Magnetic tweezers move DNA molecules.

Denis Wirtz switches on his magnetic tweezers, grabs hold of a single DNA molecule, and uses a joystick to steer it carefully through a solution. Wirtz. assistant professor of chemical engineering, Johns Hopkins University, Baltimore, Md., is not playing an electronic game. He is manipulating molecules in groundbreaking research that could lead to new surgical tools and drug delivery systems. Using the device. a physician soon may magnetically move a microscopic sac filled with cancer-killing medicine through a patient's veins, then empty it directly into diseased cells.

"You could use these magnetic tweezers to transport a vesicle or fluid-filled cell containing a drug," Wirtz explains. You could use the tweezers as sort of a surgical tool to take it to the targeted area and then penetrate the diseased cells. It could be done very easily. Right now, you can move things inside a vein mechanically, but it's very invasive. With magnetic force, it's non-invasive."

The forces that allow the device to work are familiar to any child who has played with a magnet. If you place a sheet of paper over a steel button, then hold the magnet on top of the paper.. you can move the button without touching it. Wirtz's magnets are three sets of coiled copper wire, each connected to a power source. The coils are positioned to produce...