DNA test detects low-level uranium

Yi Lu and his colleagues, who already showed how synthetic DNA molecules could be used to detect toxic lead at very low levels, have now turned the technique to detecting radioactive uranium in tiny amounts.

Their DNA sensor can detect traces of uranium contamination nearly 3,000 times lower than the level considered hazardous to human health, the UI chemistry professor said recently. The technology eventually might be contained in a fast and easily portable on-site testing system for uranium.

Lu said its likely uses probably don't include sniffing out radioactive weapons, for instance in cargo containers shipped into the country, a potential form of terrorist attack that's raised some concern in recent years. The technique doesn't discern between weaponized "enriched" uranium and the unenriched variety.

But it could be quite useful for detecting contamination levels in soil or water, Lu said.

UI researchers tested it on contaminated soil samples from the U.S. Department of Energy, and it proved to be as capable as the large and complex equipment used in the department's testing labs now.

"The performance is comparable," Lu said. "You cannot take that whole thing (current testing methods) on site for real-time identification."

To create the sensor, the UI researchers use a type of single-strand DNA that "cleaves," or splits, in the presence of uranyl ions, the most soluble form of uranium particles and the one presenting the greatest danger to humans.

To the ribbonlike molecule of DNA, they attach a chemical molecule that fluoresces, or glows, and a second chemical molecule that "quenches" the first one, that is prevents it from glowing.

When a uranyl-containing sample is introduced into the mix, the DNA strand breaks, freeing the fluorescent molecule from the array – and from the effect of the quencher molecule – causing it to glow again.

The UI researchers use the minute light signal to detect the uranium. By capturing how fast the signal begins after a contaminated sample is introduced and how rapidly the signal builds in intensity, they also can tell how much contamination is present.

The researchers identified a type of DNA good for detecting uranium by culling a "library" of trillions of DNA molecules for likely candidates.

"We're basically on a fishing expedition," Lu said. "We do multiple rounds ... with more stringent conditions. We pick out the one that works the best."

They also modify the DNA somewhat, stripping it to the components vital for detecting uranium ions – which also makes it less expensive to produce.

Lu and his team used the same procedure to pick out DNA good for detecting lead and also have identified molecules sensitive to copper and zinc, among other things. The various molecular sensors could be combined in an array, or "DNA chip," able to detect multiple substances at once.

Research on the uranium sensor, outlined in the Proceedings of the National Academy of Sciences, has been funded by the Department of Energy, the National Science Foundation and the National Institutes of Health.

Lu already helped co-found a company, DzymeTech Inc., working to bring lead test kits employing the technology to market, with the idea that homeowners and home inspectors could use them to check for lead in paint or water. The company is licensing the uranium sensing technology as well, he said.

The UI researchers also are looking for DNA molecules that could be used to sense organic toxins like dioxins in addition to toxic metals.

In addition, they're working to understand in more detail the molecular mechanics that make the system work, factors like the structure of the DNA molecules and the way they bind to other molecules – basic science that might help the researchers improve the system further, Lu said.

source news : news-gazette.com