Abbott's group oriented liquid crystals to produce an image that would be viewed by the user but did it in a different way. In this case, a change in surface topography, not an applied electrical field, directs the orientation.

The researchers set an experimental goal: to create a liquid crystal assay that would report whether an antibody -- a molecule like those produced by the human body in response to an infection -- was present in a test sample.

First the researchers spread an ultrathin layer of gold atop an inch-square glass plate, creating a microscopic landscape of gentle, parallel hills and valleys.

Within that landscape they placed a field of molecular receptors with a particular affinity for the target antibodies. Now the assay was built.

Then the sample solution was poured over the assay. The molecular receptors grabbed the antibodies and held tight. When the solution ebbed away, the landscape was left irreversibly changed: It was studded with antibodies, like big boulders.

Finally, a few drops of liquid crystal were oozed across the landscape and allowed to settle.

Had there been no antibodies in the test solution -- no boulders -- the liquid crystal molecules would have aligned in parallel along the hills and valleys. In that orientation, they would have transmitted no light. The tester would have seen just a black square.

But because there were antibodies, the liquid crystals were forced to bend around them. Light caromed crazily through the these contorted crystals, creating psychedelic patterns of yellow, orange and red, or fluorescent pink and green.

"It was striking," Abbott said, recalling his first sight of the finished test. "It was an exciting result, because it was so clear-cut that it would have been understood by any onlooker."

"What the Davis group has done is very, very clever," said Curtis Fr
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Contact: Nicholas Abbott
nlabbott@ucdavis.edu
530 752 6527
University of California - Davis
26-Mar-1998