Directing tubular traffic.

Researchers have shown that they can combine a biological motor and an electric field to steer individual protein tubes along tiny channels of a glass chip.

Within living calls, a two-headed protein called kinesin acts as a biological motor, hauling cargo. Fueled by chemical energy, the protein uses the two heads to "walk" along microtubules, which form an inner scaffold in cells.

Researchers at Delft University of Technology in the Netherlands put a version of this transport mechanism onto the chips. Instead of having kinesin move around, the scientists anchored the molecules so that their heads would propel free microtubules through the channels, explains biophysicist Cees Dekker.

He and his colleagues designed the glass chips with 800-nanometer-deep channels in different traffic patterns, anchored kinesin molecules within the channels, and pumped in a solution of microtubules.

The team started by applying an electric field to a channel on a simply designed chip. When a microtubule entered this channel from a perpendicular path, the negatively charged microtubule turned toward the positive end of the electric field.

In another experiment in more-complex chips, the researchers steered a single microtubule into one of two fork arms.

Then, the researchers put both greenand red-fluorescently labeled microtubules into a channel. As these microtubules approached a fork, the researchers sorted them by color into one or the other arm by switching the polarity of the electric field, they report in the May 12 Science.