Molecular Plumbing

(Originally published by the University of California Los Angeles)

December 7, 2005

The first valve at the nano scale that can trap and release molecules can be controlled, say the researchers, "like a water faucet."

Chemists in the College have created the first nano valve that can be opened and closed at will.

"With the nano valve, we can trap and release molecules on demand," said Jeffrey I. Zink, a UCLA professor of chemistry and biochemistry, a member of the California NanoSystems Institute at UCLA, and a member of the research team. "We are able to control molecules at the nano scale. A nano valve potentially could be used as a drug delivery system."

The valve, said graduate student and lead author Thoi Nguyen, "is like a mechanical system that we can control like a water faucet."

This nano valve consists of moving parts—switchable rotaxane molecules that resemble linear motors designed by California NanoSystems Institute director Fraser Stoddart's team—attached to a tiny piece of glass (porous silica), which measures about 500 nanometers.

(A nanometer is a billionth of a meter; the width of a human hair is about 80,000 nanometers.)

"It's big enough to let molecules in and out, but small enough so that the switchable rotaxane molecules can block the hole," Zink said.

The research was federally funded by the National Science Foundation.

The valve is uniquely designed so one end attaches to the opening of the hole that will be blocked and unblocked, and the other end has the switchable rotaxanes whose movable component blocks the hole in the down position and leaves it open in the up position. The researchers used chemical energy involving a single electron as the power supply to open and shut the valve, and a luminescent molecule that allows them to determine, based on the emitted light, whether a molecule is trapped or has been released.

Stoddart, who holds UCLA's Fred Kavli Chair in nanosystems sciences, has already shown how these switchable rotaxanes can be used in molecular electronics. Stoddart's team is now adapting them for use in the construction of artificial molecular machinery.

The scientists plan to test how large a hole they can block, to see whether they can get larger molecules, like enzymes, inside the container; they are optimistic.

"Building artificial molecular machines and getting them to operate is where airplanes were a century ago," Stoddart said. "We have come a long way in the last decade, but we have a very, very long way to go yet to realize the full potential of artificial molecular machines."

The nano valve is much smaller than living cells, which suggests an intriguing question: Could a living cell ingest a nano valve that carries a drug inside?