When a surgeon removes a tumor, some cancer cells may get left behind, threatening to seed another malignant growth. Researchers have just begun the first clinical trial of a new anticancer tool that they hope will kill these stubborn cells: a plasma scalpel.

The pen-size scalpel emits a small jet of helium whose charged particles glow with a vivid lilac hue. An electrode at the scalpel's tip splits some of the helium atoms into a plasma soup of positive ions and electrons.

Unlike in the sun's blazing plasma, the scalpel's ions are relatively slow-moving—so the jet feels like a cool breeze to the touch. But its fast electrons are packed with energy and can convert atmospheric oxygen and nitrogen into reactive forms, including superoxide, nitric oxide and atomic oxygen. These substances can interrupt key metabolic processes and hamper cell reproduction, and researchers have found that cancer cells are much more vulnerable to such effects than healthy cells are. The scalpel can be used on a tumor site for just a few minutes during surgery, says Jerome Canady, a surgeon in Washington, D.C., and part of the team that developed the tool. “We just spray that area with plasma to kill any microscopic tumors,” he says.

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