"It's the same thing you see in butterfly wings," Omenetto said. "The color is defined by nano-patterning of the surface. You monitor the color change, and the color change depends on whatever you have put inside the film." If the sensor detects E. coli, for example, the film would change colors to whatever color reflects the presence of the bacteria. If it's red, the film would turn red, as in a litmus test.
Omenetto has turned to a tough audience to test public acceptance of his work.
"I go to my kid's elementary school, and I bring a cocoon and a lens that is made from the cocoon's silk," he said. When they hold what appears to be an ordinary magnifying glass, made out of silk from the cocoon, "it's easy to capture their attention. It's kind of cool."
Progress in the research has come at a fast clip, due partly to funding from the Defense Department's Advanced Research Projects Agency. Films from silk could be used for many things of interest to the Pentagon, like foolproof personal identification. The researchers have fabricated 3-D holograms that could be embedded in an identification card, or for that matter, a personal credit card, revealing whether the person using the card is authorized to do so.
The researchers caution that it's too early in the program to know just where it will lead, but there's little doubt they think they are on to something big.
Food poisoning kills about 5,000 Americans every year, along with 76 million illnesses and 325,000 hospitalizations, according to federal statistics. It's also costly to producers. Spinach growers lost $350 million in the E. coli outbreak in 2006.
So it would be great if an edible sensor in the bag could tell you whether it's safe to eat the veggies. But to work, the researchers said, the sensor has to produce an instantaneous warning that is extremely clear (like turning red) and there is still work to be done there.
"I see a path forward," Omenetto said. "I wouldn't be doing this if there wasn't the hope of doing something useful in the end."
And, he said, it's what makes serendipitous science so rewarding.
"If I hadn't shared the hallway with David, I would never in a million years have thought of making optics out of silk."
Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.