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The biosensor produces results 28 times faster than the current method used to detect a chemical compound produced by cyanobacteria, or blue-green algae, known as microcystin-LR.

Commonly found on nutrient-rich waters, microcystin-LR (MC-LR), even in very small quantities, is suspected to cause liver damage and possibly liver cancer. The substance and others like it are among the leading causes of biological water pollution.

It is believed to be a culprit of mass poisonings going back to early human history, says project leader Nicholas Kotov, professor of chemical engineering, biomedical engineering, and materials science and engineering at the University of Michigan.

Water treatment plants—even in developed countries—cannot always remove MC-LR completely, nor can they test for it often enough, Kotov says.

The new biosensor provides a quick, cheap, portable and sensitive test that could allow water treatment plants and individuals to verify the safety of water on a more regular basis.

“The safety of drinking water is a vital issue in many developing countries and in many parts of the United States,” Kotov stresses. “We’ve developed a simple and inexpensive technology to detect multiple toxins.”

The sensor works by measuring the electrical conductivity of the nanotubes in the paper. Before the nanotubes are impregnated in the paper, they are mixed with antibodies for MC-LR.

When the paper strips come in contact with water contaminated with MC-LR, those antibodies squeeze in between the nanotubes to bond with the MC-LR. This spreading apart of the nanotubes changes their electrical conductivity. An external monitor measures the electrical conductivity.

The whole device is about the size of a home pregnancy test, and results appear in fewer than 12 minutes, Kotov says.

To adapt the biosensor for other toxins, Kotov says, scientists could simply replace the antibodies that bond to the toxin. The technology could also easily be adapted to detect a variety of harmful chemicals or toxins in water or food. A paper about the technique was published online in Nano Letters, and will be published in a future print edition.

Chuanlai Xu at Wuxi University in China collaborated on the study, which received funding from the National Science Foundation, the Air Force Office of Scientific Research, and the National Institutes of Health, the  National Science Foundation of China, and the 11th Five Years Key Programs for Science and Technology Development of China.

University of Michigan news: www.umich.edu/news/