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Scientists have used nanotechnology to turn paper into a sensor that can detect toxins in drinking water.

The China–US team dipped normal filter paper into a solution containing carbon nanotubes — which can conduct electricity — and antibodies to microcystin-LR, a common and dangerous toxin.

They dried the paper and repeated the process until enough nanotubes were present to render it conductive.

When the paper is dipped in contaminated water, the toxin binds to the antibodies and affects the conductivity of the nanotubes in the paper by separating them from each other. This change in conductivity is detected by a current-measuring device.

Lead researcher Nicholas Kotov, of the University of Michigan, United States, told SciDev.Net that the test is "fast, sensitive and simple". He said he envisaged that it could be engineered into a matchbook-sized device to test water on the spot.

The sensitivity of the test meets WHO standards for detecting the toxin in drinking water.

"The sensitivity [of the test] is comparable with the best biochemical techniques such as mass-spectrometry and the analysis time is much shorter — at least 28 times — and does not require specialised training," Kotov said.

He said the test could be applied to other toxins and chemicals in water or food simply by changing the antibody.

The method could be used in developed and developing countries. "It is simple to use by anybody," Kotov said.

The main obstacle to manufacturing the test is funding, he said, but he doesn't envisage the test would be expensive as it is paper-based.

Mohamed Abdel-Mottaleb, assistant professor of nano materials at Nile University, Egypt, said the test could enable rapid detection of toxins not only when they enter drinking water systems but also at the point of use.

"This will allow both citizens and governments to monitor and remedy any disturbance in water quality and pre-empt potential health risks due to water contamination."

But he pointed out that carbon nanotubes are neither cheap nor easy to obtain, posing a potential barrier to developing countries. He added that potential health risks from the tubes being released into water supplies should also be studied.

The research was published online in Nano Letters in late 2009.