New device lab-on-a-chip sensor to detect milk contamination

Whitaker investigator David Beebe, Ph.D., of the University of Wisconsin-Madison has developed a process to make on-demand, miniature sensors for a wide variety of poisons, including naturally occurring contaminants and intentionally introduced toxins.

The sensors can be constructed to test for a particular toxin in as little as an hour with test results available in minutes.

The Wisconsin group, with Homeland Security funding, is focusing on the nation's milk supply, which comes from a widely dispersed system in which large amounts of the highly perishable product are quickly collected and distributed.

With a short cow-to-consumer timeline, contamination could affect large numbers of people before being detected. It might be possible, however, to incorporate sensors in food packaging that could tell if the package is disturbed or the contents are contaminated.

Beebe's group reported in a paper to be published in the journal Electrophoresis that disposable sensors can be manufactured on-demand in an inexpensive process. With collaborator Eric Johnson, Beebe tested the technique to rapidly detect the botulism toxin, botulinum neurotoxin, the most poisonous substance known.

"Although outbreaks due to contaminated food are rare, the infection can have a profound impact on areas in which the outbreaks occur," Beebe and his colleagues reported. "Due to its high specific toxicity, botulinum toxin is also considered a potential agent for use in bioterrorism."

The botulinum toxin can be detected in blood or food using a standard test that takes up to four days to produce results. But the only treatment is an antitoxin that must be given right away. A lab-on-a-chip could produce faster results for more rapid treatment.

Beebe's design and fabrication process, which he calls microfluidic tectonics, uses light to freeze a liquid into the solid shape of a component, such as a valve, in the precise physical location where the component is needed.

Biological tests can require different steps performed in different sequences. Each test requires a particular arrangement of components, such as check-valves, channels, mixers, pumps, and filters. Beebe's modular approach allows the flexibility to design and fabricate a wide range of test chips from a single toolbox of components.

"Multiple functions such as diluting and mixing blood, separating whole blood to serum and cells, and detecting botulinum toxin in the serum are performed in the device," the researchers reported.

The device needs no power supply and uses no electronic parts. A blood sample is placed in a chamber on the chip and then the test set into motion by squeezing the chamber. Positive results appear as a color change visible to the naked eye.

The current research was supported by the Defense Advanced Research Projects Agency. The Department of Homeland Security has made a $15 million grant to a national consortium of academic, private and government organizations investigating ways of detecting and preventing food contamination. Beebe's work will be supported through the University of Wisconsin-Madison, a member of the consortium.

In 1996, Beebe received a Whitaker Foundation Biomedical Engineering Research Grant for a project in tactile sensors. In addition to biosensing, his current research focuses on the use of microfluidics to understand cell behavior.

Contact: David Beebe, University of Wisconsin-Madison Frank Blanchard, The Whitaker Foundation