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Lines at the grocery store might become as obsolete as milkmen, if a new tag that seeks to replace bar codes becomes commonplace. Researchers from Sunchon National University in Suncheon, South Korea, and Rice University in Houston have built a radio frequency identification tag that can be printed directly onto cereal boxes and potato chip bags. The tag uses ink laced with carbon nanotubes to print electronics on paper or plastic that could instantly transmit information about a cart full of groceries. “You could run your cart by a detector and it tells you instantly what’s in the cart,” says James M. Tour of Rice University, whose research group invented the ink. “No more lines, you just walk out with your stuff.” RFID tags are already used widely in passports, library books and gadgets that let cars fly through tollbooths without cash. But those tags are made from silicon, which is more expensive than paper and has to be stuck onto the product as a second step.