Tiny gold particles 13 billionths of a meter in diameter and synthetic DNA that reacts to toxic lead have been combined by University of Illinois researchers to create a lead-detecting sensor.
The method can detect lead, in paint for example, at a level of as little as 20 parts per billion, far below the safety limits the U.S. Environmental Protection Agency uses.
The research could provide an inexpensive, accurate test that anyone can use to check for lead, said UI chemistry Professor Yi Lu. The university has applied for patents on the techniques involved, and Lu and colleagues are examining commercial possibilities.
"This is quite close," Lu said recently. "It's less than five years, maybe two to three years."
He said the challenge now is to package the system in a way that makes it foolproof. The UI researchers take samples and mix them in a solution with the gold nanoparticles and the DNA, fine for chemists but not something the average consumer wants to do.
Lu envisions a small pre-packaged container of solution to start, into which a sample can be dropped.
Eventually, the researchers want to develop a swab or strip that can be placed in contact with a surface and will signal the presence of lead by changing colors, something like litmus paper.
Lead detection now mostly involves time-consuming lab testing of samples, or expensive portable equipment that requires a trained operator, or inexpensive sensors that aren't very accurate.
The UI techniques could provide a test that's accurate even when applied by a non-expert, easily portable, fast and cheap.
"The material itself costs in cents, not dollars," Lu said.
The system works because the synthetic DNA causes the gold nanoparticles to aggregate in clusters that give off a blue color.
In the presence of lead, the DNA reacts, in essence breaks apart, and the aggregation fails to occur, creating a color shift to red.
In addition, the more lead that's present in a sample, the more red the color becomes, revealing the degree of lead contamination as well.
More than two years ago, Lu and his graduate students began culling a huge database of DNA trying to find types that reacted to lead and to pin down the best candidate.
"We start with a large DNA library, a DNA library of 100 trillion molecules," Lu said.
They use the DNA in conjunction with gold nanoparticles because scientists have studied those particles extensively, so their properties are well characterized, and because the DNA attaches easily to them.
The package also has the "colorimetric" properties the researchers are looking for, the shift in colors and color intensity in the presence of lead.
Lu and graduate student Juewen Liu outline the technique in an article to be published in the Journal of the American Chemical Society, which already has appeared online.
The U.S. Department of Energy and the National Science Foundation have funded the work.
While lead in old paint and elsewhere in the environment is a major concern - too much in the body can lead to brain damage, particularly in children, as well as other organ damage, headaches and bone pain - the UI-developed sensing method may not be limited to detecting that substance alone.
The researchers are looking for other types of DNA that react, for instance, to mercury and arsenic, also toxic substances for which there aren't any practical sensors at present.
Lu said the different kinds of DNA could be combined in an array, or "DNA chip," to detect various substances at the same time.
"You can actually have a battery of all the different tests," Lu said. "That's, I think, really the potential of this technology."
You can reach Greg Kline at (217) 351-5215 or via e-mail at firstname.lastname@example.org.