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MOLECULAR MEDICINE Streaming through the body by the billions, nanobots could chip plaque from arteries, gang up on bacteria and viruses, scour toxins from the bloodstream, repair broken blood vessels--and dozens of jobs doctors haven't dreamed of yet.
ENVIRONMENTAL CLEANUP Specialized nanobots dumped into an oil spill, a toxic-waste site or even a polluted stream could seek out and find dangerous molecules, remove them or change their chemical structure one by one to render them harmless--or even beneficial.
NIGHTMARE SCENARIO Self-replication is the best way to build a few trillion nanobots in a hurry: each one makes two more, and each of those makes two and so on. But if they don't stop, the entire planet could rapidly be reduced to a teeming mass of robots. Nanotechnologists plan to program their tiny creations to stop reproducing after a certain point. But it takes only one rogue self-replicator to cause a disaster. If you thought computer viruses were a problem...