Cut-ups create soft spots for chemistry

It’s the kind of chemistry laboratory you might expect in a Gary Larson cartoon. Instead of glassware connected by convoluted tubing, this submerged lab sports squishy vesicles as small as cells, and they’re linked via elastic tubules only a few molecules in diameter. All that’s missing is a goofy amoeba-scientist in a white coat.

Fluorescent stain makes this four-liposome network glow. Micrographs: Karlsson et al./Nature

Particle (arrow) moves through tubule connecting vesicles.

In fact, this type of microscopic laboratory is well beyond the comics-page stage. In the Jan. 11 Nature, Swedish researchers report creating prototypes with sets of up to 11 minuscule soft vesicles.

Such networks may someday serve as sensors, chemical reactors for processing a single molecule at a time, or even chemical computers, says Owe Orwar of the Chalmers University of Technology in Göteborg. The networks may also provide an even tinier alternative to current lab-on-a-chip devices made with methods borrowed from the microchip industry (SN: 8/15/98, p. 104). “If we want to shrink the chip-based systems even smaller, we have to think in new ways,” such as this vesicle-based approach, Orwar says.

“This is nanoengineering of molecular assemblies at its best,” says Richard N. Zare of Stanford University.

To create the networks, Orwar and his coworkers from Göteborg University make layers of soaplike molecules, called phospholipids. These assemble into cell-like vesicles, or liposomes. Then, by pushing down on the vesicle with a carbon fiber, the researchers force a waist to develop.

From this configuration, they can create minitubing. The plastic surface beneath the vesicle is sticky, so when the scientists tug on one end of the pinched-vessel configuration, the other end stays put. The waist then stretches into a tube. By repeatedly subdividing the mother liposome or newly formed daughters, the researchers add to the network.

The act of drawing long tubes out of liposomes is not new. Canadian and American scientists first reported doing it in 1996 to make templates for the wires needed in nanoscale electronic circuitry.

Focusing on the vesicles as much as the tethers that link them, the Swedish scientists have now shown that the networks are capable of both independent and coordinated operations vital to a microlaboratory. Besides carrying out different chemical reactions in different vesicles, the researchers were able to transport particles through a tubule from one vesicle to another.

What’s “particularly interesting” about the new work “is the ability to control the composition of separated liposomes,” comments Jeffrey G. Linhardt of the University of Massachusetts in Amherst. If vesicles can be charged with substances that can be independently switched between two chemical states, it even might be possible to build tiny chemical computers, Owar speculates.

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