The humble but useful and sticky cellophane tape. (Technically, it’s cellulose-acetate tape and is sometimes called “Scotch” tape, though that’s a trademarked name that belongs to 3M.)
Already handy for a wealth of purposes — sealing envelopes, wrapping holiday gifts, repairing ripped pages in books — cellophane tape has a unique property that makes it ideal for collecting droplet-sized water samples: when exposed to moisture, it curls up. That’s because the cellulose-acetate side absorbs water, while the sticky, adhesive-coated side repels water.
By using a laser to cut strips of tape into half-centimeter-long “fingers,” researchers at Purdue University have found they can create a material that — when exposed to water — turns into a tiny robotic claw capable of capturing droplets of water.
They also used the laser to machine the tape to 1/10th of its original thickness, which enhanced the curling action in water. The researchers then coated the graspers with magnetic nanoparticles, allowing the tiny claws to be easily gathered from water with a magnet.
“Say you were sampling for certain bacteria in water,” said Babak Ziaie, a professor of electrical and computer engineering and biomedical engineering. “You could drop a bunch of these and then come the next day and collect them.”
Eventually, the tape-based claws could also be adapted to attract specific biochemicals or bacteria, making them even “smarter” for environmental testing.