polymer, says Marian F. McCurley of the National Institute of Standards and Technology in Gaithersburg, Md.

The new sensor contains two optical fibers, one to carry light down to the sensing tip and the other to carry the reflected light back out. The sensing tip consists of a polymer lens specially made to react to the substance being monitored. A reflective film coats one side of this lens.

When the polymer detects its target chemical, its cross-linkages change. Depending on the particular chemistry between the two materials, the polymer either expands to let water in or shrinks. As the lens changes shape, it pushes the reflective film closer to or farther from the optical fibers, thereby changing the amount of reflected light.

Unlike most biosensors, this one isolates the light from the chemical components, and that means the system should last longer, says Kenneth D. Legg, president of Polysense, Inc., in Wellesley, Mass., which plans to develop the technology.