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Nanofibers Power Attoscale Chemistry

A new way to perform experiments using just thousands of molecules.

Researchers have developed a new way to perform chemical reactions involving only about 1,000 molecules. The method could prove useful in the rapid screening of chemical reactions when searching for new drugs and industrial materials.

Crisscross chemistry: This image shows polyurethane nanofibers used to perform attoscale chemical experiments. The nanofibers run perpendicular to one another, and each carries a different reactant, in this case a dye that fluoresces when it reacts with its target. The reaction can only take place at intersections between the fibers when the fibers are heated.

The new system harnesses minuscule chemical reactions that take place at the intersections between polymer nanofibers. The process is cheap and simple; among other applications, it could be used to perform high-throughput testing of new protein- or DNA-identifying labels that improve on those currently employed for sequencing. The process could also be used to detect rare biological molecules such as trace proteins characteristic of the early stages of cancer and other diseases.

Other researchers use microfluidics systems to perform small-scale chemical reactions–networks of minuscule pipes and pumps that direct chemicals around on a chip. The new approach, developed by chemist Pavel Anzenbacher at Bowling Green State University, in Ohio, is completely different. The reactants are suspended in dry polymer nanofibers and only interact with one another where the fibers meet.

Anzenbacher makes the fiber reactors using an established technique called electrospinning. He loads liquid polyurethane into a syringe fitted with a very fine needle, allows a tiny droplet to form on its tip, and then applies a voltage to the tip. Charge repulsion drives the droplet to form elongated polymer fibers, each about 100 to 300 nanometers in diameter. Anzenbacher realized that the technique could be used to create reaction vessels by weaving a grid of the fibers through electrospinning from polyurethane solutions containing small amounts of reactants. Fibers running north-south contain one reactant; fibers running east-west contain another. When the fibers are melded together with a little heat, chemicals at the junctures mix together and react. The products can then be identified using a variety of methods, including fluorescent imaging and mass spectrometry.

In a paper published this week in the journal Nature Chemistry, Anzenbacher describes using the tiny reactors to test four different reactions. The reactions take place between just zeptomoles of molecules–about 1,000 individual molecules.

Two of the reactions used to test the approach involved combining fluorescent-dye molecules, which lit up only when they met their target counterpart on opposing threads. One of Anzenbacher’s areas of research is the development of dyes for detecting a particular protein fragment or DNA base, and he is developing the attoliter (one trillionth of a liter) reaction fibers for high-throughput screening of these dyes. The Ohio system could also be modified for studying thousands of protein interactions using very small samples.

Anzenbacher says that the primary advantage of the fiber reactors over other techniques is the expense. Low reaction volumes are also an advantage when testing new reactions whose products are unknown. “There is no poison poisonous enough that a few molecules would kill you,” says Anzenbacher. What’s more, the reactants and their products are confined within the fibers; they will not vaporize, and they will not spill.

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