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Those oscillations successively attract and repel the tip of the tube, making the tube vibrate in sync with the radio wave. As the tube is vibrating, electrons continue to spray out of its tip. When the tip is farther from the second electrode, as when the tube bends to one side, fewer electrons make the jump across the gap. The fluctuating electrical signal that results reproduces the audio information encoded onto the radio wave, and it can be sent to a speaker.
The next step for Zettl and his colleagues is to make their nanoradios send out information in addition to receiving it. But Zettl says that won't be hard, since a transmitter is essentially a receiver run in reverse.
Nano transmitters could open the door to other applications as well. For instance, Zettl suggests that nanoradios attached to tiny chemical sensors could be implanted in the blood vessels of patients with diabetes or other diseases. If the sensors detect an abnormal level of insulin or some other target compound, the transmitter could then relay the information to a detector, or perhaps even to an implanted drug reservoir that could release insulin or another therapeutic on cue. In fact, Zettl says that since his paper on the nanotube radio came out in the journal Nano Letters, he's received several calls from researchers working on radio-based drug delivery vehicles. "It's not just fantasy," he says. "It's active research going on right now."
A nanoradio is a carbon nanotube anchored to an electrode, with a second electrode just beyond its free end. When a voltage is applied between the electrodes, electrons flow from a battery through the nanotube, jumping off its tip to the positive electrode. A radio wave alternately attracts and repels the nanotube tip, causing it to vibrate in sync. When the tip is farther from the electrode, fewer electrons bridge the gap; the varying electrical signal recovers the audio signal encoded by the radio wave.
Credit: John Hersey