For just a few dollars, the tiny chips- which sense potential toxins in molecule-sized samples-can now be fabricated in hours, not weeks, and at room temperature instead of in vacuum ovens.

The method developed at Purdue (West Lafayette, Ind.) mates specially selected and prepared nanoscale "wicks" with easy-to-assemble polymer deposition. The chips and the postage-stamp-sized analytic devices made with them have potential applications in food safety, biosecurity, clinical diagnostics, pharmaceuticals and electronics, according to the researchers.

Microfluidic chips employ nanoscale channels through which samples of potential toxins are sensed in molecular-sized quantities, enabling these "chemistry labs on a chip" to give early warning of danger before it accumulates to dangerous levels.

Until now, expensive high-temperature semiconductor ovens were required to fabricate the microfluidic channels through which the chip-mounted chem lab senses the world. But the Purdue method uses off-the-shelf polymers and nanoscale fibers to create microfluidic chips inexpensively, at room temperature, in about two hours.

"We have brought the design and manufacture of these microfluidic devices within the reach of any engineer or scientist, who can now easily test their ideas and conduct research within a typical laboratory setting," said Michael Ladisch, a biomedical engineer who developed the technique with assistance from Tom Huang, a graduate student in chemical engineering. "This whole device can be developed and in operation in less than two hours."

Microfluidic devices use nanoscale techniques to sense as little as a single molecule of a known toxin. Usually a silicon substrate is used. Channels are grown on it through photolithography and high-temperature vapor deposition. But Ladisch uses a glass substrate, placing fiber wicks on it, then fixing them in place with a flexible polymer, polydimethylsiloxane (commonly known as PDMS).

Using glass microscope slides and tweezers, thin glass fibers are placed atop the glass, after which the PDMS is press-fit over the assembly. The sandwiched fibers act as wicks, sensing the world at one end and delivering molecule-sized samples of what they sense to the other end of the channel.

The tests, done with fiber wicks in the micron-sized range, demonstrated how different types of proteins could be separated from a mixed solution. But the microfluidic device itself could have much broader applications. For instance, not only do different types of fibers enable selective sampling of the environment, but chemistry inside the channel can determine what flows through and what sticks, so that different types of molecules could be separated out, streamlining the sensing of airborne toxins, foodborne pathogens and biological agents and diagnosing disease.

Also contributing to the project were Nate Mosier, an assistant professor of agricultural and biological engineering; Rashid Bashir, an associate professor of electrical and computer engineering; researchers Woo-Jin Chang and Demir Akin in electrical and computer engineering; and Rafel Gomez, a graduate student in electrical and chemical engineering.