First Light-Driven Nanomachine

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Described in the journal Nature, the Yale circuit "represents a technical breakthrough," says Columbia University mechanical-engineering professor James Hone. "It opens up a new way to make opto-mechanical switches that can reroute one optical signal using another." Hone says that such devices could be the building blocks of optical circuits. Adam Cohen, a professor of chemistry, chemical biology, and physics at Harvard, agrees--as long as making these devices proves compatible with standard semiconductor processing. The traditional approach, which involves converting the optical signal into an electrical one and back again, "slows things down and is more complicated," Cohen says.

Because the mechanical oscillation of the beam changes the way that light flows through it in a measurable way, the beams could be developed into very sensitive chemical sensors, says Hone. The Yale group has not demonstrated a chemical sensor. In theory, however, arrays of the on-chip silicon oscillators could be decorated with antibodies that bind blood proteins characteristic of diseases such as cancer. If a blood sample placed on the chip contained a small amount of the protein, it would bind to the silicon beam, changing the frequency of its oscillations--and thereby causing a measurable change in the speed of light carried through it. Other nanoscale sensors work on a similar principle, picking up differences in the flow of electrical current through oscillating silicon beams or carbon nanotubes when they bind to molecules of interest. Optical resonators might be even more sensitive, says Hone, because optical devices are "better behaved," giving clearer signals than electrical devices do.

However, such applications are many years away. The device is still in very early development in Tang's lab, where his group is refining its mechanical properties.